-2147483648	Sources for this outline

				-2147483648	Field work

				-2147483648	Comparative work

				-2147483648	Are “races” biologically distinctive?

				-2147483648	Human genes and other primates

				-2147483648	Human genes suggest migration patterns

				-2147483648	How do populations adapt to disease?

				-2147483648	How do populations adapt to attitude?

				-2147483648	Notes from Anthropology

				-2147483648	Jane Goodall and the Chimpanzees of Gombe

				-2147483648	Types of primates

				-2147483648	Types of primate societies

				-2147483648	Primate extinction

				-2147483648	Overview of Primates and Primatology

				-2147483648	Prosimian Primates

				-2147483648	New World monkies

				-2147483648	Owl monkey. Like slow loris has large eyes. The eyes of the owl monkey and slow loris are examples of convergent evolution. We know that the owl monkey’s ancestor had small eyes. Large eyes were independent adaptations to night-living in both owl monkeys and slow lorises.

				-2147483648	Uakari. (The “bald” brightly orange-headed monkey.) Why does the uakari have such brightly colored fur on its head? Hamilton suggest the evolutionary advantage of sexual species is to mix genes, a good defense against parasites. He suggests that uakari males, when brightly colored, indicate that they are healthy and fit mates for females— that they are parasite-free. More on this later.

				-2147483648	Cottontop tamarin. Some tamarins are polyandrous, a female has several male consorts. These males help rear offspring. One explanation for this mating system is that tamarins frequently have twins. Raising twins require much parental attention, hence, the advantage of multiple mates.

				-2147483648	Old World monkies

				-2147483648	Japanese macaques. (The “hot tub” monkeys.) Form complex social groups.

				-2147483648	Black and white colobus monkey. Large leaf-eating monkey.

				-2147483648	Vervet monkeys. Interesting communication system. They emit different calls for different kinds of predators (leopards, hawk, humans, snakes). Are these calls instinctual or learned?

				-2147483648	Gelada. (Monkey with bright-red chest mark). Have unusually large social groups. Why? Why do geladas form large groups while other primates are usually solitary? Understanding factors controlling group size provides insight in the development of social groups during human evolution.

				-2147483648	Close up of baboon mouth and teeth. Baboons are highly sexual dimorphic. The sexes differ in body size and proportions. For example, males have large canines, females have small canines. Why are males and females almost identical (such as tamarins) in some species but very different in others? Is there a connection between a species’ mating system and sexual dimorphism?

				-2147483648	Close up of baboon estrus swelling. In some species, such as baboons, females show highly visible swellings in their rears when they are ovulating. Males tend to be more interested in females during periods of estrus swelling than at other times. One could theorize that males attending to estrus swellings are more likely to impregnate females and produce more offspring than males uninterested in females during these times. Hence, male attraction to females in estrus may be advantageous, favored by natural selection.

				-2147483648	Meat-eating baboons. Some primates hunt and consume other animals. Meat is viewed as a critical resource. At one time paleoanthropologists viewed hunting as a critical force in human evolution. This is often called the “Man the Hunter” Model. Currently, most paleoanthropologists reject this view as being male-biased (ignoring the contribution of females in human evolution) and there is little evidence that hunting was a major force in early human evolution.

				-2147483648	Apes

				-2147483648	Siamang. Mode of locomotion is brachiation, swinging through the trees. Siamangs and a related species, gibbons, live in small territorial groups and engage in singing duets.

				-2147483648	Orangutan. Southeast Asia. Mode of locomotion is quadromanual climbing, require all four limbs to move through the canopy. Like siamangs and gibbons, they are arboreal, spending most of their time in trees.

				-2147483648	Gorillas. Intelligent, complex social behavior. Genetic and molecular research indicates that humans are closely related to gorillas and chimps; it was previously thought gorillas and chimps were more closely related to orangs than to humans.

				-2147483648	Chimps. Similar to us in many ways. Use a suite of tools. Males stay together while females migrate out. On the border zones of their home ranges, groups of males attack and try to kill solitary chimps not belonging to their group. Similar to human warfare.

				-2147483648	Overview of Cultural Diversity and Cultural Anthropology

				-2147483648	About 20000 to 10000 BP, cave painting, bone tools, statuettes such as Venus figurines, and shelters were made. Population increased and societies became more complex.

				-2147483648	In the last 10000 years, ways of subsisting diversified; agriculture and pastoralism appeared. In the last 6000 years, state societies (civilizations) emerged such as the Inca of Peru along with money (e.g., the stone money of Yap and other Pacific islands). Marriage practices and other customs (such as hair styling) diversified.

				-2147483648	The diversity of social systems and customs require cultural anthropologists to be tolerant rather than judgmental. Cultural anthropologists try not to rank some customs or beliefs as inherently superior or better than others.

				-2147483648	In addition to examining customs and social systems, some cultural anthropologists consider child-rearing practices and personality. A traditional area of research has been the relation between culture and personality.

				-2147483648	Evolutionary Theory

				-2147483648	History

				-2147483648	Evolutionary theory is a very comprehensive theory explaining differences among species, why species change through time, and why organisms fit so well in their environments.  During the Enlightenment, the Biblical account of life was weaken by the observation that fossils appear to fit into family trees; that fossil species change over time. In addition, geologists, such as Lyell, argued that the Earth is millions, rather than thousands, of years old.

				-2147483648	Lamarck accounted for change in fossil and living species. He proposed that individuals acquire traits during their lifetimes and that these traits are passed on to their offspring. Traits are acquired and inherited. Giraffes stretch their necks to reach leaves and pass on the trait of long necks to their offspring (this example is only approximation of Lamarck’s hypothesis). Lamarck’s hypothesis can be tested by chopping tails of a hundred rats. Lamarck would predict that offspring of these tailless rats should be tailless (or at least have shorter tails). They don’t, thus the prediction is falsified.

				-2147483648	Darwin

				-2147483648	Darwin accounted for change in fossil species by natural selection—his most significant idea. He observed three facts:

				-2147483648	(1) All species have high potential fertility

				-2147483648	(2) But populations observed in nature tend to be stable

				-2147483648	(3) Natural resources, especially food, are limited

				-2147483648	He deduced that as more individuals are produced than can be supported by the environment, there is competition among individuals to survive. Darwin was impressed by two other facts:

				-2147483648	(1) Individuals, even in the same species, are not identical

				-2147483648	(2) Variation among individuals is inherited (e.g., one can breed for certain hair color and personality traits in dogs.)

				-2147483648	From these facts, Darwin made several inferences. First, survival is not random but depends on inherited traits. Secondly, this differential survival leads to change in species over generations (evolution) and the emergence of new species (speciation). Natural selection is the main mechanism for this change. Advantageous traits (e.g., longer legs, sharper teeth, attractive feathers) are inherited and individuals with these traits tend to produce more descendants than individuals lacking these traits. These traits are said to be selected. Over long periods of time, natural selection can cause speciation. If two populations of a species become isolated (perhaps by a new river), and if their environments become different, the two populations are likely to become two separate species—unable to interbreed.

				-2147483648	What are the important forces in evolutionary change? Darwin hypothesized five hostile forces:

				-2147483648	(1) Food shortages

				-2147483648	(2) Predators

				-2147483648	(3) Parasites (disease)

				-2147483648	(4) Climate (e.g., frequent hurricanes)

				-2147483648	(5) Competition for mates. Mate competition involves sexual selection (not to be confused with natural selection). Discussed later.

				-2147483648	Natural selection (or selection) produces adaptations. Although it has different meanings, an adaptation is an advantageous trait produced by selection. A tiger’s canine is an adaptation. Better canines increases the likelihood of better hunting, better survival, and more descendants.

				-2147483648	Evolution, replicators and vehicles

				-2147483648	The key distinguishing feature of life and the necessary ingredient for evolution is replication, the ability of an individual to make copies of itself. Replication is not perfect, mutations occur in genetic material, DNA. But without replication, no heritability, hence, no evolution.

				-2147483648	An important issue in evolutionary theory is what level we consider adaptations and replications. Can groups be said to be adaptive or only individuals? One evolutionary theorist, Richard Dawkins, argued in his book the Selfish Gene, that we should talk about adaptation and replication at the level of the gene. In his view of life there are replicators—things that make exact copies of themselves—and vehicles—a robot produced by a replicator in order to make more replicators. Chickens, cats, and oak trees are vehicles. Replicators (genes) live in these vehicles. Some vehicles are more advantageous than others and allow more replicators to be perpetuated. Dawkins believes that the gene is the basic replicator in life. To anthropomorphize, a chicken is a gene’s way of producing more copies of itself. We will discuss the issue of levels of adaptation and replication later.

				-2147483648	Causes

				-2147483648	In explaining a trait, evolutionary researchers use four levels of explanation. They are:

				-2147483648	Proximate Cause The underlying mechanism of the trait. The physiology. Example: Why does a bird sing? Testosterone and lengthening daylight stimulating the song-producing centers of the brain.

				-2147483648	Ultimate Function How did natural selection favor this trait? Example: a bird sings to attract mates. Singing individuals are more likely to attract mates than individuals that do not sing.

				-2147483648	Ontogeny The development of the trait through the individual’s lifetime. Example: Do birds learn to sing? Will they sing if raised apart from others? Do immature birds sing?

				-2147483648	Phylogeny What is the evolutionary history of the trait? Example: Do robins and sparrows sing because of their common ancestor was able to sing? Or is singing in robins and sparrow independent adaptations?

				-2147483648	Common error in thinking about traits

				-2147483648	The textbook makes a typical mistake in discussing whether a trait is “biological” or learned. The author assumes that if a trait is universal throughout a species it is “biological” and, hence, genetic. For example, if all human societies have incest rules than incest-rule making must be a genetic trait. Conversely, if a trait is flexible (changes over time) then it is learned and not “biological.” These assumptions are fallacious. Consider the Arctic hare. During winter, its fur is white, during summer it is brown. The fur changes color during the seasons and offers good camouflage (an adaptation). If the above assumption is correct than the hare’s fur change must be a learned trait because it is flexible. It is not. Most traits, especially behavioral ones, depend on both the animal’s genetic constitution and environment. Learning has a biological basis and the distinction between “learned” and “biological” is rarely clearcut, both are deeply interconnected. This is an important point—be sure you understand it.

				-2147483648	Primate species are divided into four taxonomic groups: Prosimians, New World monkeys, Old World monkeys, and Apes (including humans). Species are classified by important physical traits. Some traits among species are homologous—species have these traits because they all shared a common ancestor that had these traits. Example: humans and dolphins both breath and their common ancestor could breath. Breathing in humans and dolphins is a homologous trait. Other traits among species are analogous. Bats, birds, and bugs have wings NOT because of a shared ancestor but because wings are independent adaptations. Dolphins and fish have fins because fins are adaptations to moving through water. The ancestors of dolphins walked on land (in fact, dolphins and other whales sometimes have vestigial non-functioning hip bones). As they adapted to marine environments, ancestral dolphins evolved fins similar to fish. Wings and fins developed independently in many species; they are analogous traits.

				-2147483648	Darwin’s Challenge. The theory of evolution by natural selection can be falsified if you can show that any organ in any species has evolved to help another species.

				-2147483648	Recap: Evolution occurs when some genes become rare in a population and others common. Underlying evolution is heritability. Darwin recognized this but did not know the exact mechanism. We now know that a gene is considered a replicator—it makes an exact copy of itself.

				-2147483648	Natural selection changes the distribution of genes. Natural selection does not necessarily promote more complex features over others. A common misconception about evolution is that it is a process where simpler species become more complex, inferior organisms become superior. It is not. EVOLUTION IS NOT THE SAME AS PROGRESS! Natural selection is a mechanistic process, it doesn’t make value judgments about which traits are “better” than others.

				-2147483648	Ecological Concepts

				-2147483648	Ecological Niche: An ecological opportunity or “life style” that a species occupies. For example, the tarsier’s ecological niche is eating insects in trees. Tarsier’s features are selected to help get tree-living insects at night.

				-2147483648	Competitive Exclusion: Species specialize—they occupy different niches. No two species can occupy an identical niche at one time. One species outcompetes another species. Excellent analogy: consider downtown yogurt shops. If two yogurt shops were established side-by-side you would not expect both to last very long. In a short while, one shop remains, while the other goes bankrupt, moves away, or finds a different marketing niche.

				-2147483648	Adaptive Radiation. When species move into a new area, where niches are unoccupied, population quickly become specialized—establish themselves in different niches. Case example: Madagascar lemurs moved into the island of Madagascar millions of years ago. They had few competitors. Lemur populations quickly speciated—developed into new species—each occupying a different niche. See figure.

				-2147483648

				-2147483648	Taxonomic Concepts

				-2147483648	Homologous trait: when two species share a trait because of a common ancestor. Example: two arboreal species are arboreal because their common ancestor was arboreal.

				-2147483648	Analogous trait: two species share a trait NOT because of a common ancestor but because both traits were independently developed (convergent evolution). Think of echo-location in bats and dolphins or fins in dolphins and fish.

				-2147483648	We want to group species by homologous traits not analogous traits because we want our taxonomic trees to reflect evolutionary relations.

				-2147483648	Adaptation

				-2147483648	Do adaptations benefit the species, the social group, or the individual? Darwin was not sure. This is a major issue in evolutionary biology.

				-2147483648	The Old View. During the 50s and 60s, evolutionary biologists believed that adaptations were for the benefit of the group. Example: groups of lemmings jump off cliffs and drown in Norwegian fjords. Biologists considered this “mass suicide” as a population-control adaptation benefiting the species. They assumed that if lemmings did not kill themselves in massive numbers their species would be jeopardize by extinction  through overpopulation. Similarly, biologists believed that organisms age and die to make way for a new generation of healthy vigorous individuals.

				-2147483648	But wait! Lemming so-called suicide can be looked at from lower levels. If a gene (or a group of genes) dispose lemmings to kill themselves, what happens to that gene? It exterminates itself when a lemming drowns. How can such genes be passed on? How can natural selection favor individuals to kill themselves.

				-2147483648	We now have a simpler explanation for lemming “suicide.” Lemmings don’t deliberately kill themselves, they jump in fjords to swim to the other side. They do so during times when their native ranges are overpopulated and food is unavailable. While swimming to the other side many die, but many make it to a new area where food is available.

				-2147483648	Many theories and hypotheses turn out wrong and in this class we will review the failures as well as the successes.

				-2147483648	Selection for Altruism

				-2147483648	Currently, most (but not all) biologists and anthropologists believe that natural selection operates most powerfully at the level of the individual rather than the species or group level. Adaptations are generally viewed as benefiting the individual. Selection is not expected to favor pure self-sacrificing behavior in species (pure altruism). It can, however, favor cooperation and seemingly unselfish behavior. How?

				-2147483648	Kin selection. Darwin noted that some social insects such as bees and ants have sterile castes of workers. Rather than reproduce, these workers help others. Why? How can selection favor individuals to act “unselfishly” towards others? Natural selection can favor helping behavior among individuals that are highly related to each other. Relatives are likely to share the same genes. From a gene’s view, helping someone who has a copy of your gene (such as a brother or sister), helps perpuate more copies of yourself. Among certain species of bees and ants, workers help relatives to reproduce and, in doing so, help perpetuate their genes. This kind of nepotism is called kin selection (not to be confused with natural or sexual selection). Individuals act selectively to help relatives more than non-relatives.

				-2147483648	Reciprocity. A second way natural selection can favor seemingly unselfish behavior is by reciprocity—I’ll scratch you’re back if you scratch mine. An individual may help another, even a non-relative, at one time and expect the recipient of help to return the favor in the near future.

				-2147483648	Reciprocity and helping kin are the fundamental building blocks of primate societies, including human societies.

				-2147483648	Here are two further examples of adaptations viewed from the level of the individual and the group.

				-2147483648	First Example: Why live in groups?

				-2147483648	In some primate species, such as tarsiers, individuals live alone. In other species, such as gelada baboons, individuals live in large groups. What are advantages of living in groups?

				-2147483648	The Old View: Primatologists once thought baboon troop structure benefits the group. They noted that females and dominant male baboons tend to be in the core area of the group while subordinate males tend to be on the periphery of the troop. Early primatologists viewed subordinate males as being altruists—they put themselves at risk, exposing themselves to predators, for the good of the group. Being weak and less aggressive, subordinates are presumably more expandable than dominant males and females.  Primatologists assumed that this group structure as an adaptation. Without it, the group would become extinct.

				-2147483648	The New View: But wait! If you were a subordinate male, would you hang around the fringe of the troop, exposing yourself to tigers, and sacrificing yourself for your group? Would a gene promoting such behavior last long? Probably not. The new view of baboon and other primate social groups is to consider advantages of group living for the individual. These are:

				-2147483648	Predation protection. Living in groups reduces the chance you will get eaten by a predator because of cooperative defense. A group is more likely to ward off attacks than a solitary individual. Also, in large groups, such as schools of fish, flocks of birds, and herds of ungulates, living in groups reduces the chance that YOU will be eaten. Maybe your neighbor might get eaten but few predators are likely to consume all fish in a school or antelopes in a herd. This last explanation is referred to as the selfish herd. Living outside a herd or school, by yourself, increases the chance a predator will eat you if he spots you.

				-2147483648	Food gathering and defense. Wolves can successfully bring down a moose because they hunt in cooperating groups. Primates, such as chimps, gather in groups to defend valuable food areas such as fruit trees (this particular example is an important issue in understanding primate society).

				-2147483648	Localized resources. Individuals may gather in groups not because they like each other but simply because valuable resources are clumped in a small patches. Example: a certain baboon species likes to sleep on cliff ledges (a good way to avoid lions). They gather at these cliff sites at night and, by consequence, sleep in groups.

				-2147483648	Altruism

				-2147483648	How can natural selection favor self-sacrificing, cooperative, altruistic behavior? Pretend you are a gene. As a gene, you should be interested in promoting copies of yourself (recall the concept of a replicator). In individuals, relatives, such as siblings, are likely to share the same copies of genes. If you are a gene in an individual, the individual’s brother is likely to have a copy of you. If the individual helps his brother to survive and reproduce, copies of yourself will be promoted. Inclusive fitness refers to this notion. Relatives share copies of genes. By helping each other, relatives increase the frequency of copies of their genes.

				-2147483648	Example: Alarm-calling among vervet monkeys. Recall that vervets have different alarm calls to warn others of predators. Calling out when a predator is approaching is a risky behavior. The caller draws the attention of the predator to herself. Why doesn’t selection act against this “altruistic” trait? A kin selection/inclusive fitness explanation is that vervets call out to warn relatives, not the entire group. Older females call out more than older males. In vervets (and other primate societies) males emigrate to new groups, females remain in the group they were born in. Older female vervets are more likely to have relatives than older male vervets. Hence, their likelihood in calling out makes sense according to the kin selection hypothesis.

				-2147483648	Reciprocity

				-2147483648	Another way natural selection promotes cooperation is by reciprocity—an exchange of favors. (Example: two baboons grooming each other, one after the other.) Reciprocity becomes complex because of the possibility that individuals cheat or deceive.

				-2147483648	Why sexual dimorphism in species?

				-2147483648	Recall that males are larger than females in some primate species and females larger than males in others. In some species, there is little sexual dimorphism. Why?

				-2147483648	Hypothesis 1: Niche divergence. Perhaps males and females are of different size because they inhabit different ecological niches, having different diets and different ways of getting food (foraging strategies). Example: Orang females might be lighter than males so they can forage in the higher part of the forest canopy.

				-2147483648	Hypothesis 2: Intrasexual competition. Perhaps males are larger than females in some species because males compete with each other by aggression. Females might be larger than males in other species because of intense female aggression. Generally, size is an important asset in violent competition, especially in ground-living species.

				-2147483648	Hypothesis 3. Body size. There may be size differences between sexes related to the body size of the species. Larger species, generally, are more likely to have larger variation in body size because they take longer to grow to mature size.

				-2147483648	Hypothesis 4: Predation. One sex might be larger than the other to protect the group from predators.

				-2147483648	Which hypothesis is the best explanation for sexual dimorphism? Using the comparative approach (an approach that Darwin pioneered) we can see which hypothesis has the strongest support. In the comparative approach, we collect information on, say, a hundred primate species. We note each species mating system, body size, niche specialization, vulnerability of predation, and extent of their sexual dimorphism. Then we examine associations among these variables much like Goldman did in his susto study. Niche divergence hypothesis receives a little support but generally species with a strong degree of sexual niche divergence or not likely to be highly sexual dimorphic. Likewise for the body size and predation hypotheses. (The body size hypothesis is difficult to test, however, because terrestrial primate species tend to be larger than arboreal species.)

				-2147483648	The strongest association is found between mating systems and sexual dimorphism. Male-male competition is generally more intense in polygynous species (where a male has several mates). Polygynous species tend to be the most sexually dimorphic. Monogamous species (one a male has one mate) tend to be less sexually dimorphic. Importantly, in polyandrous species (where a female has several mates), where female-female competition is high, females tend to be bigger than males. The intrasexual competition hypothesis is the most difficult of the four hypothesis to falsify.

				-2147483648	Sexual Dimorphism

				-2147483648	The best explanation for sexual dimorphism involves competition. In polygynous systems, where males competes for mates, males tend to be larger and have larger canines than females. In monogamous and polyandrous societies, where mate competition is less intense, males and female tend to be the same size.

				-2147483648	Review

				-2147483648	Group v. Individual Levels of Adaptation

				-2147483648	Kin selection/inclusive fitness and reciprocity

				-2147483648	Group formation

				-2147483648	Sexual dimorphism

				-2147483648	Example of Evolution by Natural Selection

				-2147483648	Moths: In the same species of an English moth, there are two variants: dark and white. As pollution increased during the 19th century, English trees became soot covered. On such a dark background, white moths stand out and are more likely to be eaten by birds. Dark moths, however, are camouflaged. Dark moths increased in the population. As coal pollution decreased during the 20th century, English trees became less soot covered, hence, lighter. On a light background, dark moths are conspicuous to predators. Their numbers decreased while the white variant of moths increased. This case illustrates evolution by natural selection over a short period.

				-2147483648	Group v. Individual Levels

				-2147483648	Most evolutionists currently believe that natural selection works almost exclusively on individuals, not groups. Recall that selection involves differential survival and reproduction. Individuals die out and reproduce much faster than groups. Hence, it is thought that selection is stronger on the level of individual rather than groups.

				-2147483648	Consider several groups of individuals. All groups are composed exclusively of individuals that have a gene causing them to sacrifice themselves when population density is high. (Recall the old view about lemmings.) This traits is advantageous for the group as they can limit their numbers when resources are limited. Hence, they are less likely to go extinct. Groups of such individuals are better able to survive and colonize new areas.

				-2147483648	BUT this model is highly unlikely. Consider a mutation that causes one individual NOT to sacrifice herself. What happens? In a population of altruists (self-sacrificers) this “selfish” gene will spread and quickly predominate in the population. Altruists kill themselves while individuals with selfish genes survive and prosper.

				-2147483648	NOTE! When we speak of a gene for altruism or a gene for selfishness we are speaking in shorthand. In reality, few traits are caused by a single gene. And recall that behavioral traits are a product of both genotype and environment. The above example is hypothetical illustrating why selection of groups are unlikely. It is unlikely that there are single genes for altruism and selfishness.

				-2147483648	Principal point: selection is stronger on individual than groups because individuals reproduce and die faster than groups.

				-2147483648	Group Formation

				-2147483648	Disadvantages for the individual: increased competition for food and mates, parasites, disease.

				-2147483648	Advantages for the individual: protection from predators, cooperative food-getting, localized resources.

				-2147483648	Example: tarsiers are nocturnal (forage at night) and are insectivores (eat insects). As such a niche requires stealth, tarsiers are solitary. Terrestrial diurnal (foraging during daylight) folivores (grass-eating) primates, such as geladas and baboons, live in large groups. (Terms: Insectivores: insect-eating; folivore: grass/leaf eating; frugivore: fruit eating.)

				-2147483648	Estrus Swellings

				-2147483648	Some primates have estrus swellings usually occurring for a few days every month There is considerable variation among species, however. In bonobos, a kind of chimpanzee, swellings last for a few weeks. Estrus swellings peak during ovulation.

				-2147483648	Why?

				-2147483648	Prosimians/Tarsiers Lemurs Tarsiers

				-2147483648	Old World Monkey Baboons Guenon

				-2147483648	New World Monkey Squirrel monkeys Marmosets

				-2147483648	Apes Bonobos Gibbons

				-2147483648	Mating System Polygyny Monogamy/Polyandry

				-2147483648	Male Competition High Low

				-2147483648	MALE Parental Care Low High

				-2147483648	Estrus swelling occurs more frequently in polygynous species where males provide little parental care. Monogamous and polyandrous species, where males provide parental care, are less likely to have estrus swelling.

				-2147483648	Why?

				-2147483648	One explanation is that estrus swelling incite male competition and females are likely to be inseminated by males best able to compete. Estrus swellings is a trait that increases the chance that a female’s offspring will be fathered by a fit competitor.

				-2147483648	In species where paternal care is crucial, estrus swellings would be counterproductive. In such species, males cannot be sure who their offspring are unless they remain close their mates. From an evolutionary view, females should be interesting in procuring a male who will provide long-term parental care. Males should be most interested in providing care to their offspring, not those of another male. To insure paternity, males in such species stay close to their mates.

				-2147483648	BUT what about humans? Like baboons we live in large groups where male competition is intense. Yet we do not have estrus swelling. Rather, ovulation is concealed. Humans are a big exception to the above explanation. The comparative method does not always provide a universal explanation.

				-2147483648	Infanticide

				-2147483648	There are two types of infanticide: (1) individuals, such as parents, kill related infants and (2) individuals kill unrelated infants. We shall discuss the second kind.

				-2147483648	Infanticide (continued)

				-2147483648	In harem polygynous species, such as some species of langurs, infanticide commonly occurs shortly after a new male takes over the harem. The best supported explanation is the sexual selection hypothesis: infanticide is a reproductive strategy of males. It is advantageous for males to kill infants of the previous harem male because females can become sexually receptive sooner if they are no longer nursing infants. Females have two counter-strategies. If they are pregnant by the previous harem male they can either fake out the male by sham estrus. If females have older infants, they may form coalitions with other females to deter the new harem male from killing their infants. The sexual selection hypothesis is an example of an explanation that views a traits as an adaptation of individuals NOT the group or species. Be sure you understand this! See the TA or instructor if you don’t.

				-2147483648	Case Study: Hanuman Langur

				-2147483648	Hanuman langurs live in harem groups (one dominant male, multiple females, juveniles) and bachelor groups (young males). During fights, the harem male, when old, is often replaced by a new male. The new male expels the old male, stays with the harem, and kills off juvenile langurs.

				-2147483648	Why?

				-2147483648	Pathology. Perhaps this behavior is maladaptive and a consequence of unnatural crowded conditions. Counterevidence: infanticide in hanuman langurs occur in natural uncrowded conditions.

				-2147483648	Cannibalism. Perhaps males kill juveniles in order to eat them. Counterevidence: langur males generally do not eat infants they kill.

				-2147483648	Sexual selection. Perhaps males kill juveniles as a reproductive strategy. Langur females are not sexually receptive when nursing offspring. When they stop nursing, they start ovulating. By killing unweaned juveniles, the harem male may be acting to return females to sexual receptivity so that he may reproduce. Supportive evidence: if a new male becomes the harem male, females who are pregnant will go into sham estrus. They will develop estrus swelling even though they are NOT fertile (they are pregnant with the offspring of the previous harem male). New harem males copulate with pregnant females during these periods of sham estrus. Females act as if they were duping males. The newborn was really fathered by the previous harem male but the new harem male refrains from killing as if he believes the newborn to be his. Sham estrus deceives males of an offspring’s paternity.

				-2147483648	FILM: Jane Goodall and the Wild Baboons of Gombe

				-2147483648	Highlights (understand italicized terms)

				-2147483648	Baboon troops have a dominance hierarchy. Each individual has a rank and behaves dominantly or submissively toward others. This hierarchy is revealed by play interactions among infants and juveniles. Among adults, displays and grooming interactions indicate an individual’s position in the troop. Grooming is the most important social behavior; it is the social cement of the troop reinforcing and establishing relationships.

				-2147483648	Examples of displays. Flashing eyelids are a mildly threatening display. The yawn display and the tail-in-face display are extremely threatening. Individuals either ignore or respond to the challenge. Females, who are smaller than adult males, may display threatening towards males but do not attack them.

				-2147483648	When a female is in estrus, males are attracted to her. One male attempts to keep other males away from the receptive female. Rivals display canines and flash eyelids towards the consort who tries to move the female away. Instructor’s comment: one hypothesis for the evolutionary function of estrus-swelling is that it attracts males.

				-2147483648	Infants, such as Angi, ride on their mothers’ back until 18 months old. Some females take an interest in the infants of other mothers. Mothers may be reluctant to allow females to carry infants. A female carrying a mother’s infant may be an alloparent (providing care) or may be kidnapping the infant. Instructor’s comment: infanticide is more common in one-adult male systems (harems) than in multi-male troops such as chimpanzees.

				-2147483648	Baboons eat a variety of food. Fruits, nuts, fish (from fishing nets), edible flowers, and occasionally meat. Baboons use stones as tools to scrap sticky fruit sap off their fur.

				-2147483648	Feeding and other situations often increase tensions in the troop. Frustrated males may attack subordinates. A single fight may cause a chain reaction of fights. (E.g., Fudge and Moses.) When tensions are high in the troop, males may kidnap an infant and carry her until tensions are reduced. In this fashion, males use infants as agonistic buffers. They are carrying infants not to protect them but rather so as to protect themselves. However, some males appear to take a benevolent interest in infants. For example, Moses was a male protector for Mango.

				-2147483648	Young male baboons leave their native troop and attempt to get into a new one. Stranger hanged on the periphery of Beach Troop for a week before attempting to get in. After a week of watching, he moved into the center of the troop and made intimating displays toward dominant males. Most males in the troop were agitated by Stranger who had the key ingredients of dominance, strength, size, and bluff. Two baboons formed a coalition against Stranger. Both males cooperated in attacking Stranger but failed to displace him. After enduring many such encounters, Stranger displayed submissively towards the dominant male of troop. The dominant male, who had remained aloof during the fights, acknowledged the gesture and Stranger became established in the dominance hierarchy.

				-2147483648	Film Highlights (continued)

				-2147483648	Why did Moses protect Mango? Two possibilities are kin selection and reciprocity. Moses may be the father of Mango; protecting the infant promotes Moses’ reproductive success (a kin selection explanation). Or Moses may be doing a favor for Marigold, Mango’s mother. In return, Marigold may be more cooperative towards Moses when she becomes sexually receptive (a reciprocity explanation).

				-2147483648	Recall that Stranger fought with two male baboons. These two male baboons formed a coalition. Coalitions are common in primate societies; they are a form of reciprocity. In chimpanzees, males remain in the group while females migrate. Probably as a result, chimpanzee coalitions are particular common and strong. Males in a chimpanzee community frequently form coalitions, patrol the periphery of their home range, and attack solitary chimpanzees from another group. Reciprocity and coalitions are extremely critical in human behaviors such as warfare. Perhaps the tendency of humans and chimps to form strong coalitions is attributable to similar selective pressures.

				-2147483648	Hominid Evolution

				-2147483648	Years Ago Species Comments Brain size

				-2147483648	~55 MY First primates Originated in North America and Europe which, at the time, were one continent.

				-2147483648	~30 MY First monkey-like primates

				-2147483648	~25 First ape-like primates From 20 to 5 MY, the Miocene period, explosion in ape diversity. Many ape species.

				-2147483648	~20-15 Proconsul Probably an ancestor of great apes and humans.

				-2147483648	~5 early Australopithecines Only teeth. Poor fossil record for apes, especially australopithecines.

				-2147483648	~3.7 Australopithecus afarensis AKA. Lucy. Bipedal but chimp-size brain. First found in Hadar region of Ethiopia. Males much bigger than females. 350-400 cc

				-2147483648	~2.3 Australopithecus africanus, robustus, boisei Africanus and robustus are found in south Africa. In east Africa, africanus and boisei fossils are found. Africanus has less robust features, boisei is extremely robust. Boisei existed till about 1 MY ago. Hence, australopithecines were living at the same time and place as species of Homo. 400-450 cc

				-2147483648	~2.0 Homo habilis First species in our genus. Once thought to be first tool-maker (habilis = “handy man”). But habilis existed at the same time as australopithecines so we do not know which species made which tools. 700 cc

				-2147483648	1.85 Homo erectus Earliest erectus find: THE BOY (WT1500). A 12 year old boy who, if matured, would be about 6 ft. Big brain as well as body size. Erectus first hominid to colonize Asia and Europe about 80000 years ago. Similar to us. 900 - 1200 cc

				-2147483648	200 000 Archaic Homo sapiens Archaic humans living in Europe are neanderthals. Controversy about their evolutionary history. Did they become extinct or did they interbreed with modern-looking sapiens?

				-2147483648	1400 - 1600 cc

				-2147483648	60 000-35 000 Modern-looking Homo sapiens Modern-looking humans probably originated in Africa but quickly appeared in Europe and Asia. Difficult to date their first appearance.

				-2147483648	Dating techniques

				-2147483648	Radiocarbon Dating. Good for 70000 to 1000 years ago. All living things have 14C. When organism dies, 14C decays at a steady rate (50% gone in 5000 years). Measuring the remaining 14C indicates how long ago the organism died.

				-2147483648	Fission-track Dating. Good for dating objects millions of years old. When 238U decays in obsidian it emits electrons which leave tracks on visible by electron microscope. The more tracks, the older it is.

				-2147483648	Fauna Remains. Paleontologists have a very good understanding of the evolutionary sequence of certain African animals, especially wild pigs and ungulates. They know which species lived when and where. You can get a good idea how old a hominid fossil is if you find it in the same layer as fossil remains of a particular pig species. Pig and other animal remains also indicates a hominid’s ecological niche.

				-2147483648	In these techniques, you are NOT dating hominid fossils directly. You are dating objects found in the same layer or strata as the fossil. It is critical that a site’s strata be distinct and undisturbed by rodents.

				-2147483648	Fossils are not bone! They are stone, mineralized remains of bone.

				-2147483648	Orangs, gorillas, and chimps.

				-2147483648	About 18 MY, first orang ancestors. It was once thought that chimps and gorillas are more related to orangs than humans. They are not. Orangs are distant cousins to humans, gorillas, and chimps. Gorillas and chimps are closer cousins to us.

				-2147483648	Australopithecines

				-2147483648	Footprints and Lucy skeleton. Australopithecus afarensis, Lucy, was bipedal but had a chimp-size brain. It seems that hominids were upright walkers millions of years before they had large brains.

				-2147483648	Hands. Australopithecine hands are similar to orangs in that they had long figures. They are very human-like but not fully modern-looking.

				-2147483648	Early tools. We are not certain which australopithecines made which tools and what tools were made by habilis. Nor are we certain how they were used. Archaeologists have used such tools in experimental butchering of giraffes. The tools’ sharp edge were sufficiently sharp enough to cut tough hides and scrap flesh from bones. Microscopic examination can indicate whether they were used to process plant remains.

				-2147483648	Afarensis skull. Lucy and other afarensis had chimp-size brains, about 350–400 cubic centimeters.

				-2147483648	Australopithecus africanus. Africanus were more gracile (delicate looking) than robustus or boisei. Australopithecus africanus, robustus, and boisei had a larger brains than afarensis. They had human-like teeth, a very slight gap between canines, and a U-shape dental arch.

				-2147483648	Robust australopithecines. Compared to africanus, robustus and boisei had broader faces, larger saggital crest (a ridge traversing the cranium), massive jaw muscles, huge molars. Their face and microscopic comparison of their teeth with living primates indicates their diet involved grinding plant remains. The boisei version, found in East Africa, were more robust looking than robustus (found in southern Africa). Boisei existed till about 1 MY ago and lived at the same time as habilis and erectus.

				-2147483648	Australopithecine footprints. Footprints, preserved by volcanic ash, are several million years old and are believed to be made by Australopithecus afarensis, an early human ancestor. They indicate that early humans (called hominids) were bipedal, walking upright, long ago.

				-2147483648	Lucy skeleton. Fossilized skeleton of A. afarensis (such as Lucy) indicates they were bipedal, short, had chimp-size brains, and were sexually dimorphic (females were shorter than males).

				-2147483648	Jaws. Australopithecine jaws are shaped more like chimpanzees than humans. Viewed from the top, chimp and Australopithecine jaws are U-shaped, humans jaws are shaped in a shallow arch. In addition, like chimps, australopithecines have large gaps between their canines.

				-2147483648	Robust australopithecines had massive cheekbones and a ridge running over the top of their skull (saggital crest). They lived after afarensis and were contemporary with gracile australopithecines (delicate skull features) and Homo habilis. Three human-like species living at the same time. Stone tools were also produced.

				-2147483648	Homo

				-2147483648	WT 15000. WT 15000 is the fossilized skeleton of a Homo erectus. It is thought to be of a 12-year old boy who, if fully mature, would be six feet tall. H. erectus lived after habilis and the australopithecines disappeared. They were the first hominids to leave Africa. In addition to having brains twice as large as chimps, later erectus had large brow ridges.

				-2147483648	Neanderthals. About 60000 years ago (BP or Before Present), humans living in Europe lacked chins, had large noses, very large brains, and probably buried their dead. Neanderthals were once thought to be brutish looking because of the reconstruction of one fossilized skeleton. Later, it was realized that the skeleton was of an arthritic and elderly individual. It is currently thought that Neanderthals would be inconspicuous among anatomically-modern humans of today. A central debate in paleoanthropology concerns the disappearance of Neanderthals and the appearance of modern-looking humans.

				-2147483648	WT15000. AKA “The Boy.” Extremely important find. 12-year old boy. Indicates erectus was tall; around 6 ft for mature adults (compare to afarensis females, 3.5 feet, and afarensis males, 5 ft.) Homo erectus had large brains (around 900 cc, gradually evolved to about 1200 cc). The Boy is dated to 1.85 MY ago, contemporary with Australopithecus boisei. Did erectus kill off boisei? Did erectus out compete them? Or were boisei unable to adapt to changes in their ecological niche? Also, why did erectus migrate out from Africa but not habilis or the australopithecines?

				-2147483648	Archaic Homo sapiens. One kind of archaic sapiens, Neanderthals, lived only in Europe (70000-40000 years ago), not Asia or Africa. Archaics living elsewhere are different from Neanderthals. Neanderthals where well adapted to cold conditions (Ice Age) in Europe. Big nose, no chins, brow ridges above eyes. Had fire, sophisticated tool kit, rock shelters, and hunted big game. Buried dead and may have believed in an after-life.

				-2147483648	Modern-looking Homo sapiens. Less robust facial features than neandethals and other archaics. Had chins. Probably first appeared in Africa but quickly then after in Europe.

				-2147483648	Questions for next class

				-2147483648	Why did hominids evolve big brains and sophisticated cultural systems and not dolphins or horses or pigs? Why and how did hominids become bipedal? And why did they become bipedal long before they had large brains? And why did big brains evolve at all? Under what conditions did natural selection favor big brains? Was diet a critical condition? Social competition? Lastly, what happened to archaic humans? Were they killed off by modern-looking humans? Out-competed? Or did they interbreed with modern-looking humans?

				-2147483648	Major issues in hominid evolution are the origins of bipedalism, big brains, concealed ovulation (loss of estrus), hairlessness. Competing hypotheses will be reviewed.

				-2147483648	All branches of anthropology are involved in investigating these issues. Archaeologists look at early tools to determine whether hominids were hunters or scavengers. Linguists are concerned with whether early hominids could talk and early language among archaic Homo sapiens. Ethnographers investigate contemporary hunter-gatherer societies that are probably similar (but NOT identical!) to early hominid societies.

				-2147483648	Cladogram

				-2147483648

				-2147483648	DNA techniques determine how identical the DNA strands of two species are. Techniques usually involve splitting DNA strands, putting a strand of each species together, and measuring the match-up of the strands. The more DNA strands match (joined pairs), the closer the two species are related, the closer their time of divergence. DNA techniques indicate that humans are more closely related to chimps than to gorillas. But the chimp-gorilla-human split is close, sometime around 9 to 6 MYA.

				-2147483648	Hominid Fossils

				-2147483648	(You don’t need to know all the fossil specimen numbers and site names but you should know the species and significance of Lucy, the Boy, the Black Skull, and general locations of fossils.)

				-2147483648	Early Australopithecines

				-2147483648	Lothagan teeth. Africa. 5.5 MYA. Oldest hominid remains. Probably australopithecine but fossil record is poor.

				-2147483648	Afar groups (AL333). Ethiopia. 3.7 MYA. Earliest best hominid remains. Probably 11 individuals killed at once. Cranial and postcranial (body skeleton) remains. of Australopithecus afarensis. Fair amount of sexual dimorphism (males, 5 ft, females, 3.5 ft.)

				-2147483648	Lucy. Ethiopia. 3.3 MYA. Nearly complete skeleton of Australopithecus afarensis. Fully bipedal but chimp-size brain (400 cubic centimeters).

				-2147483648	Laetoli footprints. East Africa. 3.8 MYA. No fossils, not clear what species. Footprints preserved in volcanic sediment indicate fully bipedal hominid.

				-2147483648	Later Australopithecines

				-2147483648	Lots of fossil from 2.5 to 1.3 MYA. At least three types of Australopithecines. Africanus and robustus in S. Africa. Africanus and boisei in East Africa. Africanus had less robust facial features than robustus and boisei. Boisei was very robust and jaw and teeth indicate a powerful grinder. Not much difference in brain size between gracile (africanus) and robust australopithecines (400-550 cc).

				-2147483648	Controversy about whether which of the later australopithecine is our ancestor. A robust Australopithecine fossil, WT17000, the “Black Skull” (not called black because of racial features, the fossil’s color is black), 2.5 MYA, shares key features which chimps which africanus lacks. One hypothesis is that the robust Australopithecines are not the direct ancestors of Homo habilis.

				-2147483648	Homo habilis. Larger brains than australopithecines; 700-1000 cc. Maybe two types. A big type (fossil ER1470), and a small type (ER1813). Hard to say which type, if either, was ancestral to erectus.

				-2147483648	Homo erectus. 1.85 MYA to 500,000 / 250000 (not clear cut when Homo erectus became Homo sapien). Good fossil, the Boy, WT15000. A fully bipedal, tall, big brain hominid. Indicates pronounced evolutionary trend towards big brains and increased height.

				-2147483648	Sometime between 1.8 MYA and 1.2 MYA, some erectus left Africa and colonized Asia. Important erectus sites are Sangiran, Indonesia, 1.3 MYA and Yuan-mou, China, about 1.2 MYA.

				-2147483648	Erectus shows gradual increase in brain size. Brain was 800-900 cc 1.5 MYA; 900-1000 cc about 1.2 MYA; 1100 cc about 0.5 MYA. Some people draw the line between erectus and our own species about 0.5 MYA by brain size. Others argue that it is difficult to distinguish erectus and archaic sapiens at this time.

				-2147483648	Earliest neanderthals about 250000 years ago. Neanderthals were in Europe AND the Middle East. Middle East sites are critical because it was a key migration area; lots of gene flow was channeled from Africa, Asia, and Europe in this area.

				-2147483648	Hot Topic: Origins of Modern-looking Humans

				-2147483648	When were the original ancestors for all humans? Some say, modern-looking humans originated recently, 200000-100000 years ago, in Africa and then spread to Asia and Europe replacing archaic humans. Others say that modern-looking humans evolved in different areas in the Old World. Everyone agrees that erectus was the first hominid to leave Africa. But some argue that multiple erectus populations throughout the Old World became modern-looking. Others argue that African erectus evolved quickly into modern-looking humans and replaced archaic humans in Europe and Asia.

				-2147483648	So is humanity’s earliest common ancestor Homo erectus about 1.2 MYA? Or modern-looking African humans, 150000 years ago? Recently mtDNA analysis has supported the latter view—that we are all descendants of a small group of Africans who lived 150000 years ago—BUT there are problems in mtDNA analysis. Unfortunately, we don’t have enough fossils to trace migration patterns from Africa to Eastern Asia. This is a hot area in paleoanthropology—more later.

				-2147483648	Hypotheses about Hominid Evolution

				-2147483648	The major issues in hominid evolution is explaining the origins of our bipedality, big brains, and sexuality (ventro-ventro copulation, concealed ovulation, menopause, long-term pair bonds). Other issues involve our hands, hairlessness, teeth, delayed maturation (human infants are very altricial—born helpless), social patterns such as male philopathy (males stay together, females transfer between groups). These traits make us special compared to other primates.

				-2147483648	(NOTE! Chimps are NOT our ancestors. Chimps and humans have been separately evolving millions of years. We are not their descendants. Rather, we are “cousins” sharing a common ancestors 9-7 million years ago.)

				-2147483648	What are the selective forces that shape our evolution? What’s the prime mover behind hominid evolution?

				-2147483648	The Tool-maker hypothesis. Darwin. Darwin guessed correctly that humans originated in Africa. Our closest relatives, chimps and gorillas, are found in Africa; he surmised that Africa was the home of our common ancestor. (Darwin’s contemporaries, reflecting a Euro-centric bias, believed that Europe was the original home of hominids.) Darwin proposed that tool-use (such as making weapons and hunting tools) led to increased intelligence, reduction in teeth, and increased social cooperation.

				-2147483648	Two problems with technology as the evolutionary driving force. First, some invertebrates demonstrate that brains are not the end-all in survival. They are costly and not always advantageous. Second, other species, including nonprimate species, make tools yet have small brains.

				-2147483648	Man-the-hunter hypothesis. Dart, Washburn, Lancaster proposed hunting, not tool-making, was the key factor in hominid evolution. Group hunting, they reasoned, requires cooperation, sexual division of labor, and sharing, activities which, in turn, demands significant level of intelligence.

				-2147483648	The hunting hypothesis, explicitly and implicitly, rested on the presumed male role in evolution and neglected the role of females. “Male” activities, such as hunting, were deemed critical, “female” activities negligible. However, in many contemporary hunting-gathering societies, males do not provide most of the food. Females provide a more stable supply of food by gathering.

				-2147483648	Woman-the-gatherer hypothesis. Tanner and Zihlman, partly in reaction to the Man-the-hunter hypothesis proposed that females played the central role in hominid evolution. Gathering requires knowledge of what plants are edible, how to locate them, when they are seasonally available, and how to process them. This requires a significant level of intelligence, hence, big brains.

				-2147483648	Schematic Hominid Evolutionary Tree

				-2147483648

				-2147483648	The robust australopithecines (robustus and boisei) are usually lumped in a separate branch from our ancestors because they share several traits with chimpanzees rather than to A. afarensis (Lucy). Robust australopithecines are probably not our ancestors. Also, at one time there were several species of hominids—two robust australopithecines and a species of Homo. This confuses our understanding of the archaeological record. We do not sure which hominid made tools, for example.

				-2147483648	It is difficult to decide when the H. erectus line ended and when the archaic H. sapien line began. It is also difficult to decide whether Neanderthals were ancestral to anatomically-modern humans. Much of our difficulty is due to our dating technology—we can’t date fossils with sufficiently high resolution.

				-2147483648	Hominid Evolutionary Trends

				-2147483648	Trends in hominid and human evolution are the evolution of big brains and bipedalism, as well as: hands (precision grip), long lifespan, increasingly helpless (altricial) offspring, sexual menopause and concealed ovulation, hairlessness, teeth, male philopathy (males stay in one group, females migrate), and large complex social groups. Hominid evolution is different from the evolution of other primates. There is only one hominid species left (us). Usually rapid evolutionary change is associated with speciation (recall adaptive radiation of lemurs). Why did hominids evolve rapidly leaving only one species remaining? Why did other hominid species go extinct?

				-2147483648	Hypotheses about Hominid Trends

				-2147483648	Tool-use hypothesis

				-2147483648	Darwin believed that early hominid tool-use led to increasingly larger brains which, in turn, lead to more complex tool-use. Bipedalism was favored by natural selection as it leaves hands free to carry tools especially hunting tools and weapons.

				-2147483648	Problem. We have a much better understanding of the hominid fossil record now than Darwin did. What do we know about Lucy that contradicts Darwin’s hypothesis? Despite being bipedal, Lucy and other australopithecines had small brains, not much bigger than chimpanzees. Bipedalism precedes large brains by at least a million years.

				-2147483648	Seed-eating hypothesis.

				-2147483648	Jolly, a primatologist, observed that geladas require good hands and good eye-hand coordination to pick up grass seeds which they eat. He suggested that early hominids occupied a seed-eating niche and their hands were pre-adapted to tool-use. Seed-picking hands later became good hands for tool-making.

				-2147483648	Problem. Jolly’s hypothesis may explain the evolution of precision-grip hands in early hominids such as the australopithecines but it does not account for later hominid trends such as big brains.

				-2147483648	Hunting hypothesis.

				-2147483648	Dart, Washburn, and Lancaster propose that early hominids occupied a hunting niche. To compensate for their physical disadvantages (slowness, small size, small canines), early hominids relied on cooperative group hunting. Cooperative hunting requires communication and intelligence, hence, big brains. Hunting also favored sharing of meat, sexual division of labor, and tools to process game. Experimental studies indicate that early hominid stone tools were sufficient to cut through the hide of large animals.

				-2147483648	Problems. (1) Why aren’t other cooperative hunters such as dolphins and wolves as smart as humans? (2) Electron-microscope comparisons of hominid teeth indicate that their diet was vegetable rather than meat-oriented.

				-2147483648	Gathering/collecting plants hypothesis.

				-2147483648	Rather than hunting, some researchers propose that gathering, particularly gathering by females, was the central force in hominid evolution. In most hunting-gathering societies today, gathering, not hunting, provides most of the calories. Gathering plants requires one to know which plants are edible and when, their location, seasonality, and how to eat them. This knowledge requires big brains. Bipedalism would be advantageous to carry gathered food.

				-2147483648	Problem. Other primates eat a wide variety of plants yet have small brains.

				-2147483648	Aquatic hypothesis.

				-2147483648	Elaine Morgan suggest that the ecological niche of early hominids was aquatic. Hominids were bipedal to keep their head above water. Other hominid trends, such as hairlessness, were consequences of aquatic-living.

				-2147483648	Problem. This hypothesis can be falsified—early hominids lived on savannas not in rivers or lakes.

				-2147483648	Mid-day hunting/scavenging hypotheses.

				-2147483648	Two hypotheses account for hominid traits as adaptations to hot savanna conditions. Bipedalism was advantageous because it minimized exposure to the sun’s heat. Upright-walking primates expose mainly the top of their skull to the full force of the mid-day sun. Quadropeds, such as baboons, expose most of their body. Hence, unlike other quadropedal species, bipeds can easily occupy a mid-day foraging niche.

				-2147483648	A related hypothesis offered by Dean Falk: when hominids became bipedal, a special adaptation improving brain cooling allowed some hominid populations to evolve bigger brains. Hominids without this special brain cooling system were unable to evolve big brains (which radiate a great deal of heat). Hominids with this special brain cooling system could forage during the mid-day heat and were able to out-compete hominids that had to stay in the shade.

				-2147483648	Problem. One problem is that we do not know if early hominids were able to forage during the mid-day. Also, Falk’s hypothesis makes dubious assumptions about the neural anatomy of early hominids and present-day humans.

				-2147483648	Home-base hypothesis.

				-2147483648	Isaac proposed that early hominids foraged differently than other primates. Other primates generally eat food where they find it. Hominids, Isaac suggest, had base camps from which they made excursions to collect food. They brought food back to these home camps. Bipedalism becomes advantageous because bipedal hominids can bring food back to base camps. Leaving infants at a base-camp and providing them with food also accounts for increasing helplessness of hominid infants (altriciality). Isaac’s hypothesis does not account for menopause, concealed ovulation, and other hominid trends.

				-2147483648	Problem. Insufficient fossil or archaeological evidence to falsify or support this hypothesis.

				-2147483648	Pair-bond/provisioning hypothesis.

				-2147483648	Lovejoy observed that humans produce more offspring than other primates because their interbirth interval is much shorter. (Chimps, 6–7 years; gorillas, 7; orangs, 8; foraging humans, 4-5 years). A short interbirth interval is evolutionary advantageous. Lovejoy proposes that males provisioning females in pair-bond relationships shortened interbirth interval. Females given food by males were able to produce more children during their reproductive period. Although it does not directly explain bipedalism and big brains, the hypothesis provides indirect support. Bipedalism would favor carrying food, hence, provisioning females by males. Provisioning females and their infants would allow infants to be more altricial. Increased in brain size is generally assumed to be associated with increased infant altriciality (helplessness).

				-2147483648	Problem. As with other hypotheses, we have more information about brain and bipedalism evolutionary trends but we don’t have sufficient information about the evolution of physical and behavioral traits such as pair-bonding, male provisioning and short interbirth intervals.

				-2147483648	Arms race hypothesis.

				-2147483648	Alexander’s hypothesis assumes that hominids became their own hostile force. He proposes: (1) hominids became ecological dominant such that other species (such as lions) were no longer serious threats or competitors; (2) the most important selective pressure was not any of the ones Darwin suggested (predators, food, climate) but group v. group competition; (3) the brain is a consequence of this social competition, it functions to solve social puzzles, play social chess, to produce what-if scenarios (e.g., what would he do if I do this to him).

				-2147483648	Given these propositions, one would expect a runaway arms race favoring increasingly big brains to deal with increasingly complex group competition. This hypothesis assumes that group v. group competition was progressively intense in hominids and that big brains are a consequence of this competition. As intergroup competition increases, hominid brains should become bigger.

				-2147483648	Alexander’s hypothesis accounts for another evolutionary trend besides brain size: why only one hominid species remains today (H. sapiens). Other hominid species, such as the robust australopithecines, were presumably unable to compete with hominid groups. The hypothesis also suggest that big brains are an inevitable product of group competition. Group competition occurs in chimps; if humans were removed from their environment and if they were given several millions years to evolve, chimps may have evolved brains as large as humans.

				-2147483648	HOMINID EVOLUTION—Evolutionary Hypotheses (review)

				-2147483648	Hunting hypothesis. Further counterevidence: Under a pure rigid interpretation of the hunting hypotheses:

				-2147483648	IF natural selection strongly favored hominid hunting skills (communication, cooperation, prey prediction) AND…

				-2147483648	IF males exclusively hunt THEN…

				-2147483648	One should see sexual dimorphism in brain size. Males should have larger and more intelligent brains. Since proportional brain size is equal among the sexes, the hunting hypothesis is not supported.

				-2147483648	Alexander’s social competition hypothesis. Brief review: since hominids became ecologically dominant, competition among groups became hominids main “hostile force” (most powerful selective pressure). Intergroup competition was the selective pressure leading to increased intelligence, consciousness, self-awareness. This hypothesis is not limited to humans. Species with intense intergroup conflict should also be highly intelligent and self-aware (example: chimps).

				-2147483648	If males are the primary participants in intergroup competition, why don’t they have bigger brighter brains than females? Presumably because females also engage in competition, perhaps competition among females.

				-2147483648	Evolutionary Hypothesis about Human Sexual Uniqueness

				-2147483648	Humans differ from other primates, and most other species, by their concealed ovulation and menopause (cessation of ovulation around 45 to 50 years).

				-2147483648	Menopause

				-2147483648	From an evolutionary view, why do women stop reproducing? And why do women live after menopause. Why should selection favor women to survive beyond their reproductive period?

				-2147483648	Species-level explanation.

				-2147483648	Women who reproduce in their later years are more likely to produce infants with birth defects (i.e., Down syndrome: a chromosomal abnormality). It is an advantage for the species to keep “bad genes” out of a species gene pool. Selection favored women to stop reproducing in their later age.

				-2147483648	Problems: Why didn’t selection favor women who could reproduce a long time without the risk of producing “bad genes” offspring? Also, are such infants threats to the gene pool? Will they be viable and live to a reproductive age? And why do women live well after they stop reproducing?

				-2147483648	Post-reproductive child care.

				-2147483648	If a women has a child at 45, she still has to care for her or him for many years, otherwise the infant will die. Also, women provide significant care for grandchildren. Perhaps natural selection favored women’s post-reproductive life because of the significant care they provide to their children as well as their children’s children. This explanation is more widely accepted than the previous one.

				-2147483648	Elephants have something similar to menopause and, not unexpectedly, post-reproductive females have active roles in elephant society.

				-2147483648	Concealed Ovulation

				-2147483648	Other species don’t “advertise” ovulation. However, all species but humans have some indication that they are ovulating. For example, gibbon females lack estrus swellings but emit pheromones. Why do human females conceal ovulation not only from others but from themselves?

				-2147483648	Pair-bond maintenance hypothesis.

				-2147483648	Females keep males around (maintain pair-bonds) by having sex all the time. If females had estrus swellings, males would only hang around during estrus times. If females concealed ovulation, males would be continually interested in sex.

				-2147483648	Prostitution hypothesis.

				-2147483648	Females elicit assistance from males by sex (food-for-sex). If females concealed their ovulation, males would be more continually interested in sex and provide a stable amount of food.

				-2147483648	In bonobos, estrus swellings last 20 or more days; in chimps, about a week. Bonobos are more sexually active than chimps and bonobo female-male relationships are stronger than male-male relationships. In chimps, male-male relationships are stronger than female-male relationships. There is some support, then, that sexual activity is related to strength of female-male relationships.

				-2147483648	Problems. Why should selection favor daily sex during non-fertile periods, a tremendous waste of energy?  Also, gibbons have strong pair-bonds but they don’t copulate daily.