MICROEVOLUTION

notes
 
 
 
 

Evolution in action?
 

  Micro-1




"All that is needed to prove evolution is observed microevolution added to the philosophical doctrine of uniformitarianism which (in the form that is needed here) underlies all science"

        M. Ridley  Evolution and Classification
 

"Natural selection may only subtract, but mutation can add."

        R. Dawkins, p 169  The Blind Watchmaker
 

"...truly new genetic information is not constituted by new alleles (alternate expressions of a gene) but by genes with a uniquely different structure and function."

         Lester and Bohlin, The Natural Limits of Biological Change ,  p 88.
 
 
 
 
 
 

GOALS:
 

Understand what is meant by "biological information"

Does natural selection act on genetic variation to produce adaptations (directly observable) on some small scale? (yes)

What are the genetic mechanisms?

What is the relevance of this for the Creation/Naturalism debate?

Understand the qualitative difference between microevolution and macroevolution

Recognize that genetic variation and adaptation are part of God's creation
 
 
 
 
 
 
 

 OUTLINE:
 
1. Definitions of microevolution

2. Genetic information - what is it, how is it stored and processed?

3. Overall mechanism - Natural selection acting on genetic variation

4. Examples of microevolution

 A.  Examples involving same level or loss of genetic variation

 B.  Examples involving increase in genetic variation

5. Most significant changes for which there is direct evidence

 
 
 

1.  Definitions:
 

"small-scale evolutionary phenomena"
        Curtis and Barnes, Biology, pg 962.
 

"diversification within a given type"
        Percival and Kenyon, Of Pandas & People, pg 11.
 

Evolution in action, flies in bottles, shift in gene frequencies:

"we have abundant, direct, observational evidence of evolution in action, from both field
and laboratory."
        S. Gould, "Evolution as Fact and Theory", Hen's Teeth and Horse's Toes

"Orthodox NeoDarwinians extrapolate these even and continuous changes to the most
profound structural transitions in the history of life.  ...Macroevolution (major structural transition)
is nothing more than microevolution (flies in bottles) extended.  ... The shift in gene frequencies is
an adequate model for all evolutionary processes - or so current orthodoxy states."
        S. Gould,  The Panda's Thumb, pg 187.
 

Capacity of an existing genotype to vary within limits.
"Grasse argued that ......the real problem of evolution is to account for the origin of new genetic information, and it is not solved by providing illustrations of the acknowledged capacity of an
existing genotype to vary within limits."
        P. Johnson, Proceeding of a symposium "Darwinism: Scientific Inference of Philosophical Preference", Mar. 26, 1992, SMU

 

2.  What is a genetic information and how is it stored and processed?
 

 gene:  segment of DNA which codes for a protein
 
 

  Micro-2



 
 

 order of nucleotides in DNA determines order of amino acids in proteins

 order of amino acids in proteins determines 3-D structure

 3-D structure of protein determines function

 order of nucleotides in DNA  =  information
 
 


Micro-3       Micro-4       Micro-5      Micro-6




 chromosome pairs, dominant and recessive alleles
     (alleles  =  different forms of a gene)
 
 

  Micro-7




 typically:

  a gene effects more than one trait
  a trait is effected by more than one gene
 Ex.  "some of the genes that affect bristle development (in flies) also affect reproductive organs"
      D. Futuyma, Science on Trial, pg 129.
 
 
 
 
3. Overall mechanism of microevolution - natural selection acting on genetic variation
 
 

     Natural selection:

"...any consistent difference in survival or reproduction between genetically different members of a species."
        D. Futuyma, Science on Trial, pg 116.

"...whenever a gene can bequeath more copies of itself to subsequent generations than any other gene,
it takes over."
        D. Futuyma, Science on Trial, pg 116.

= nonrandom death
 
 

    Non-tautologous formulation:

 
If:
a)   different members of a population vary in trait "q"
       (condition of variation)

b)   leave different numbers of offspring due to presence of trait "q"
            (condition of selection)

c)   transmit trait "q" faithfully from parents to offspring
            (condition of heredity)


Then:

the frequency of trait "q" will differ between the population of all parents and all offspring

 

    Types of selection:
 

1.  stabilizing selection (conservative) - rejects deleterious mutants
 

2.  balancing selection (conservative) - maintenance of two or more genetic variants at frequencies higher
     than can be accounted for by random processes.

Ex. Sickle-cell anemia in malaria infested areas


3.  directional selection (adaptive) - brings a population to the most adapted state, genetic structure of a
    population changes over time.

new environment, new favorable mutations


4.  sexual selection  -  "evolution that is based purely on superior reproduction",
                                    D. Futuyma, Science on Trial, pg 121.

male peacock's train of feathers


5.  kin selection (descriptive, hand waving?)

"because close relatives inherit the same genes from their ancestors, a gene that influences an individual to help its relatives can therefore improve the survival of the other copies of that same gene which the relatives carry."
        D. Futuyma, Science on Trial, pg 121.

honey bees (workers), sterility and suicide

 

Does natural selection have the ability to create?
 

passive versus active

subtracts by selecting only a portion of the existing gene pool

sculptor creates by subtraction?
 
 
 
 

4.  Examples of microevolution
 
 
A.  Examples involving same level or loss of genetic variation

         (Natural selection acting on existing genetic variation)

 
"Genetic diversity is an advantage to a population.  ...Combinations of both expressed and unexpressed genes (in the genetic reserve) can give biological populations adaptive potential."
        Davis and Kenyon, Of Pandas and People, pg 75

 
Mechanisms of genetic variation (shift in gene frequency or gene combinations)
"Random assortment and recombination provide a mechanism for maintaining variability and new combinations.  ...New combinations of genes or chromosomes are constantly formed."
     Lester and Bohlin, Natural Limits of Biological Change, pg 57
Random assortment- sorting of maternal and paternal chromosomes
 

Recombination (crossing over) - exchange of alleles between homologous chromosomes, produces new gene combinations

 
 

Micro-8


Genetic drift - "a change in the gene pool that takes place as a result of chance"
        Curtis & Barnes, Biology, pg 983.
 

Founder effects and bottlenecks

 - small (nonrepresentative) portion of gene pool is isolated

 - inbreeding can reveal hidden characteristics     (Ex. Amish - short fingers, short stature, sixth finger, blood disease)

 -can lead to rapid rate of change


Fixation
 
 
 

 
Examples:
 
"If we want absolutely bona fide evidence for the reality of microevolutionary change and speciation in nature, the cases of the circumpolar overlaps and the fruit fly of Hawaii come very close ..."
        M. Denton, Evolution:  A Theory in Crisis, pg 83
1.  circumpolar overlaps (Gulls)
 
 

Micro-9





2.  unique but related species of Hawaiian fruit flies on various islands
 

3.  unique but related species finches in Galapagos Islands
 
 

Micro-10




4.  unique but related species of tortoises in Galapagos Islands
 

5.  finch beaks ("evolution in action")
 

6.  industrial melanism
 
 

Micro-11



7.  English sparrows in US

Micro-12




8.  artificial selection (dog breeding)
 
 

  Micro-13




9.  Madeira rabbits
 

10.  humans - skin color, mongoloid eye, short stout eskimos, tall thin africans
 
 
 

 Speciation:
"it is no exaggeration to say that if no instances of uncompleted speciation were discovered the whole theory of evolution would be in doubt."
         T. Dobzhansky, Amer. Sci., Dec. 1957, p 388.
 

"Natural selection has been directly observed and there can be no question now that new species do originate in nature; furthermore, it is now possible to explain in great detail the exact sequence of events that lead to species formation, ..."
         M. Denton, Evolution:  A Theory in Crisis, pg 85.

Reproductive isolation
physical barrier
breaking up of a breeding chain
ecological isolation (fruit flies on Hawthorn and apple trees)


Is speciation macroevolution?
 
 


 

B.  Examples involving an increase in genetic variation

          (new alleles or entirely new genes)
 
 

i)  Mechanism for increase in genetic variation:  mutations
"Mutations are generally regarded as the raw material for evolutionary change"
        Curtis & Barnes, Biology, pg 982.

"...mutation provides the variability among organisms that is the raw material for evolution."
        Curtis & Barnes, Biology, pg 247.

"Natural selection may only subtract, but mutation can add"
         R. Dawkins, The Blind Watchmaker, pg 169

"Mutation is, ultimately, the source of new genetic variations, and without genetic variations there cannot be genetic change.  Mutation is therefore necessary for evolution. "
         D. Futuyma, Science on Trial, pg 136.

"The Darwinian explanation is that earlier stores of information are elaborated by extensive random mutations, and that resulting "enriched" gene pools are then weeded out by natural selection."
        Percival and Kenyon, Of Pandas and People,  pg 85.

The origin of genetic variation (macroevol.) - gene duplication + mutations.
         Curtis & Barnes, Biology, pg 988
 


        Mutations can be directly observed

"Now the only way we can know that a genetic variation is a new mutation is to see it arise in a genetically uniform population, ..."
    D. Futuyma, Science on Trial, pg 138.
 
 
        Important questions about mutations:
 
1. What are they?  (Types of mutations)

2. How pervasive are they?

3. Do beneficial mutations exist?

4. What can mutations do?  (Can mutation + natural selection create?)

5. How did present level of genetic variation arise?
 
 
 

        Types of Mutations
 
1.  point mutations  (increases diversity of alleles)
 occurs during DNA replication
 change, addition, or deletion of a single nucleotide in DNA
 can affect the sequence of amino acids in protein
 can change entire structure and function of protein
2. chromosomal mutations (change in the sequence of genes on affected chromosomes)

         (different from recombination in that order of genes on a
            chromosome is affected)

 a segment of a chromosome may be duplicated
 one or more chromosomes may be fused
 a segment of a chromosome may be deleted
 a segment of a chromosome may be inverted
 a segment of a chromosome may be transferred to
        different position on the same chromosome
 a segment of a chromosome may be transferred to an
         entirely different chromosome
         (all have been observed in Drosophila)
 
 
        Prevalence
     rare for any particular gene  (10-5 per gene per generation)

     but many genes per organism, many organisms per population

     humans:  ~ 2 new mutations/person, 8 x 109 in present population
 
 

        "good" versus "bad" mutations
 
    Only a small fraction lead to large changes - usually harmful
 

    Most have small effect:

 1)  adaptively neutral
  protein shape not altered, noncoding DNA sequences, etc.


 2)  adaptively beneficial

"good" or "bad" depends on environment

"Many mutations in fruit flies, plants, and other organisms are known that increase or decrease the activity of enzymes and proteins to a greater or lesser extent....In fruit flies, for example, most mutations cause slight increases or decreases in rate of growth, body size, the length of wings or legs, the number of bristles, the ability to detoxify DDT and other poisons, and so on."
        D. Futuyma,   Science on Trial, pg 136
 
 
 

            How did present level of genetic variation arise?
 
A.  created by God

B.  arose by mutation over time

C.  some combination of A and B
 


 
ii)  Examples
 

    A.  Generation of new alleles
 
 

 1.  Drosophila (fruit flies)
 
 chromosomal map

 Micro-14



hybrid pop. adapts more rapidly than parent pop.,  wing length, mating behavior, sensitivity to temp., rate of growth, body size, ability to detoxify DDT,  bristle number, ethanol vapor resistance, legs growing out of head instead of antennae
 
 

 Micro-15



 Johnson-Provine debate:
 

new organs?

different species are further apart from each other genetically than humans are from chimpanzees?

 
"Fruit flies refuse to become anything but fruit flies under any circumstances yet devised."
         Francis Hitching, "The neck of the giraffe:  Where Darwin went wrong", 1982, p. 56-57.
 
 
2.  Sickle-cell anemia in malaria infested areas  (point mutation - malaria resistance)
S allele:  hemoglobin-A  (normal)

s allele:  hemoglobin-S,  differs in only one position from A, reduces ability of red blood cells to carry oxygen
 

both alleles retained:

ss - severely anemic (usually fatal)

SS - susceptible to malaria

Ss - not anemic, resistant to malaria
 
 
 


 3.  Resistance of insects to insecticides

 
different mechanisms:
i)  modifying an existing enzyme to enable it to break down DDT

ii) produce more enzyme that breaks down DDT

iii)  slow down penetration of DDT into cell through altered cell membranes


 

 "At least 225 species of insects are now resistant to one or more insecticides.  One species is even able to remove a chlorine atom from a DDT molecule and use the remainder as food."
         Curtis and Barnes, Biology, Curtis and Barnes, pg 964.
 
 
 

 4.  Resistance of bacteria to antibiotics
 
"What caused this resistance?  Changes in the metabolism of individual bacteria or changes in the bacterial population - that is, evolution? ....  Like the black moths and the cyanide resistant scale insects, they were simply variants produced by chance in the original populations and selected by their environment"
         Curtis and Barnes, Biology, pg 964.
 

"In both bacterial antibiotic resistance and pesticide resistance, the populations possessed the enzymes and metabolic processes at a low activity before exposure".
         Lester and Bohlin, Nat. Limits to Biol. Change, pg 103.
 
 

Mechanisms of developing resistance:

 C. M. Henry, Chem. & Eng. News Mar 6, 2000 p 41;  S. Levy, Sci Amer. 1998, vol. 398;  J. M. Smith, Nat. Hist. 6/94 pg 39.
 

a)  alter drug's target

b)  prevent drug from reaching target

c)  destroy or modify the drug so it cannot bind to target
 
 

 Micro-16     Micro-17

 
Resistance can be acquired through
i) genetic mutations
ii) acquiring resistance genes from other bacteria via plasmids
 
 
 
 5.  Other bacteria experiments
cell size in E. coli   Science, 272, 1802, (1996).
 
 

 Micro-18

 
"Four years later, the team had amassed a freezer full of data on how the bacteria had evolved over an impressive 10,000 generations - long enough to see evolution in action."
        Science 272, 1741, (1996).
 

Even Eldridge is dubious about overextrapolating from this bacterial experiment.  ....As Gingrich put it, "I don't think we can generalize from this to mammals.  But Riley.... thinks such extrapolation is valid.  She argues that no matter what the organism or the scale, the same evolutionary forces are at work, albeit with different strengths."
          Science  272, 1741,  (1996).
 
 
 

"What is the use of their unceasing mutations if they do not change?  In sum, the mutations of bacteria and viruses are merely hereditary fluctuations around a median position; a swing to the right, a swing to the left, but no final evolutionary effect."
     Pierre Grasse, Evolution of Living Organisms, 1977, pg 87.
 
 
 

“Throughout 150 years of the science of bacteriology, there is no evidence that one species of bacteria has changed into another.”
        Alan Linton,  Emeritus Prof. of Bacteriology, U. of Bristol, in The Times Higher Education Supplement, April 20, 2001, pg 29.
 
 
 

B.  Generation of truly new genes (entirely different category of structure or
    function)
 
 
The origin of genetic variation (macroevolution) -  gene duplication + point mutations
         Curtis & Barnes, Biology, pg 988
"It is believed the ancestral gene - coding for the  ancestral protein - was accidentally duplicated several  times in the course of evolutionary history and that  these duplicates were preserved by unequal cross-over  events.  Once the genes were duplicated, mutations  led to their divergence, eventually giving rise to the  present family of genes."
        Curtis & Barnes, Biology, pg 367.
 
 

"Although genes evolve whether duplicated or not, the  addition of new information requires duplication.  In the  complex organisms living today and for a long time into  the past, the primary source of new genetic material  (new information) must be duplicated copies of existing  genes, since the creation of a new useful gene seems  impossible."
       Markert, Shaklee, and Whitt, "Evolution of a gene",  pg 112
 

List of examples of gene duplication + point mutations producing a truly new gene with an entirely different category of structure and function:
none to my knowledge!

has exon shuffling ever done this?

families of related genes (myoglobin/hemoglobin family) are cited as evidence of this, (assumed, but not observed)
 
 
 
 

 5.  Most significant changes for which there is direct evidence
 
"The only observational evidence we have so far contradicts the possibility that mutations can produce a truly new gene, a nonallele in a new category of structure and function."
         Lester and Bohlin, Nat. Limits. of Biol. Change,  pg 87

"There is no evidence mutations create new structures.  They merely alter existing ones."
         Davis and Kenyon, Of Pandas and People, pg 11.
 
 
 

              -bacteria acquiring ability to metabolize effluent from nylon factory

                    (Proc. Natl. Acad. Sci.  vol 81, 2421, 1984)

                    mutation leads to a shift in reading frame that produces an enzyme which can
                    metabolize molecules in the effluent
 
 

 -Barry Hall's work on changes in a lactose metabolizing system
see    http://www.arn.org/docs/behe/mb_trueacidtest.htm
        http://www.arn.org/docs/behe/mb_responsetokmiller0101.htm
          (adaptive mutations?)
 
 -cave mutants (loss of function)
 


 Micro-19


 -enzyme evolution (industrial processes)
 
 
 

-others?
 
 
 
 
 
 
 

Summary
 
A tremendous amount of variation, adaptation, even speciation, can occur due to existing genetic diversity

Much of present genetic diversity (different alleles and gene combinations) has arisen by mutation

Organisms are created by God with a tremendous ability to adapt

Microevolution via selection acting on genetic variation (random assortment, recombination, mutations) is an observed fact

There are no observations of the creation of new genes with entirely new categories of structure or function

Gene duplication + point mutations is the mechanism proposed by evolutionists to account for macroevolutionary change, but no direct observations of this exist.
 

None of the examples you hear about can be considered an elementary step in a macroevolutionary process!
 
 
 
 
 

"The three examples we have just considered (industrial melanism, insecticide resistance and drug resistance in bacteria) are among the many that support Darwin's proposal that natural selection is the mechanism of evolutionary change.  In themselves, however, they do not provide evidence for macroevolution - that is, evolutionary change above the level of species.  ...  ".
        Curtis and Barnes, Biology, pg 965.
 

"Darwin's assumption that the tree of life is a consequence of the gradual accumulation of small hereditary differences appears to be without significant support.  Some other process is responsible for the emergent properties of life, those distinctive features that separate one group of organisms from another. ... Clearly something is missing in biology."
        Brian Goodwin, How the Leopard Changes its Spots,1994, viii-ix.
 

"We can go on examining natural variation at all levels ... as well as hypothesizing about speciation events in bed bugs, bears, and brachiopods until the planet approaches oblivion, but we will still end up with bed bugs, brachiopods, and bears.  None of these body plans will transform into rotifers, roundworms, and rhynchocoels.  In order to find out why they will not, we need to ask much more interesting questions than those of allelic changes and speciation events."
        G. L. G. Miklos, Mem. Ass. Australas. Palaeontols. 15, (1993) pg 7-41.
 

"All environments, inevitably, do change.  The secret of life is that it can change with them and continue to thrive, and if I were searching for signs of an infinitely wise creator, I might find them here."
        Douglas Chadwick, Evolution Right Before Their Eyes, 1994.
 
 

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