The bicycle instruction book contains a list of steps, in order, describing how to put the bicycle together. Steps sometimes refer to each other ("Add the front wheel to the front fork you made in step 10.") so that we can keep track of the sub-assemblies we've already made. It also contains diagrams to make assembling the bicycle easier. The instruction book is also divided into chapters, one for each major group of components, so that we can assemble the bicycle in stages. After following all the instructions, we end up with a bicycle.

Life's instruction book is a bit different. The steps are scrambled around in the book. The steps can't talk about each other. There are no diagrams, nor are there any chapters. And at the end, not only do we need to have made the organism, we need to have copied the instruction book, too, or the organism can't pass its instructions on to its children. With such a mess for an instruction book, how do living things manage to do anything at all?

The key is that they have different kinds of instructions that not only tolerate having a disorganized instruction book, but actually take advantage of it. To see how this works, let's look at an example.

In the bicycle instruction book, the steps for putting the pedals on the crank are:

1. Find the crank, the pedals, the pedal bolts and the pedal washers. You'll need a wrench for this job.
2. Put a washer on the right crank arm.
3. Put the right pedal on the right crank arm.
4. Insert a bolt into the hole in the right crank arm and tighten it with a wrench.
5. Do the same things for the left pedal and pedal arm as in steps 2 through 4.

If life's Instruction Book included instructions for this, it would look like:

• Tighten any loose bolts with a wrench.
• Put a pedal on any crank arm that has a washer on it.
• Put a bolt in the hole of any crank arm that has a pedal on it.
• Put a washer on any crank arm that doesn't have one.

How does Life follow such instructions? In carrying out the genetic instructions written in their Instruction Books, living things don't act much like single individuals. Instead, they act rather like factories containing huge numbers of workers. Life follows its Instruction Book by assigning one instruction to each of its many workers, and having them try their assignments all at once. Each of the workers is a protein, and the instruction it's carrying out is a gene. How do living things assign workers to instructions? How do living things know what instructions to carry out? The answers to these questions are the keys to how to read Life's Instruction Book.