It can be difficult to imagine how complicated organisms have come about without some designer being involved. Even Darwin understood that it is difficult to see how an organ as complex as the human eye, with a pupil that regulates light, a lens that can flex to focus at different distances, and the sophisticated nervous tissue of the retina, could have evolved through the process of natural selection. But he did conceive of how it was possible.

You might hear critics of evolutionary theory make a statement like this:

The human eye is too complex to have evolved by chance from nothing.

Questions

1. Where does the variation that natural selection acts on arise from?
2. Scientists estimate that each individual has three “new” mutations that could affect their anatomy and physiology. In a population of only 10,000 people and using our low estimate of mutations that could be subject to selection, about how many “new” variants of genes appear every generation?
3. Question 2 gives you a sense of how much genetic variety appears by chance. Is natural selection “chance”?
4. Consider the evolution of pigeon neck ruffs discussed in the chapter. What did these neck ruffs evolve from?
5. Some simple single-celled organisms can sense light and will avoid it (or move toward it). Do these organisms have eyes?
6. Simple animals, such as earthworms, can change the shape of parts of their bodies, like their mouths. Is it possible that the same mechanisms that change mouth shape could change lens or pupil shape?
7. Reflect on your answers to questions 1–6. Explain why the statement bolded above sounds right, but isn’t.