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Evolution in Action. Perhaps the best way to understand evolution is to watch it in action. Biology abounds with interesting studies of species undergoing evolutionary change. Few natural populations, when carefully examined, are not responding in one way or another to natural selection. These six, concerning bacteria, lizards, birds, dogs, and cats, are but a few of the many examples that you might explore.

1. Did Darwin get it wrong about Galápagos finches?
2. Why do tropical songbirds lay fewer eggs?
3. Evolution of the family dog.
4. DNA and Darwin: Lizard evolution repeats itself.
5. How E. coli bacteria became deadly: Making a monster.
6. Bird-killing cats may be nature's way of making better birds.

The Evidence for Evolution
At its core, the case for Darwin's theory of evolution by natural selection is built upon three pillars: first, evidence that natural selection can produce evolutionary change; second, evidence from the fossil record that evolution has occurred; third, evidence of evolutionary descent in the DNA sequences of the genomes of different species. In addition, information from many different areas of biology — including areas as divergent as embryology, anatomy, and ecology — can only be interpreted sensibly as the outcome of evolution.

Arguments Against Evolution
Of all the major ideas of biology, the theory that today's organisms evolved from now-extinct ancestors is perhaps the best known to the general public. This is not because the average person truly understands the basic facts of evolution, but rather because many people mistakenly believe that evolution represents a challenge to their religious beliefs. Although highly publicized criticisms of evolution have occurred ever since Darwin's time, the scientific community has found the objections to be without merit.

Do Some Genes Maintain More Than One Common Allele in a Population?
A population of bacteria contains variation among its members that arises as a result from random mutations. It is expected that variants will arise in a population, but the fact that they are maintained in the population in significant numbers is not expected. Theory predicts that whenever a new variant appears in a population, it will be weighed in the balance by natural selection and either win or lose. One version of the gene should become universal in the population, and the other be eliminated. But contrary to simple theory, natural populations of most species, including bacteria, appear to have lots of common variants — they are said to be "polymorphic." How does a polymorphic condition arise in a bacterial population, and how can it be maintained? To investigate this experimental question, Julian Adams and co-workers at the University of Michigan set out to see if polymorphism for metabolic abilities would develop spontaneously in Escherichia coli (E. coli) bacteria growing in a uniform environment, and, if polymorphism arises, to investigate how it is maintained in the population.