Comparative Genomics and the Evolution of Animal Diversity

At the end of his book, On the Origin of Species, Charles Darwin speculates that all animals arose from a common ancestor. It has been suggested that at a remote time in the past, perhaps 600 million years ago, a flat worm lived in burrows beneath the ancient oceans. Over the course of many millions of years of evolution, this creature spawned the remarkable diversity we now see among modern animals.

There are 25 different animal phyla; each phylum represents a basic type of animal {Figure 19-1). For example, annelids are composed of simple repeating body segments, whereas many mollusks are twisted or coiled (consider snails, for example). In terms of sheer numbers and diversity, the arthropods are the most successful animal phylum. They include sea creatures such as horseshoe crabs, lobsters and shrimp, as well as land animals including insects, centipedes, and spiders. Many members of this phylum can fly. Where did all this evolutionary diversity come from? We are just starting to get some answers.

Most animal phyla fall into three major groups: the lophotro-chozoans, ecdysozoans, and deuterostomes (see Figure 19-1). (In earlier times, the lophotrochozoans and ecdysozoans were Called, collectively.

Most Animals Have Essentially the Same Genes(p 614)

Thiee Ways Gene Expression Is Changed during Evolution {p. 619) *

Experimental Manipulations that Alter

Morphological Changes in Crustaceans and Insects {p. 630) »

Genome Evolution and t luman Origins (p. 635)

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* flanish rcurMl worfn (ancestor}

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