Endless Forms The Evolution of Gene Regulation and Morphological Diversity
diversity and the long span of time (.540 million years) “...we are always slow in admitting great changes of since their divergence from a common ancestor. Simiwhich we do not see the steps... The mind cannot possilarly, most protostomes and deuterostomes, with the bly grasp the full meaning of the term of even a million exception of the vertebrates (which possess four or years; it cannot add up and perceive the full effects of more clusters), possess roughly equivalent clusters of many slight variations, accumulated during an almost Hox genes that must date back to at least their last infinite number of generations.” common Precambrian bilaterian ancestor (de Rosa et —C. Darwin, The Origin of Species (1859) al., 1999). Since cnidarians (jellyfish, sea anemones) and