Genes and evolution

The mechanisms of DNA change that we have surveyed in this chapter help to explain how organisms have diverged so dramatically since the origin of life. The result is the incredible diversity of species in the modern world. Nevertheless, species that appear to be very different still have a remarkable amount of DNA in common. It is well known that we share more than 99% of our DNA with chimpanzees and scarcely less with gorillas, but it is a less familiar fact that we share 50% of our genes with bananas and 30% with baker's yeast.

Some of the genes that seem most clearly associated with multicellularity seem - surprisingly - to have originated in protists. Examples include hormone and hormone receptor genes. In large animals such as humans, a hormone is made in one specialised part of the body and dispatched to others, where it alters specific activities in target cells. What use are such devices in protists? What good are insulin and insulin receptors to amoebae? Whatever these gene products do in protists, it is obviously not the same thing that they do in mammals. During evolution, it seems, proteins can be recruited to different uses depending on the requirements of the organism. But to date, this fascinating topic has not been sufficiently researched to provide us with general answers.

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