You Can Never Go Back Home

ScienceDaily has a report of research from the University of Oregon in which it has been shown that evolution is a one-way trip. The author writes:

The team used computational reconstruction of ancestral gene sequences, DNA synthesis, protein engineering and X-ray crystallography to resurrect and manipulate the gene for a key hormone receptor as it existed in our earliest vertebrate ancestors more than 400 million years ago. They found that over a rapid period of time, five random mutations made subtle modifications in the protein's structure that were utterly incompatible with the receptor's primordial form.

This seems to indicate that once evolution in a species has proceeded down a particular path, it doesn't go back. Once upon a time, the ancestors of humans had four premolars (bicuspids, if you are a dentist). We now have two because the first two have been lost along the way. I remember my advisor Fred Smith remarking once upon a time that once a trait has been lost evolutionarily, it never comes back. A species might follow a different path than the one it originally took to get to a similar place, however. This explains why whales and icthyosaurs don't look the same, even though they are both exploiting an aquatic niche. Read the whole thing.

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