Monday, November 06, 2006

Dolphins sprout legs?

Uncommondescent blogged about the find of a dolphin that had an extra set of fins.

From above article:
Japanese researchers said Sunday that a bottlenose dolphin captured last month has an extra set of fins that could be the remains of hind legs, a discovery that may provide further evidence that ocean-dwelling mammals once lived on land.

Some Uncommondescent commenters seem to be stuck on the idea that since these fins look like fins and not legs, the researchers should not claim that this provides "further evidence that ocean-dwelling mammals once lived on land". Let's examine this reasoning. Science has come to the conclusion that the ancestors of dolphins (and whales in general) were once land-dwelling tetrapods (i.e. they had four limbs). For these ancestors to evolve into dolphins, they must obviously have lost their legs somewhere along the way. This is not likely to have happened in one generation!!! More likely, the process would have been fairly gradual, starting with a four footed animal changing into a four-finned animal that subsequently lost it's rear fins - leaving us with the dolphins we see today. So, if today, a dolphin was found that sported extra rear limbs, we would hardly expect these to look like legs any more than we would expect it's front limbs to do. What we would expect, if descent with modification is true, is that these limbs would look like fins. The extra limbs found on this dolphin is thus consistent with the view that dolphins evolved from land-dwelling mammals.

JasonTheGreek asked at Uncommondescent: "Based on the fins, is there any way to show these were likely actual legs? Could these legs have held the weight of the body? ". The answer is no to both questions. When the pathway leading to the expression of these fins was last active, it was making fins, not legs. (Of, course, whether or not the extra pair of fins provide evidence that the ancestors of dolphins once lived on land depends on if they are due to an evolutionary remnant being switched back on - something that is by no means certain).

So, this find is consistent with dolphins have land-dwelling ancestors. However, like any singular piece of evidence, it is not a nail-in-the-coffin either for or against the theory. It is just a piece of evidence added to an already large pile of evidence that supports evolutionary theory.


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