Monday, November 06, 2006


Japanese fishermen have captured a dolphin with a pair of hind flippers.

I love stuff like this. Some cetaceans (whales and dolphins) have vestigial hip bones and some occasionally have malformed protuberances where the hind limbs once were, but this example has a full-blown case.

The flippers are about the size of a man's palm.

I hesitate to link to the Associated Press story (here at Fox News) because the reporting is so bad from a biological standpoint, but it's what I can find online.

What's wonderful about this find is not that these hind flippers show up right where hind limbs might have been predicted to reappear - and, I assume, contain the proper homologous bones. No, the wonder here is the theory of the hopeful monster. For those too lazy to click this link to Wikipedia, I'll explain briefly.

Hopeful monsters are the engine of macroevolution. Mutations create instances of gross morphological change in organisms. Because these organisms are radically different than the normal form, they are monsters. The "hopeful" applies to the possibility that these gross changes will prove a benefit.

While most modern evolutionary theory remains based in the standard theory of very small mutations that accumulate over time, the appearance of these flippers seems to show that hopeful monsters exist.

Almost certainly, a four-flippered dolphin would be less equipped than a two-flippered dolphin. The flippers are not used for propulsion, so an extra set would lead to drag without much benefit. Still, consider this a stepping stone for an interesting thought experiment. What if a dolphin with four flippers learned to be a shallow-water ambush predator? Four flippers might provide a more stable base on which to rest and leap from the seabed. If so, the presence of hind flippers would make the animal better equipped, and its similarly equipped offspring would outcompete its two-flippered conspecifics.

Given enough time, these creatures might evolve into an animal that could forage on land for short trips. Mutations that strengthen the four flippers and make them sturdier might stick if that proved an efficient strategy. Before you know it, we might have land-dolphins terrorizing the small fauna.

What's that? Something like this happened already?

Oh, I guess that renders my thought experiment moot. Or not.


Blogger Alex Epstein said...

What did they do with the poor dolphin?

November 13, 2006 10:50 AM  

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