Wednesday, August 01, 2018

Whale evolution

I was asked to comment on this:

For me personally (as a geneticist) comparative genomics (comparing DNA sequences between different species) has really sealed the deal on evolution. Even if Darwin had never lived and no one else had come up with the idea of common ancestry, modern genomics would have forced us to that conclusion even if there was no other evidence available (which of course manifestly isn’t the case). For example, we see the genes for air-based olfaction (smelling) in whales that no longer even have olfactory organs.

I'm not a Cetologist, but neither is Venema. Speaking as a laymen, a few observations:

i) Both old-earth and young-earth creationism make allowance for adaptation and loss of function. For instance, blind cave fish are consistent with creationism. 

ii) From what I've read, one of the challenges facing macroevolution isn't loss of information but the source of new information necessary to generate new organs and body plans. 

iii) I guess what Venema is angling at is that whales have vestigial genes for air-based olfaction because their distant ancestors were land animals. Put another way, the assumption seems to be that marine animals never had any need of air-based olfaction, since their natural element is water. But is that true?

Years ago I saw a nature show in which a killer whale was cruising the shoreline of an island breeding ground for penguins and seals. It doesn't take much imagination to see how air-based olfaction might be useful for a marine predator whose diet includes semiaquatic prey that spends on some time on the beach. Likewise, I saw a nature show in which polar bears hunt beluga whales that surface for air in breathing holes in sea ice. Once again, it doesn't take much imagination to see how air-based olfaction might be useful to sniff out polar bears. That might be too late in the case of breathing holes, but ice flows also have shifting stream-like openings, where it might be useful to sniff out prowling polar bears. And even if there's loss of function in extant species, it might have conferred a survival advantage in the past. 

iv) But even if that's an explanation for why beluga-like or orca-like whales once had air-based olfaction, why whales in general? To take a comparison, I have many organs and body parts, not because I'm human, but because I'm mammalian. By the same token, a dormant capacity for air-based olfaction might be part of the cetacean package, even if it's potential utility is confined to particular species or adaptations. 

v) Finally, here's an overview of the massive hurdles facing whale evolution: 


  1. Comparitive genomics presents a problem:

  2. I've read in a few places that the same gene can be found in multiple species but serving different functions (analogous to the same word-token having different meanings across contexts). There's no simple one-to-one correspondence between genes and functions. How does Venema know that those genes don't serve a different function in whales?