Maybe it's just because Fifi and Rex are always close to hand for ad hoc analysis, or maybe it's because cats have so obviously already hit the pinnacle of development and ceased to need any changes, but dogs have always been an example pointed to by both sides of the evolution debate. Evolution advocates point to them as an example of selective forces (with dog breeding, man-made selective forces) changing population characteristics. Evolution opponents have come from both sides: Some arguing that the fact dogs haven't split into separate species shows that speciation via selection is impossible, others arguing that the level of genetic diversity in dogs is too great to be the result of random mutations, and thus points to some other force at play. The poor dogs, meanwhile, are too stupid to pick up on any of this but happily offer their loyalty and frisbee fetching skills to all comers.
However, some recent genetic research sheds a bit of interesting light on the evolutionary history of dogs. Researches sequenced the mitochondrial DNA of several breeds of dog, plus modern grey wolves, to which dogs are believed to be closely related. Their results suggest that modern dogs were domesticated and removed from the wolf gene pool about 15,000 years ago, very recently by an evolutionary timescale. However, during that time dogs have built up and retained far more minor genetic defects than the wolf population -- and also much more genetic diversity (thus allowing all the different breeds of dog).
The researches believe the cause of this is that with human care, genetic changes which might have reduced a wolf's chances of survival are allowed to flourish among the dog population because they receive human care, and are thus under less pressure from natural selection. Thus, the modern genetic diversity among dogs is primarily the result of human care. I hardly think this is what the Discovery Institute had in mind, but we now seem to have found a population whose current genetic makeup is the result (in part) of intelligent design -- or at least of pampering.
UPDATE: Razib has some additional thoughts on dogs and human influenced evolution over at Gene Expression.
FROM THE ILLUSTRATED EDITION.
2 hours ago
11 comments:
1) i note on my weblog that fisher suggested this in genetical theory
2) i think 'deleterious' is contextual. dogs have been strongly selected in other areas that wolves have not, and yet we don't consider wolves to exhibit a lack of the ability to read human faces....
I knew I'd found the link via some other blog, but I have this bad habbit of opening interesting articles in another browser window and then leaving them open for a couple days before I get around to reading and writing about them.
Also a very good point about the new selective pressures that dogs face but wolves don't. Dogs don't have as hard a time just surviving, but we're much more likely to keep them around and let them reproduce if they don't make messes in the house, don't bite the children, etc., which after a few millenia has got to start having an strong selective effect, though not a 'natural' one.
I suppose it's similar, in a way, to the change in selection of humans that the advent of civilization has brought about. Although we're not likely to be eaten by a cave bear these days, there are certainly some traits that make one more likely to prosper in modern society than others. Though, of course, the definition of 'prosper' also has to be examined, since many of our most 'successful' members of society have scant interest in reproducing these days.
Though, of course, the definition of 'prosper' also has to be examined, since many of our most 'successful' members of society have scant interest in reproducing these days.
sure. success is contextual. but note that the correlation between low fecundity and high SES might be a feature of the last 100-200 years. in fact, in almost certainly is, otherwise as a species we wouldn't value high SES, since that reduces fitness :)
I think the evidence which you have presented is also an indication of another fact: as the genetic manipulation of dogs by modern humans has occurred only 15 or so thousand years ago, this is another indicium that modern humans have only been on the scene for the last ten to fifteen thousand years. Interesting.
Some would say that, absent human 'design,' feral dogs will tend to go back to the wolf, or something similar.
You may find
http://www.carolinadogs.com/ and http://www.carolinadogs.org/
interesting.
Some would say that, absent human 'design,' feral dogs will tend to go back to the wolf, or something similar.
You may find
it is an empirical fact. there tends to be a common convergence in regards to what 'feral' dogs look like the world over.
I suppose the really interesting thing would be if one of the breeds of dog that has gone a long way from the wolf set of characteristics, say a dachshund or a chihuahua, could find a completely new niche in the wild, which would result in selection divergent from the rest of the dog gene pool.
Darwin--
You mean dachshunds living in burrows like mustelids, maybe? Well, that would be the whole selection idea. Actually, though, as with the Carolina dog pariahs tend to adapt to their immediate environment. Hence the predominance of shorthaired yellow dogs in southern coastal pinewoods rather than shaggy gray wolfish dogs. I'm told there was a variety of feral dog on the Galapagos that survived by hunting iguanas on lava flats. Old photos show it had enormous ears (heat dispersal) and it is hypothesized that it also had extra-thick paw pads for walking on the hot lava. Unfortunately all were exterminated and I do not think specimens were saved.
Now that coyotes have spread across the continent, perhaps feral yellow dogs will be absorbed by that population. I've heard that coyotes are petty much doing in what was left of the Southern Red Wolf.
...or maybe it's because cats have so obviously already hit the pinnacle of development and ceased to need any changes
I completely understand what you were trying to say about the "pinnacle of development" (I leave for work most days thinking how nice to would be my cat...). But, I just wanted to point out that organisms don't evolve b/c they "need" changes. Artifical selection can do that, working with natural/induced variations...but good old natural selection just happens. After all, giraffes didn't "need" longer necks to eat the leaves higher up and just evolve them b/c of that need. Instead, giraffes with randomly longer necks were conveniently able to eat more leaves, have more baby giraffes with longer necks, etc. Just a technicality...
NewDad,
Indeed, you caught me professing my strong preference for cats rather than a correct description of selection.
For whatever reason, the idea that a stable population is one that is being selected for stasis seems to be one that people have difficulty with. I seem to recall this being one of the hardest concepts for a lot of the students in my college Anthropology class, in that most students had the idea that either species must always be directionally evolving, or else that they must "decide to evolve" at certain junctures.
I think a lot of people still have a 19th century idea of 'progress' confused with evolution, in which it is assumed that species all 'want to get better'.
species must always be directionally evolving, or else that they must "decide to evolve" at certain junctures.
The first statement sounds kinda like the Red Queen Hypothesis to me, except maybe for that 'directionally!' As for the second, yeah, it's surprising people assume some sort of conscious intent on the part of the individual, but that's not a new idea. I've been reading Teilhard de Chardin's The Future of Man on and off over the past few months and his progressivist tendencies really do stand out. The 'everybody's trying to get to where we are' snobbery must have been really entrenched in the thinking.
I hope 'newdad24' didn't think I was suggesting conscious choice or Lamarkianism on the part of the dogs. Dogs do have a pretty flexible genome, and their environment seems to be able to force their adaptation as easily as does human selective pressure. So although there's a general type, certain traits (say, ear size) may differ in some places from that in others.
BTW, my bad about the red wolves--I skipped over to some articles from the Smokey Mtns reintroduction program yesterday after visiting here, and it seems that they can't make up their minds whether red wolves & coyotes are one species or two. Apparently they're genetically indistinguishable.
The possibility that they are descended from coyote/gray wolf hybrids was also mentioned.
Adaptation strikes again? Stay tuned...
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