Since this article came out in The American Scientist (the only pop-sci magazine that IMHO has not gone downhill in quality over the past decade) in early 1999 (you can read the entire thing here (pdf)) I have read it many times, I used it in teaching, I discussed it in Journal Clubs, and it is a never-ending fascination for me. Now Andrew and Greg point out there is YouTube video about the fox domestication project:
Back in the 1950s, Dmitri Konstantinovich Belyaev started an experiment in which he selectively bred Silver Foxes, very carefully, ONLY for their tameness (and "tameness" was defined very rigorously in terms of type and speed of response, distance that triggers aggression, etc.).
What happened really fast in this experiment is that many other traits showed up, seemingly out of nowhere, in the subsequent generations. They started having splotched and piebald coloration of their coats, floppy ears, white tips of their tails and paws. Their body proportions changed. They started barking. They improved on their performance in cognitive experiments. They started breeding earlier in spring, and many of them started breeding twice a year.
Most of the people reacting to this experiment invoked pleiotropy, i.e., how changes in one gene affect expression of many other genes. See this NYT article for instance. However, even while I was reading it for the first time, my mind screamed - development! And not just development, but more specifically, heterochrony - change in timing of developmental event.
If you alter the expression of one of the genes that affects developmental timing, you affect all sorts of things.
For instance, when the neural crest cells migrate they become melanocytes in the skin - if due to changes in timing they are late to arrive to some distal parts, e.g., paws and tail-tips, those part will be white. Neural crest cells also migrate to become the adrenal medulla - that little part of the body that releases (nor)epinephrine (adrenaline). If fewer of those cells arrive there on time, less the animal will show stress-response later in life.
There appears to be tight correlation between timers that act on different scales, e.g., developmental and circadian timing, circadian and fast behavioral timing, circadian and seasonal timing, etc.
I always wished I could get a lab, some foxes, an IACUC approval and some money to run these animals through a battery of standard experiments comparing dogs, wild foxes and domesticated foxes on all sorts of parameters of circadian rhythms, photoperiodism (they did change their seasonality patterns of breeding, after all), etc.
The bottom line is that a subtle change in timing of expression of a single developmental gene, something one can select for by choosing one of the traits (in this case a behavioral trait), will affect the change in timing of expression in many other genes. The difference between wild and domesticated foxes may not be in any DNA sequence at all - it could presumably be all epigenetic (see also). Sequence differences would arise later, as the two populations are not inter-mixing any more (for 60 years now).
When you put together development, genetics and evolution, you can see that big changes (or, really, any changes at the very beginning of the evolutionary change) in DNA sequence are not necessary for big changes in entire suites of phenotypic traits. But in the 1950s, the bean-bag deterministic genetics was the norm, so the Belyaev experiment was a big jolt to the scientific community in the West (not so much for the Russian evolutionary biologists, though), so we need to look at this experiment through a decent grasp of history.
Now, I'd like to know what is the state of the experiment today. Ten years ago, the project appeared doomed - they had to sell foxes for fur in order to keep going at a small scale. Has this been fixed? Has anyone from the West help finance the continuation of the project? Has anyone in the West acquired some of the foxes and continued with the project? What are the recent developments?
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I seem to remember a comment that if a canine species or subspecies, like the dingo, has white tips to its tails, then it's been domesticated at some time. But I didn't understand why. Now I sort of understand.
As far as I know the project is still neglected and still struggling along with a fraction of the old number.
That's a fascinating story. I'd never heard about it until now.
If these foxes were bred for just tameness for another hundred years wouldn't their development stop? You can only get so tame and so these physical changes would also stop.
Once you get to the maximum in changes in timing, you can still keep selecting, but that would then involve sequence changes and will be a much slower process. Also, the traits may become dissociated from each other.
If these foxes are that tame, there's probably a market for pet foxes in America. That way you get fur without the guilt. That would keep the project going.
I wonder if zoos' breeding programs are inadvertently selecting for similar traits - if not "tamable", at least "thrives in captivity". Zoos haven't functioned as species arks for many decades - is that long enough to see this type of change?
"The American Scientist (the only pop-sci magazine that IMHO has not gone downhill in quality over the past decade)"
I agree. I first noticed the decline with Discover in the early 90s. I see a lot of pop sci mags on German newsracks. Wish they were available in English.