A very interesting article at Scientific American details a multi-year experiment conducted in Russia which gives insight into how early humans domesticated dogs:
Belyaev and other Soviet-era biologists looked around at domesticated dogs, a species they knew had descended from wolves, and were puzzled. They could not figure out what mechanism could account for the differences in anatomy, physiology, and behavior... Belyaev hypothesized that the anatomical and physiological changes seen in domesticated animals could have been the result of selection on the basis of behavioral traits. More specifically, he believed that tameness was the critical factor...And as a bonus, this interesting tidbit:
Starting at one month of age, and continuing every month throughout infancy, the foxes were tested for their reactions to an experimenter. The experimenter would attempt to pet and handle the fox while offering it food. In addition, the experimenters noted whether the foxes preferred to hang out with other foxes, or with humans.
Then, upon reaching sexual maturity (seven to eight months), they had their final test and assigned an overall tameness score. They rated each fox's tendency to approach an experimenter standing at the front of its home pen, as well as each fox's tendency to bite the experimenters when they tried to touch it. Only those foxes that were least fearful and least aggressive were chosen for breeding...
The result of this breeding program conducted over more than 40 generations of silver foxes was a group of friendly, domesticated foxes. These domesticated foxes, which were bred on the basis of a single selection criteria, displayed behavioral, physiological, and anatomical characteristics that were not found in the wild population, or were found in wild foxes but with much lower frequency...
The domesticated foxes were more eager to hang out with humans, whimpered to attract attention, and sniffed and licked their caretakers. They wagged their tails when they were happy or excited...
More than 50 years have passed since Belyaev began his silver fox breeding program, and research with these foxes continues to uncover the genetic changes that occur with consequences for physiology, anatomy, behavior, and cognition, as a result of the process of domestication, though on a smaller scale. In 1996, the breeding population contained 700 individuals, but by 1999, it was down to 100. Because of the realities of the Russian economy and the shortage of funding for science, in order to maintain the research, some foxes had to be sold for fur, and some are now being sold as pets...
Darwin noted, in On the Origin of Species, that “not a single domestic animal can be named which has not, in some country, drooping ears.” Drooping ears is a feature that does not ever occur in the wild, except for in elephants...Upright ears being presumably more suited for the hazardous life in the wild. Many of the domesticated foxes developed drooping ears.
Via Not Exactly Rocket Science.
I've actually read about this and I found the place where they sell those silver foxes online.
ReplyDeleteReally what's the site address?
DeleteThey have video of the fox farm plus a little background described in the post on this NOVA show: http://www.pbs.org/wgbh/nova/nature/dogs-decoded.html
ReplyDeleteThe aggressive-bred foxes are angry MFs.
I've never seen a horse with drooping ears. It may happen very rarely as a deformity, but it's not part of any breed that I know of. (Other equids like donkeys do have floppy-er ears, although not really folded over, perhaps that is what Darwin was thinking of.)
ReplyDeleteFascinating experiment with the foxes. It's interesting that they avoided contact to make sure they were breeding for genetics alone and not the ability to learn tameness. I wish they would have had another group where they did interact regularly, it'd be interesting to see what would develop from that and how it would be similar or different from the first group.
I recorded the Nova special as well. Absolutely fascinating.
ReplyDeleteThe article linked does not explain the connection between tameness and drooping ears, so I thought I'd chime in. The biological connection is quite clear, although perhaps a bit counter-intuitive.
ReplyDeleteThe main actors here are neural crest cells. They form early in embryonic development (around day 18 for humans) almost as a side product of the formation of the neural tube, which is the precursor of brain and spinal cord. Neural crest cells don't become part of the neural tube, but migrate across the body in predetermined paths and eventually differentiate into a variety of tissues: most of facial bones and cartilage (including outer ear), peripheral nervous system, all skin pigment cells (melanocytes), parts of the adrenal glands, etc. Adrenal glands produce stress hormones, such as adrenaline and glucocorticoids, and if this production were to be reduced, it would lower the stress and fear responses in the animal - that is, make it more tame.
For whatever reason, changes in master control of all development happen more readily than fine tuning of individual processes during artificial selection. So selection for tameness alone is likely to work through a global down-regulation of neural crest development. If migration and differentiation of neural crest cells is stopped in its tracks earlier than it should, or if it is delayed at the beginning, you end up with adrenal glands that are not fully developed (thus producing less stress hormones), reduced growth of facial bones and cartilage (leading to a short nose and floppy ears) and pigment cells that fail to reach some of their targets (leading to white spots on the forehead, belly and tips of limbs).
Interestingly, some differences between humans and other apes seem to parallel those between domesticated and wild animals, leading some scientists to suggest that a kind of "self-domestication" (selection for "tame" individuals who would contribute to the group, and ostracizing of those who were more selfish) may have taken part in human evolution.
Google should bring up more reading material about the neural crest and its role in domestication.
Interesting. Thank you, bucaneer. I hope you stay on at this blog as a regular reader.
DeleteSure - I'm doing a backward crawl through the archives now, and since I got this far, I think I'll stick around. Congratulations on a great blog!
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