Posted by jlwile on February 16, 2012
I recently read about a fascinating experiment that has been going on in Russia for the past 50 years. Dmitry K. Belyaev acquired some silver foxes from a farm that breeds them for their fur. The farm started about 50 years prior to the experiment, so several generations of foxes had experienced human contact to some degree. However, the foxes still did not care for human contact and were quite aggressive if they were forced into such contact.
Belyaev took this group of foxes and began trying to develop a new trait: tameness. Each fox was exposed to a human for a specific amount of time at specific ages. The fox was then evaluated based on how well it reacted to the human, and only the foxes with the best overall reactions to humans were bred. In a mere six generations, some foxes were born that not only enjoyed human contact, they actually craved it! This behavior became characteristic of the entire population, so that the foxes now behave like dogs – wagging their tails, whimpering, licking people, and generally doing all they can to interact with people.1
Now these results are cool on at least two levels. First, I was shocked at how quickly the foxes adapted to human socialization. For human-friendly foxes to appear in a mere six generations just astounds me. I know that dogs were domesticated from wolves, but I always imagined that it took a long, long time. After all, a lot has to change in order to take an animal that avoids people and is aggressive towards them and turn it into an animal that not only jumps up on your lap to cuddle with you but begs to be able to do so! According to this experiment, however, the change can happen quickly. Second, I just think it would be incredibly cool to have a pet fox. From time to time, I see a wild red fox in the neighborhood where I live. I would love to have such a beautiful animal as a pet!
Those are the cool aspects of the experiment. However, there are a lot more interesting aspects to the experiment, and they indicate that we still have a lot to learn when it comes to genetics.
You see, while the experimenters selected for one trait and one trait only (tameness), the new population of silver foxes is different from the original population in many other aspects, and it is not clear how those aspects necessarily relate to tameness. In order to make this experiment a bit easier to discuss, I want to define two terms for you. Genotype refers to the genetic makeup of a given organism. Phenotype, on the other hand, refers to the observable characteristics of a given organism. For example, before I started going gray, I had dark brown hair. That’s my phenotype. The reason I have dark brown hair is because of specific genes that I have. If I listed all the genes that make my hair dark brown, that would be the genotype that leads to my phenotype of (formerly) dark brown hair.
In the case of this experiment, the only phenotype that was selected for was tameness. It turns out that in a subsequent paper, the scientists involved in the experiment located two sections of the fox DNA that seems to have changed remarkably from the original population.2 While the specific genes involved in this change have not been identified, when they are identified and characterized, we will have the genotype that is associated with the phenotype of tameness.
Here’s the interesting part: While the only phenotype being selected for is that of tameness, other phenotypes have arisen that are quite different from the original population. To me, the most interesting one had to do with reproduction. Wild silver foxes mate early in the year, in response to increasing daylight hours. They do not breed at any other time of the year. Silver fox farmers have long tried to change this so that they can produce more foxes, but they have never been successful. In this experiment, however, many of the foxes now breed at different times of the year, and some have even mated twice in the same year. By selecting just for tameness, somehow the experimenters have been able to produce a reproductive change that silver fox farmers have been trying to make for many years!
Other changes have been seen as well. Certain hormone levels are significantly different from the original population, and the pups reach sexual maturity about one month earlier (on average) than the original population. In addition, they have (on average) one more pup per litter. Once again, these are phenotypes that would be very valuable to fox farmers, but they were not produced by selecting for such phenotypes. Instead, they were produced by selecting only for tameness.
Another mysterious phenotype that has become more frequent is a specific pattern of white spots on the head that is referred to as “Star spotting.” The spotting pattern appears in farm-raised foxes, but at a very low rate (about 71 in every 10,000 foxes). In the current population of tame-bred foxes, the pattern shows up in just over 12% of the population. Once again, then, by selecting only on the phenotype of tameness, the experimenters have increased the frequency of a seemingly unrelated phenotype by more than a factor of 17! There were other phenotype changes as well, but I think you get the idea.
So what does all this mean? To one extent, it just confirms what we already know. Very few genes affect only one trait. Instead, most genes affect a variety of traits. We call this pleiotropy, and it means that when you make even a small change to the genotype of an organism, you will probably see lots of changes in the organism’s phenotype. However, there has always been a thought that the phenotypes which are affected by a specific genotype are at least partially related to one another. This experiment shows that’s probably not the case. While hormone levels would be expected to change as a result of selecting the tamest foxes, you would not necessarily expect breeding patterns, fertility, and coat coloring to change. Nevertheless, they all did. That tells us we still have a lot to learn about how the DNA of an organism relates to the various characteristics that organism possesses.
It also tells us that these changes can occur rather rapidly. Look at the picture that appears on top of this post again. It took only a few generations to make that change in some members of a population, and it took only 50 years to make the change throughout the entire population. That tells us populations can change rapidly, given the right kinds of selection. This is precisely what young-earth creationists believe. In order for the animals on the ark to diversify and produce the variety we see today in the various kinds of animals God created, populations must be able to change rapidly, given the right kinds of natural selection. This experiment using artificial selection provides evidence the young-earth creationist view is correct on that point.
1. Trut L, Oskina I, and Kharlamova A, “Animal evolution during domestication: the domesticated fox as a model,” Bioessays 31(3):349-60, 2009.
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2. Kukekova AV, et. al., “Mapping Loci for fox domestication: deconstruction/reconstruction of a behavioral phenotype,” Behavioral Genetics 41(4):593-606, 2011.
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