Rat races

3 minute read

Read Nick Wade's article about Siberian rat breeding experiments. Two strains of rat: one tame and one aggressive. Now they're screening their genomes to see what's up.

"The ferocious rats cannot be handled," Mr. Albert said. "They will not tolerate it. They go totally crazy if you try to pick them up."
When the aggressive rats have to be moved, Mr. Albert places two cages side by side with the doors open and lets the rats change cages by themselves. He is taking care that they do not escape to the sewers of Leipzig, he said.

Well, those might be some nasty rats, but odds are they wouldn't do too well in a natural sewer. Their Siberian rat cages protect them just as much as their tame relatives; their alleles probably are already present in the wild population, and the pattern of selection on them almost certainly wouldn't change just because of their release.

(I know what you're thinking. The rats from NiMH were entirely different! They had some kind of special pharmaceutical alteration.)

The article covers Belyaev's experiments, which are best known for the tame foxes:

The experiment did not become widely known outside Russia until 1999, when Dr. Trut published an article in American Scientist. She reported that after 40 years of the experiment, and the breeding of 45,000 foxes, a group of animals had emerged that were as tame and as eager to please as a dog.
As Belyaev had predicted, other changes appeared along with the tameness, even though they had not been selected for. The tame silver foxes had begun to show white patches on their fur, floppy ears, rolled tails and smaller skulls.

Sure, the founding of the breeding population would have gotten a few rare alleles by chance, but we're really talking about the selection of alleles that are mostly already fairly common in wild foxes (common enough to get into a small sample of them, anyway). So this breeding experiment has concentrated a few alleles that are generally present into a single group where they are always coexpressed.

Anyway, nobody ever seems to talk about the other colony of "vicious" foxes. The article covers a few surprising correlates of tameness, like the ability to follow gaze. But what are the surprising correlates of aggressiveness? Are these foxes and rats sociopaths?

The root question is whether humans domesticated themselves, and therefore have some of the same genetic changes as these domesticated rats and foxes. But then, the rats and foxes haven't so much undergone genetic changes as simple enrichment of alleles that are already common. Which means that they may have unusual phenotypes as a result of these alleles being coincident at high frequencies, but those alleles already are doing something in normal, wild (and mostly solitary) animals. This doesn't mean that the tame phenotype should already exist -- even if all these alleles are independently common, if there are enough of them they may never all be present in any single wild individual.

So the interesting question is why these alleles that permit domestication in combination should already be common. Do they all contribute to variant behavioral strategies -- such as a proper balance of fear, aggression, tolerance, and sociality? Are they all in selective balance? They aren't all present because they make animals tame, at least, not if tame animals are naturally rare. But each has some advantage on the wild genetic background, or they wouldn't persist as common functional variants.

And if these genes did change in identifiable ways during human evolution, well then, what started the process? It is easy to imagine sociality evolving in parallel in humans and domesticated animals -- at least in certain respects -- but widespread changes in systems that are often found in selective balances would be sort of surprising. With domesticated animals there is a huge fitness cost to aggression. Is that really true of people?

It's a great topic, and a great story. Considering how much money there is in beef, it seems like it would be a small investment to raise 40,000 bison, or pronghorn, or eland, or any number of other wild animals to select for tameness. Maybe Ted Turner could do it.