The Domestication of Sheep

This is a mouflon, a type of mostly wild sheep that is a likely ancestor of all the domesticated sheep on earth today. Even if most of our clothing isn’t made of wool and most of our food isn’t lamb, human life wouldn’t be the same without this animal.

Sheep and goats were the first domesticated herd animals — starting about 11,000 years ago in the Middle East. First bred for meat and later for wool, domesticated sheep were very different from their wild neighbors.

The neolithic humans who captured and domesticated these animals radically changed their environment. These sheep no longer had to worry about carnivorous predators, and they also lived in much more crowded conditions. Humans killed off the older rams and ewes to propagate the lambs more quickly.

The domesticated sheep changed quickly, as the evolutionary record shows: sexual dimorphism (the physiological difference between males and females) decreased. The large horns of the more primative male mouflons illustrate — the horns were no longer needed to compete for females or ward off predators. The domesticated sheep become fertile earlier, and the females bear far more litters.

Extra interesting is what happened to their brain size — it decreased, like, a lot. Compared to sheep 10,000 years ago, modern sheeps’ brains are 24% smaller. The areas that particularly shrunk were the ones related to the limbic system, the “emotional” parts of the brain that respond to threats.
Overall, we bred sheep to be stupider and less emotionally reactive.

In other bad news for the domesticated sheep, they were subject to more disease because of crowding conditions — scientists have actually traced the lineage of sheep by looking at the retroviruses they have as genetic date markers. The mortality rates of newborn lambs skyrocketed in these conditions.

But humans found it more than worthwhile to deal with the diseases of domesticated sheep, and the work involved with taming and caring for them. 60% of all mammals alive now are ones humans domesticated, according to a 2018 report. Even though cows and pigs lead the way in those numbers today, sheep began this trend.