Posted on

Sneak Peak: Appendix on Domestication

One reason I’m an incredibly slow writer is I keep side-tracking myself. So here’s a brief look at the intro to the appendix on the domestication of sheep for my sheep book! The final version has footnotes. And a bibliography. Because I can’t stay on track to save my life, and there’s a lot of good sheep science out there, that’s why.

The origin stories of heritage breeds are rife with legend; for example here in the United States nearly every single one originating in the southeast is blamed on either wrecked Spanish galleons or early Spanish explorers turning them loose. This includes species for which such an origin might be vaguely plausible (ponies, goats), and those for which it emphatically is not (sheep with wool coats that require shearing). Humans love a stabilized breed of livestock, and they like to plant the origin of that breed as far in the past as they can reach. In Europe, a country’s indigenous breeds are often claimed to be remnants of the prehistoric past, preserved through the ages. In fact, that’s the story for Soay sheep, bolstered by their small stature, short tails, primitive appearance, and short coats of wool that naturally shed each summer.

Advances in genetic science in the past couple decades have taken a toll on the origin stories of heritage breeds, but in the case of the Soay have only confirmed that the breed’s history dates back to the dawn of domestication. How we can tell is a fascinating story of mitochondrial DNA (mtDNA) and a family of retroviruses that encodes itself into sheep DNA when it finds a host. It turns out that the majority of sheep breeds, even those billed as ancient indigenous breeds preserved forever in Europe, are the result of the second and later waves of sheep migration to come out of the Near East, and that selective breeding for secondary characteristics such as a coat of long white non-shedding wool occurred in the same place the sheep was originally domesticated rather than in Europe as some had previously theorized. In fact the only remnant remaining in Europe of that first wave of domesticated sheep is the Soay, left to fend for itself on the outermost island in the outer Hebrides for 5,000 years.

The story of how humans became shepherds starts around ten thousand years ago (10KYA). The version you’ll learn in school is that it happened in the same area where the domestication of cereal crops like wheat and barley did. School lied to you. Sheep were domesticated in the Zagros mountains of Iran and Iraq, and in the Anatolian mountains of Turkey. Yes, and. For much of the 20th century we thought domestication was a one time event. Then we began to suspect that it happened multiple times, but couldn’t actually prove it. Finally, after the discovery of DNA and after we’d learned to sequence it, and after we’d learned about mitochondrial DNA and how it’s passed down from mother to child and some areas on it mutate at very regular rates, we’ve come as close as we’ll ever be to proving that sheep are the result of what scientists like to call “multiple domestication events.” The original paper in 1995 identified one mitochrondrial DNA lineage, B, common among European breeds of sheep. In 1996 a follow-up identified mtDNA lineage A. Ten years after that first paper, in 2005, lineage C was identified among sheep in Turkey. Then in 2006 scientists identified lineages D and E from samples taken in Syria, Turkey, and Israel. Each of these probably represents a separate domestication event, meaning that at five separate times in five geographically separate places, human beings managed to take wild animals and turn them into domestic ones. We can know that they represent different domestication events because of the dispersion behavior of the ancestral mouflon: ewes stay with their mothers, and rams move on. Thus as time goes by any given herd will be dominated by the mtDNA of the most successful ewe or ewes, with genetic diversity supplied by a cast of wandering rams who contend for the attention of those ewes.

Those first domesticated sheep didn’t look a great deal like what people today think of as a sheep. When you read that word, you probably think of an animal that is largely white, perhaps with a black face and legs. The first sheep, though, looked like Soay sheep. They were small, they came in various shades of brown, and their wool was 2-3” long. Both males and females had horns. In contrast, modern sheep are generally mostly white, have wool that is 4” long or more, and may or may not have horns. Two very large differences in the way they look are tail length and shedding – the original domesticated sheep had short tails like goats, and shed their wool out every summer like dogs and cats do. More developed sheep breeds have long tails that hang past their hocks, and with a few exceptions their wool does not shed so they must be sheared. Another very large (literally) difference is their size. The ancestral mouflon and the ancestral primitive sheep were small animals, with the ewes weighing at most 50 pounds. The push for increased size in domesticated livestock didn’t really take hold until the 16th and 17th centuries in Europe, yielding the large white fluffy sheep that most people think of as the canonical sheep.

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.