Herding Ancient Domesticates: from Bones to Genomes
y| Victoria Mullin, Natural History Museum - May 2019 | Recent Lecture |
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We are all unique. We all have DNA, contained in all of our 37.2 trillion cells. There are two sorts of DNA. Mitochondrial DNA, located outside of the cell nucleus and inherited through the maternal line, gives energy to the cell. This is where the study of aDNA (ancient DNA) started, but technology has improved and now we are aiming at nuclear DNA (the famous double helix): it gives us more information – we can look at both parents. Your genome is split up into the letters ACGT (partly genes, governing hair colour etc) and consists of more than 3 billion base pairs. Because of how DNA is inherited our genome is a patchwork of the past. We differ from each other because of biomutation. Patterns cluster in populations. Cluster differences and similarities can place you in different populations. aDNA is obtained from ancient human archaeological material, plus animal remains including palaeo material, e.g. woolly mammoths. The first aDNA sequence was obtained from a sample from an extinct (but preserved) Quagga from the 1800s. The oldest aDNA obtained so far is 700,000 years old, from the permafrost. But the majority is from the last 7,000 years – since the last glaciation. DNA does degrade over time - so material millions of years old is (at present) outside of our grasp. There can be quite a lot of material, e.g. bone, teeth, but a bone in the inner ear (the petrous bone) is the most useful as it is the best part of the body for preserving DNA – obtained in this way from Ötzy. They also sampled his clothes to see what they were made from: bear, sheep and goat. Some environments are good for DNA as it doesn’t degrade so much – e.g. caves, which have a constant temperature - temperature fluctuations degrade DNA; deserts and tropics are bad. So, a “good” area is needed, especially if there are really low concentrations of DNA – it is easily contaminated, so the specialists extracting the DNA wear special suits. In as sterile an environment as possible, you get good DNA: drill bone, get DNA out, put it through processes, analyse what comes out. Endogenous DNA is what is wanted; they don’t want exogenous DNA: this is modern contamination. These techniques are bringing more and more information from the past to light. For instance, more studies will now be possible of Denisovans: previously, they only had part of a finger bone, from Denisova Cave, but they now have a jaw, from the Himalayas. And we now know that polar bears and brown bears could once interbreed. We have the aurochs genome, plus the woolly mammoth.
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aDNA and domestication: what is domestication? That humans have genetically adapted animals and plants to serve us? Was it a lengthy process? Domestication has happened with many different species. The dog: probably before 15,000 years ago. In the Near East there is the most genetic variation in animals, so it is where domestication likely occurred. Cows, pigs, goats: probably by 10,000 years ago. The domestication of goats was probably several different events - Iranian and Anatolian goats were probably domesticated at different times. Chickens, ducks, turkeys: more recently, the hamster: 20th century. A domesticated pig is smaller than a boar. The same processes for plants. Victoria is interested in what happened during Neolithicisation. Domestication was an important component of it, probably in the Fertile Crescent 11-9,000 years ago. Sometimes it was a “commensal” pathway: the dog (that is, the wolf) probably domesticated itself, by coming close to humans (for food). Then humans used this to their own benefit. So in a way, dogs domesticated humans! The geographical and temporal origin of dogs is disputed, perhaps from 15,000 years ago in Europe, 12,000 in Asia? The 4,800 year old, New Grange, male, dog was one of the earliest samples she has worked on. How inbred was it? It was compared with other breeds and found to be very similar to the modern local village dogs. It could probably digest starch (e.g. cereals) better than wolves – dogs were being given human scraps. It was between modern-day dogs and wolves. aDNA suggests a split between West and East Eurasian dogs: so, two domestications? 14-6,000 years ago? Were domesticated European dogs wiped out by an invasion of Asian dogs? “Domestication syndrome”: causing differences in the body. This is what dogs now have: they have become infantile, act like puppies - very different from wolves. Cows, sheep, goats, deer: these were our prey during the hunter-gatherer period, during which time we perhaps modified the landscape to be able to herd these animals – people already lived with livestock even during the hunting period. So the animals became habituated to human contact. People captured wild animals to try and breed them. So commensal or prey? We have to be able to tell if an animal specimen is wild or not.
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Work on the aDNA of cattle across Europe and Asia shows a complex picture. Cattle were first domesticated in the Near East (Taurean) 10,000 years ago, in Pakistan 8,000 years ago. Cattle look different in different parts of the world, e.g. in India, (Indicine) with the hump – from different wild bulls, but both descended from Bos primigenius: Aurochs, the original wild cattle (now extinct since the 1600s). Early Balkan domesticated cattle, perhaps, came direct from the Fertile Crescent. Later there is evidence that female domesticates were bred again with wild bulls to improve livestock. Also, Indicine cattle from the East – better adapted to drought conditions - may have been brought in during different wild bulls, but both descended from Bos primigenius: Aurochs, the original wild cattle (now extinct since the 1600s). Early Balkan domesticated cattle, perhaps, came direct from the Fertile Crescent. Later there is evidence that female domesticates were bred again with wild bulls to improve livestock. Also, Indicine cattle from the East – better adapted to drought conditions - may have been brought in during
the Bronze Age to improve stock during increased drought 4,200 years ago. That this process was quick is evident in the Levant – perhaps Zebu bulls (the Indicine introgression) were brought in, causing a 70% genome change. But the mitochondria are Taurean. Modern breeds show extreme domestication: dairy cattle are very inbred. We have also moved animals across the globe, which gives a false picture. So aDNA can give a snapshot further back in time.
At the Ness of Brodgar, perhaps a ceremonial site – a hub? - with temples: when it was abandoned c. 4,200 years ago, there was massive slaughter of cattle (to the Gods?), a large number for an island - were they bringing them in from elsewhere? But isotopic analysis suggests they were indeed local to the Orkneys, and related – so from a herd. So, they did have large herds of cattle on these islands. At Clad Allan in the Hebrides, all female cattle were inbred. So a local herd from the island - for dairy? This work helps archaeologists with regard to human lifestyle there. In the Russian silver foxes project: evidence of some genome change, also morphological changes: body shape, coat colour, as well as behavioural changes. Yvonne Masson |