OFFICIAL31 Why does the student say this:

[00:00.00]Narrator: Listen to part of a lecture in an anthropology class.
[00:06.75]Professor: So now that we've discussed how people in ancient societies tamed animals like cows and chickens for food and other uses. [00:14.99]I’d like to talk about an ancient culture that domesticated horses. [00:19.07]It's the Botai people.
[00:20.66]The Botai culture thrived over 5,000 years ago in central Asia, in what is now northern Kazakhstan. [00:29.02]Pretty much all of what we know about the Botai comes from three archaeological sites.[00:34.05]And we learned that the Botai were able to build large perennial villages, sometimes with hundreds of homes.[00:40.58]We also found horse bones at these sites and these can be traced back to the time of the Botai settlements.
[00:47.60]The climate that the Botai culture lived in…it was harsh. [00:52.69]And the Botai people…they didn’t really seem to have much in the way of agriculture going on.[00:58.39] So their whole economy was really based on horses. [01:03.12]And because horses can withstand the tough climate, they can survive ice storms and they don't need heated barns, the Botai people could settle in one place and rely on the horses for food, clothing and transportation.
[01:16.52]Student: So the Botai were the first to domesticate horses?
[01:21.65]Professor: Well, we are pretty sure that horses were first domesticated a bit earlier, to the northwest, in the area that is now Ukraine and western Russia. [01:30.61]It’s quite possible that some of those people later migrated east to Kazakhstan.
[01:35.68]Student: But what exactly tells us that these Botai people, that the horses in their area were really domesticated?
[01:43.94]Professor: As with most ancient history, there is not much that we can be certain about. [01:48.16]But we know there was a significant population of wild horses in that area. [01:52.79]So there were plenty of opportunities for the Botai people to find horses to domesticate. [01:57.77]We also know that horse milk was an important source of food for the Botai people. [02:03.17]What? Milking a wild horse? [02:06.27]Well, now, that would be impossible…to milk a wild horse. [02:10.07]And then… there’s the…Oh. Yes? Eric.
[02:13.34]Student: So you said last week that for some animals, like for dogs, there were physical changes taking place over the course of generations of dogs because of domestication. [02:24.19]So can we tell from those horse bones if it was sort of the same for horses?
[02:29.02]Professor: Actually, it wasn't. [02:31.26]We know that horses have not changed a lot physically as a result of domestication.[02:36.60]So those ancient horse bones don’t tell us much about domestication. [02:41.70]But…we've found that…um…we've found what maybe pens or corrals in the Botai settlements. [02:48.58]And not too long ago, a new approach was used to find out if the Botai people were keeping horses.[02:55.50] Soil samples from these pens or corrals show ten times the concentration of phosphorus.
[03:02.16]Student: Um…phosphorus?
[03:05.55]Professor: Yes. Phosphorus is a very significant indicator that horses, large numbers of horses were being kept in the settlements. [03:13.65]You see, horse manure, horse waste is rich in phosphorus and also nitrogen compared to normal soil.[03:21.98] But nitrogen is an unstable element.[03:25.16]It can be washed out when it rains or it can be released to the atmosphere, whereas phosphorus combines with calcium and iron, and can be preserved in the soil for thousands of years.
[03:36.99]The soil from the Botai settlement sites was found to have high concentrations of phosphorus and low nitrogen concentrations, which is important since it suggests that what we’ve got is really old, not something added to the soil more recently.
[03:54.38]Student: ) Wait. So if horses have been there recently, there'd still be lots of nitrogen in the soil.
[04:00.71]Professor: That’s right. Yes. Karen.
[04:02.83]Student: I just read an article. [04:05.39]It said that one way to determine if there was an ancient fireplace at an archaeological site was to check the soil for phosphorus. [04:12.55]So couldn't the phosphorus at the Botai sites just be from the frequent use of fireplaces?
[04:18.09]Professor: You are absolutely right. [04:19.77]However, when a fireplace leaves behind a lot of phosphorus in the soil, we'd also find an unusually high concentration of potassium.[04:30.26]But the soil at the Botai settlements, it was found with relatively little potassium, which makes it far more likely that the phosphorus came from horses. OK?
[04:40.38]Now, later on, people of the same region, northern Kazakhstan, started raising sheep and cattle.[04:48.15] And that led to a more nomadic culture. [04:51.64]Since sheep and cattle can’t survive harsh climates, they needed to be taken south every winter. [04:57.56]Moving around meant working harder but the trade-off was far richer, fattier milk year round and warm clothing from the sheep.