Where did domestic chickens come from?
Earlier studies on the modern chicken, Gallus domesticus, had claimed it originated some 10,000 years ago in China and South East Asia, with the earliest European chickens supposedly dating back 7000 years. Now, scientists around the world have been collaborating to put this claim to the test, and have found that certain samples had been inaccurately dated by thousands of years, meaning chickens are actually much younger in evolutionary terms than we first thought. The two studies, published in the journals Antiquity, and The Proceedings of the National Academy of Sciences USA, were carried out by academics at a number of universities around the world including Cardiff, where Julia Best is based. She told James Tytko what they’ve found...
Julia - The methods that have been used prior to our studies to assign the age to these chickens have been indirect. That means they've been associated by the archaeological context in which the bones were found; things like types of pottery, coins, things that can give us an approximate date. One of the methods we used is radiocarbon dating, which is a direct form of dating; analysing the levels of unstable and radioactive carbon 14 present in the ancient chicken bones. That rate of radioactive decay gives us as archaeologists a ticking timer to measure.
James - And what sort of errors were you able to rectify with this much more accurate dating technique?
Julia B - One really good example comes from Bulgaria where a specimen was thought to be about 7,000 years old. But when we did radio carbon dating, it was actually revealed to be less than a hundred years old and it was a modern intrusion. Other ones were still ancient, but were much more recent than previously thought. For example, maybe being Roman and medieval in date, rather than much earlier such as bronze age or iron age.
James- That's incredible how far wrong that previous dating was to me. Can I move us on to think about what we know about when chickens were first being domesticated, what their evolutionary ancestors may have been and what instigated people taking them into their homes and communities?
Julia B - The theory we are putting forward at the moment is that it may have been to do with rice cultivation. As cereal crops start to be domesticated in this area, such as Thailand, what we are seeing is a really nice correlation between the date of this crop domestication and the date where we're first seeing chickens in the archaeological record. So, maybe the clearing of jungle areas for rice cultivation fields could have created an appropriate environment for the red jungle fowl, the chickens ancestor or primary ancestor, which could have then been attracted into the human niches based on the availability of food among other things.
James - And when we start to see chickens coming over to the West, firstly, when? And secondly, are they coming over the animal that we now view as a common source of food, whether for their eggs or for their meat, or were they coming over in a different capacity?
Julia B: - We now think that they did not arrive in Europe until the first millennium BC, probably about 800 BC. So, out of the 23 bones that we radio carbon dated, 18 of them were much more recent than had been claimed. So now that we can rule out those intrusive chickens, we can get a better understanding of what people were actually doing with them and how they were interacting. Let's take Britain as an example for now, when these animals first arrive chickens do not seem to be primarily considered as food. The earliest chickens that we have in Britain are buried alone in pits. They're whole animals, they're not butchered. And they seem to have lived quite a ripe old age. This indicates more that they have a special status. Maybe they're considered exotic. Maybe they are a status symbol and they might also have ritual religious connotations. It takes perhaps up to 500 years from a chicken's first appearance in an area for them to be more considered as a common food.
James - That's really amazing to me. They're first viewed as these interesting exotic animals. Do we have a sense of what changes the chicken has gone through since it was first domesticated? Because it strikes me that the modern chicken serves a lot of purposes for humans as they currently are, which may have not been so useful in the wild being such efficient layers of eggs, for example, or having such meaty flesh.
Julia B - Exactly. That is a really important change. Some of the early changes may have been to do with their outer aesthetic: what they look like. But some of the key changes you pick up on there are things like the ability to lay frequently. We know that it must be quite soon after chickens are domesticated that they have the capacity to lay regularly, but we don't know whether that was actually selected for until much later on. So maybe things like egg laying weren't the most important to begin with.
James - Chickens are obviously such a hugely culturally significant animals, it seems pretty much all across the world. That's maybe even more apparent now that they're becoming more expensive thanks to a variety of factors...
Julia B - Of course the more we learn about animals and where they came from, how they were domesticated, and how we've changed them, that can feed into things such as looking forward to sustainability. Things like avian diseases, thinking about how we interact with our food animals. And, of course, that's a really contemporary key theme: how we get our food, food miles, consideration of animal human relationships. So I think it provides a great lens to look at both modern society and ancient society.