How to conquer the world

Our species Homo sapiens has been around for some 200 000 years, and is generally thought to have evolved from older human species present in eastern and sub-Saharan Africa (University of Utah, 2005). But how did we come to be global (and even lunar) mammals? Debate still rages over how long ago H. sapiens left Africa, with some people arguing as late as 50 000 years ago and others as early as 200 000 years ago.
There is matching controversy about how we spread out of Africa: was there only one African exodus, or many spread over a longer time period? Did all or only one of them make it past the Near East? Did we completely replace older Homo species who already lived across Eurasia, or did we interbreed with them? If we did interbreed, was it complete free love that hippies would have been proud of, or did it only happen occasionally? (Reyes-Centeno et al., 2014). These questions may be a bit closer to being solved thanks to some recently unearthed fossils (fig. 1).

Figure 1. Some of the latest finds from Chinese caves. A & B, front and side views of the mandible fragment from Zhirendong. E & F, front and side views of the two molars from Zhirendong. G, assorted teeth from Lunadong. (Bae et al., 2014; Liu et al., 2010)
Figure 1. Some of the latest finds from Chinese caves. A & B, front and side views of the mandible fragment from Zhirendong. E & F, front and side views of the two molars from Zhirendong. G, assorted teeth from Lunadong. (Bae et al., 2014; Liu et al., 2010)

In 2007, two molar teeth and a large fragment of a lower jaw (mandible) were discovered in a cave called Zhirendong in south China beneath layers of rock that had been reliably dated to at least 100 000 years old (fig. 1 a-f) (Liu et al., 2010). This wouldn’t be that surprising as archaic species of Homo are known to have been present in the region long before then, except for the size and shape of the teeth and mandible.
The teeth were smaller than the investigators expected, falling right in the middle of the range of sub-Saharan teeth of the same age. The mandible fragment also possessed a distinct chin (fig 2), a feature that was absent in all known archaic Homo species, variably present in early H. sapiens and is seen in all modern H. sapiens (i.e. us). So far all the signs point to a fully modern human in China over 100 000 years ago. However, the mandible didn’t look quite right. It was too heavily built, and certain contours and bony spines representing muscle attachments looked just like those of archaic Homo species.

Figure 2. B, lateral view of the mandible fragment. D, digital model of the right half of the fragment. Note how the rounded bottom left curve sticks out beyond the rest of the bone - this is the chin. (Liu et al., 2010)
Figure 2. B, lateral view of the mandible fragment. D, digital model of the right half of the fragment. Note how the rounded bottom left curve sticks out beyond the rest of the bone – this is the chin. (Liu et al., 2010)

Fast forward to 2014, and two more teeth (fig. 3) have been discovered in a  cave called Lunadong in Guagnxi Province, China (fun fact about my home town – YouTube. That’s not my accent though, promise), and are between 70 000 and 127 000 years old (Bae et al., 2014) . The team here used linear measurements to measure size and GMM to measure the shape of these teeth and compare them to a massive sample of fossil teeth, including modern humans from 10 000 to 200 000 years ago and  teeth from Neanderthals, H. erectus, H. habilis, australopithecines and paranthropines. Both teeth compared more favourably with teeth of modern humans than with teeth from any other hominin species investigated.

Figure 3. Different views of two teeth: top, upper left second molar; bottom, lower right second molar. Views are of the biting surface, view from the front, the back, from the cheek, from the tongue. (Bae et al., 2014).
Figure 3. Different views of two teeth: top, upper left second molar; bottom, lower right second molar. Views are of the biting surface, view from the front, the back, from the cheek, from the tongue. (Bae et al., 2014).

So we have what looks like pretty solid evidence of a modern human presence in the Far East around 100 000 years ago but we still don’t know how they got there. Enter a pan-European team based in France, Italy and Germany who carried out some sophisticated genetic analysis of 714 modern humans and paired it with GMM shape analysis comparing the skulls of 233 museum specimens of H. sapiens covering the last 6000 years (Reyes-Centeno et al., 2014).
They used genetic and cranial shape data to test four hypotheses of how we might have spread out of Africa (fig. Xx).

Figure 4. Possible routes out of Africa. EE, eastward expansion; BSD, beachcomber single dispersion; MD, multiple dispersals; MDI, multiple dispersals with isolation. (Reyes-Centeno et al., 2014).
Figure 4. Possible routes out of Africa. EE, eastward expansion; BSD, beachcomber single dispersion; MD, multiple dispersals; MDI, multiple dispersals with isolation of Australian populations. (Reyes-Centeno et al., 2014).

The conclusions they came to were clear. It seems as though modern Australian aborigines are descended from a population of H. sapiens that reached Australia 50 000 years ago, around the time that some people proposed we first left Africa. The same group of early modern humans also stopped off on the islands before the way Australia, giving rise to modern Melanesian and Papuan populations. Crucially, the genetic evidence suggests that modern Australian and South African populations were separated at around 116 000 years ago, which tallies well with the famous modern human skulls from Skhul at Qafzeh dating from between 90 000 and 120 000 years ago.
The team also noticed that Melanesians and Papuans differ slightly in their genetic make-up from modern Australian aborigines – evidence of multiple Out of Africa events which didn’t completely replace older populations, but only show signs of limited inter-breeding and did not reach Australia – the MDI model in figure 4, above.
This is also the conclusion that Liu et al. reached concerning the mandible fragment at the start of this post – some very modern-looking features, but with some archaic features thrown in for good measure.

So how do you conquer the world? Don’t make it obvious: have a few goes and spread them out over a period of about 80 000 years, preferably between 130 000 and 50 000 years ago. Make friends with the locals if you can – engage in a bit of free loving, it can only help you.

By the way, I’m sure there are far more fossils that are more widespread than those I’ve mentioned here, I just wanted to highlight the fact that China seems to be hot property at the moment for discovering hominin fossils – who knows what could turn up in future!

As always, if you have any questions please ask away in a comment or on Tw*tter, the link is below the giant picture of my face.

– James

Refernces

Bae, C.J., et al., Modern human teeth from Late Pleistocene Luna Cave (Guangxi, China), Quaternary International (2014), http://dx.doi.org/10.1016/j.quaint.2014.06.051

Liu, W., Jin, C.-Z., Zhang, Y.-Q., Cai, Y.-J., Xing, S., Wu, X.-J., … Wu, X.-Z. (2010). Human remains from Zhirendong, South China, and modern human emergence in East Asia. Proceedings of the National Academy of Sciences of the United States of America, 107, 19201–6. doi:10.1073/pnas.1014386107

Reyes-Centeno, H., Ghirotto, S., Détroit, F., Grimaud-Hervé, D., Barbujani, G., & Harvati, K. (2014). Genomic and cranial phenotype data support multiple modern human dispersals from Africa and a southern route into Asia. Proceedings of the National Academy of Sciences of the United States of America, 111, 7248–53. doi:10.1073/pnas.1323666111

University Of Utah. “The Oldest Homo Sapiens: Fossils Push Human Emergence Back To 195,000 Years Ago.” ScienceDaily. ScienceDaily, 28 February 2005. .

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4 Comments

  1. Hi! Got linked to this blog via reddit and have enjoyed reading through your posts. I also saw that you are studying/have just completed the MSc in Human Anatomy and Evolution at Hull York. I’ve been accepted for that course (Archaeology undergrad, focus on human origins) but am having trouble making a decision between the different Masters programs I’ve been accepted to. Although I may need to defer (long story) I still want to make my final decision in the next few weeks so as to not keep unis waiting on me.
    I was wondering if you had time for me to ask you a few questions about the course? It’d be really great to get some insight from someone who has taken the course. I don’t mind carrying out the conversation over email, reddit, etc. if you’d rather not discuss this on the blog page.
    Emily

    1. Hi Emily 🙂 Hooray for Reddit! That must be a new link – certainly one that I had nothing to do with so that’s cool.
      Of course, I’m more than happy to answer any questions you’ve got. Just drop me an email at jameslumbard@msn.com.

      – James

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