This is segment 2 of learning module 13 talking about pre-modern humans So we left off talking about the earliest evidence of Homo heidelbergensis at a site called Bodo in Ethiopia Now I want to continue to a site in Zimbabwe called Broken Hill also in Africa now Broken Hill Is dated to about 130,000 years ago? so we're looking at about a 500,000 about half a million year difference between Bodo and Broken Hill. And at Broken Hill, they found a complete cranium and post cranial remains from several individuals.
So here's the cranium at Broken Hill. And now we see in a space of half a million years, 500,000 years, that we have even more of a trend toward modernity, right, looking at even more gracile features. So still large brow ridges, but less than what we saw at Bodo. Still pretty significant, though, if you compare it to modern humans. Even more rounded brain case, though.
Now we're getting this more kind of tucked in feature, right? You see this sort of globular shape forming. Not as much verticality as you would see in modern humans, but plenty of vertical expansion in the top of the cranium.
We're getting more tucked in. in a more rounded occipital bone that's the bone in the back of the cranium more roundedness in here and you can see kind of like the face is more tucked under the cranium sort of less oval although more oval than you see with modern humans but less so than you see with let's say Homo erectus or early Homo or much less the australopithecines so much more roundedness going on here and I think overall you can see a trend toward more delicate bones than you might see with let's say homoerogaster or homo erectus. Okay, still somewhat noticeable nuchal torus. If you recall the nuchal torus is the cranial base ridge and it's this ridge back here where the neck muscles attach to. If you recall in Osteopithecus we noted that the nuchal torus, the cranial base ridge, was quite large.
And that is really ancestral to quadrupeds, right? Because quadrupeds need huge neck muscles in order to lift their big crania. As walking quadrupedally, they need huge neck muscles. And so that's evident through the nuchal torus. However, humans do not have a large nuchal torus.
If you feel up under your cranium, down there at the base of your cranium, do you feel a large... bump or a large ridge? Not usually. Modern human populations might feel a very slight ridge or very very slight couple of bumps on the cranium down in the back where the neck muscles attach.
You can really feel where those attach by if you move your head up and down you can feel your neck muscles move and as they attach to the cranium you can feel where they attach. So if we don't really have much of a nuchal torus we talked about how homo erectus has still a fairly large cranial base ridge, not as much as the australopithecines, not as much as let's say chimpanzees or gorillas, nowhere even close to that, but still a little bit larger than humans, indicating that they have somewhat larger neck muscles. And this makes sense actually that if you have kind of an ovular cranium, You're going to need a little bit larger neck muscles to move the cranium around. One of the reasons why we have really wimpy neck muscles is that the modern human crania are very globular.
And so it's pretty much perfectly balanced on the cervical vertebra. So we don't need large neck muscles. But the more prognathism you have, the more ovular your cranium is, the more...
Like the slightly larger neck muscles you need in order to move the cranium around so we see with Heidelbergensis they still have somewhat noticeable nuchal torus but at this point it's it's more ancestral really than it is adaptive because We're seeing that Homo heidelbergensis at least 130 thousand years ago. Look how vertical the face is we're looking at very low degree or no degree of prognathism. So that is a much more modern trait. And you can really see that within a span of 500,000 years, how Homo heidelbergensis is really this transitional point between Homo erectus and modern humans. So we talked about...
Homo erectus as being good evidence, transitional evidence between, let's say, the early hominids and modern Homo sapiens. Now we're looking at sort of the midpoint between Homo erectus and modern Homo sapiens. All right, so lots of evidence of transition as we go along here in our evolutionary journey. Continuing on, I want to take a look at some evidence in Western Europe, because we haven't really been able to see any specimens coming out of Western Europe, as mentioned. the whole area was covered by glaciers up until about 700,000 years ago so there's no evidence prior to Homo heidelbergensis in the area.
You see no evidence of Homo erectus in Western Europe. So now we're presuming that early H. heidelbergensis made it into Western Europe Homo heidelbergensis having evolved out of Homo erectus and and now takes habitation into Western Europe.
Okay, we're going to look at a site called Atapuerca in Spain so all the way in the far western Europe and this is what is found at Atapuerca. So at Atapuerca there are several complete crania the remains of at least 28 individuals, okay, so we're talking about Crania of a few individuals, but then post cranial remains of at least 28 individuals Which we're now getting into a time period that has much better Preservation and we're going finding a lot more evidence here So at Atapuerca they find that three hundred thousand years ago, and I like to use this example because three hundred thousand years That's right in the middle between basically Bodo and Broken Hill Bodo was at six hundred thousand years ago Broken Hill is at 130,000 years ago, so now we're right in the middle 300,000 years ago. What do we see in between?
Here we see thick cranial bones that robusticity continues Rounded occipital bone. Okay. Now we're starting to see a little bit more roundedness than we saw even with Bodo the expansion of the parietals so the parietal bones are these side bones of the cranium So the side panels of the brain case are called the parietals. So to recap, the top is the sagittal bone, the back is the occipital bone, and then the sides of the cranium are called the parietals.
The parietals are more expanded in homohydral bergensis than you see in homo erectus. So again, lending towards that width at the top of the cranium above the ear holes. Then large brow ridges continue. Brain size over 1100 cc's, reduced tooth size.
So we're seeing even more reduction in the teeth that is compared to Homo erectus, which if you recall, Homo erectus had a dentition that's fairly similar to humans, just larger overall. Now we're looking at Homo heidelbergensis, really looking at teeth that are fairly similar to modern humans. So if heidelbergensis walked into a dentist, the dentist probably wouldn't freak out.
They might notice some slight differences, but overall it would look very similar to human dentition. Very diminished nuchal torus. Okay, so at least in Spain, we're seeing not a lot of evidence of a nuchal torus or cranial base ridge.
A little bit of prognathism, similar to homo erectus. I think this is a great example to show how you can have these sort of local variations where you have like sort of a different mix of both modern and primitive traits, depending on that population, right? So we might see a little bit more modernity in certain areas, less modernity in other areas.
But there's enough variation that is due to these local populations and the effects of things like gene flow and genetic drift or having a big... impact on the variation that we see in traits. But the important part is that they're more alike than they are different. So in other words, paleoanthropologists have seen these differences as more being variations of the same species than really different species. Sort of that whole lumping thing versus splitting thing that I've discussed previously.
And in this case, it looks like Homo heidelbergensis has similarity of traits in various parts of the old world. that paleoanthropologists are more inclined toward lumping all together into the same species, which isn't just about similarity of characteristics, but it also has to do with reproductive ability. This is going to be a big issue when we get into the last couple of learning modules, when we talk about Neanderthals, when we talk about modern humans.
that talking about reproductive ability, whether they were able to reproduce or not. These are big questions for ultimately understanding our family ancestry. All right, continuing on, we're going to take a look, go all the way across the continent to eastern China.
I'm going to compare a couple of specimens in China, one from Dali in China and then Xinyushan in northeastern China. and they're both more or less contemporaneous to each other, but we're going to see some slight differences here. So at Jingyushan, there was found a cranium, and then also at Dali.
So here's a comparison. At Dali, which is dated to about 230,000 years ago, Jingyushan is 200,000 years ago. So we're looking at a time difference here of about 30,000 years, which is... pretty close in time.
But we do see some differences. So at Dali, brain size 1120 cc's and the sagittal ridge is apparent on both the Dali specimen and the Xinyu Shan specimen. Now we talked about Homo erectus having a sagittal ridge and we do not really see a sagittal ridge at all in Bodo specimens or Broken Hill. The adiportica specimens, none of them have a sagittal ridge anymore. So they don't have that thickening of the bone at the top of the skull, which indicates slightly larger jaw muscles.
So that's a trend toward modernity, but it seems these eastern specimens, these Chinese specimens, do have that slight thickening at the top of the skull that indicates larger jaw muscles. So what's going on here? We're looking at, is it adaptive in some way? For some reason, Homo heidelbergensis needs larger jaw muscles because of diet.
Or are we looking at here that we know that Eastern Chinese specimens of Homo erectus had a sagittal ridge? Are we just looking at that Homo heidelbergensis evolved out of... of homo erectus in eastern china and that they have the retention of this ancestral trait so it's sort of hard to know exactly but again we're looking at a little bit of local variation but the walls of the brain case are thin like homo sapiens so it's this interesting mix right sagittal rage is sort of more primitive trait but this gracility of the cranium is more of a modern trait so sort of an interesting mix then um the literature also you talks about how the Dali specimen has what are termed flattened nasal bones.
Now, if you recall, in modern humans, we do not have flattened nasal bones, really. They're kind of part of this whole slight projection that happens as a result of our reduced prognathism. So if you look at the profile here of humans, the nasal bones kind of project out a little bit.
and then the rest sort of is directly under the nose, the nasal area. However, in chimpanzees, you have flattened nasal bones because the lower part of the face, the snout area, comes out in what we term prognathism. So it sort of just smoothly goes into prognathism. If you look at...
this specimen from Dali, you can see that they are a little bit flattened here, which is sort of not what you would expect with a specimen that's more recent in time. So the literature points this out, but I do want to say that although this seems like a primitive trait, we do have to keep in mind that this is just one individual, and it doesn't seem like that the... Other specimens of this time also have this trait.
So I would be inclined to say that, you know, if we saw a whole trend of this, that this is really a thing. But it could just be this particular individual. But one last thing is that the brain size does seem to jump from 1120 to 1260 cc's in just about 30,000 years.
So we do see an increase in cephalization. This could just be differences in individuals, or it could actually show exactly when there is a jump in encephalization in a short period of time. All right, we'll continue with homohydrobrigensis in segment three, so please follow me there.