A publication of the Archaeological Institute of America
Ralph Holloway talks about brain evolution and the human mind.
When he was a graduate student at the University of California at Berkeley, Ralph Holloway argued that little could be learned about human brain evolution from studying endocasts, models of the skull's interior. He then spent the next 40 years at Columbia University proving himself wrong. ARCHAEOLOGY'S Zach Zorich spoke with him about what the fossil record reveals about the changing nature of hominid brains.
Holloway in the mid-1980s measuring differences between the hemispheres of an endocast taken from the skull of an Indonesian Homo erectus (Courtesy Ralph Holloway)
Your undergraduate degree is in geology, how did you go from that to anthropology?
Oh, that's complicated. My interest was really in anthropology from the beginning, but my father was not very supportive of the anthropology thing. You have to understand he came out of a Depression-era background and so having a skill that was salable was very important to him, and he didn't think anthropology was it. (laughs) I had been in metallurgical engineering before that and I liked it very much. I wanted to do anthropology but as a compromise I took a degree in geology thinking I could get a job.
How did that go?
I graduated in 1959, and had about a years experience between the oil fields and seismic exploration, and could not get a job. So I ended up in Burbank, California, at Lockheed aircraft doing metallurgical engineering then went to graduate school in anthropology and got out in '64 and immediately had two job offers.
So your Dad was wrong.
Dad was quite wrong, but he died in 1963, so he didn't know about my job offers.
What was it that captured your interest in anthropology?
Evolution, human remains, osteology... (pauses) I've sort of always been interested in mummies. The University Museum in Philadelphia was sort of my playground and they had terrific Egyptian collections and I think that was a stimulus.
What led you to study endocasts?
I needed to do research in order to publish rather than perish. So, I ended up going to South Africa and visiting Raymond Dart and Phillip Tobias at the University of Witwatersrand and I just got interested in endocasts and thought, well, if you concentrate on a few primitive characteristics of the endocast maybe you could make more sense out of it, and that's what I've been trying to do. That's why I really focused on the lunate sulcus [the anterior boundary of the primary visual cortex] for example because if you can define where it is and prove it, then you can really demonstrate that it is an aspect of reorganization. So, that's how I came into the endocast thing.
What are the different stages of human brain evolution?
Well, you can only answer that from the fossil record on the basis of endocasts, which don't give you a complete picture of the brain. But, it is a beginning. Around 3 to 4 million years ago, with Australopithecines, you get a reduction of the primary visual cortex and an expansion of the parietal lobe [[which is involved with visual spatial integration]. At that time, you are dealing with brains about the size of a large chimpanzee's, 400 to 450 cubic centimeters. About 2 million years ago, you get an expansion to about 600 to 750 ccs, and it becomes organized differently, you get cerebral asymmetries and humanlike Broca's regions [which is involved with language processing]. When you get to Homo erectus, about 1.6 million years ago, brain size increases to roughly 1,000 ccs, and the asymmetries between the left and right hemispheres are very like modern humans'. What the fossil record shows is that the basic organization of the human brain took place pretty early on, and after that you have a pattern where the brain increases in size and then reorganizes.
How would an Australopithecine's mind have been different from a modern human's?
Wow, I am having trouble with that one! When I look at Australopithecus afarensis, I don't see the frontal lobes developed like they are in early Homo or modern humans. I doubt they had language. I think their behavior was more like chimpanzees'. On the other hand, were they making stone tools? The earliest stone tools are about 2.6 million years old, which is maybe a little late for afarensis, but not too late for Australopithecus africanus. Making stone tools to standardized patterns is very much a hallmark of human behavior.
What makes you look at a brain and say "this is distinctly hominid."
Well, size is a big consideration. If you look at chimpanzee, orangutan, or gorilla brains, they tend to have flattened and pointed frontal lobes, and when you get to hominids you get a more rounded shape to those frontal lobes, and that's sort of a give away. In hominids you don't have a high degree of what we call platycephaly, or flatness, that you find in other primates. So those are the things you look at, but then you are confronted with LB1 from Flores and its ape-sized brain is like a chimpanzee it is extremely platycephalic and yet the frontal lobes are very different from what you find in a chimpanzee or gorilla so size isn't all, that's clear. Of course, I wouldn't know what to call LB1.
In 2004 a research team working in Indonesia made the controversial claim that the remains of a three-foot-tall adult woman, dubbed LB1, represented a new species of hominid, do you agree with them?
No, I think there is a very good chance that it is pathological, but the final word isn't in on that.
What do you see as the best evidence that LB1 is pathological?
There are a number of things about the post-cranial bones that seem strange: the thickness of the cortex [the outer layer of bone] , the orientation of some of the limb bones, the size is very small, but I'm not a post-cranial expert...you'll want to talk to somebody else about that. But, on the endocast itself I find that the top part and the front part of the frontal lobes have an extremely narrow gyrus called the gyrus recti and those look pathological to me, they don't look like they are extraordinarily re-wired as Dean Falk [the Florida State University anthropologist who analyzed the LB1 endocast] would claim, I've never seen anything like that before, so it seems strange to me. The platycephaly is extremely unusual, the temporal lobes are relatively small compared to the rest of the endocast, which makes me think the virtual endocast reconstruction is faulty, the cerebellar lobes are more wide spread than you see elsewhere, the back part of the occipital sinus has a triangular projection that IÕve never seen before either, so those things suggest to me that this could be pathological. When you compare it to primary microcephalics, however, thatÕs not what you are seeing in LB1. And with new excavations, if they come up with another cranium like this, IÕm willing to say I was wrong, this is a new species.
Brain size is often used as a proxy for intelligence. Is size more important than structure?
I would say they are both very important. But it's a bit of a conundrum. If natural selection favors increased brain size, and it's very important for intelligence, then what is the meaning of the variability of brain sizes that you see in modern populations? Is that related to intelligence?
What's the answer?
To me, it's yes, but that's a conundrum, I can't prove it. I don't know how anyone can say, 'If you increase brain size through the Pleistocene, it's all fine and well, but if you have differences in brain size now it doesn't correlate with intelligence.' Is there a relationship or not? The answer is yes, but we do not know how important the small differences in brain size in modern populations are for intelligence. I tend to doubt that the differences are very important.
When would you say humans first had modern minds?
I think the mind is modern when you get stone tools that are consistently made in standardized patterns. For me, that goes back 1.5 million years to Homo erectus.
Why are stone tools so important?
They show conformity which implies social behavior is being controlled--and that control probably requires language. There is variability in the stone tools, of course. But I'm always impressed by a beautiful Acheulian hand ax that has two or three degrees of symmetry to it. That tells me the maker really had something going on in its mind that encapsulates a bit of art and something else, perhaps, that I can't really define.