Posts Tagged 'Ralph Holloway'

Naledi

Ralph Holloway and colleagues have just published a paleoneurological study of Homo naledi. They used seven cranial portions from at least five individuals to provide a general view of an endocast of this species. The study is comprehensive and very detailed, indeed. It turns out that, despite the very small endocranial volume (about 500 cc), the brain general organization is very similar to all the other human species. Beyond some particular features in Neanderthals and modern humans, all human (Homo) species display the same general sulcal pattern. If there were differences in their sulcal organization, these should have been pretty minor or hardly recognizable on an endocast, at least according to what we can test with the small samples generally available in paleoanthropology. So, it is not surprising that Homo naledi has a Homo brain form. But the interesting thing is the association between a human brain morphology and a small brain size, as suggested by this current study. If true, we have two main conclusions. First, our brain cortical complexity and our large brain size are two independent features. They have evolved together in many cases, but not in others. Second, our human cortical folding scheme is not simply an allometric (scaled) version of the apes’ one. Cortical folding is largely influenced by mechanical factors, most of all size-related effects, so one could think that our brain morphology, although distinct from apes, is a secondary consequence of having a big brain. The results presented in this study suggest that this is not the case. We humans have a specific cortical organization and, furthermore and additionally, a big brain too. Reasonably, both features have an influence on our cognitive capacities.

Of course, these results must be confirmed on a larger perspective. Remember that here we don’t have a “brain”, but some scattered endocranial surfaces of a few specimens. That’s not sufficient to reach detailed and reliable conclusions on the brain itself, not to say on cognition. Also, the species Homo naledi (and its chronology) is at present strictly associated with one specific site and needs further corroboration from a wider geographical scenario before supporting firm or generalized statements. Its striking feature is the very small brain size. In this sense, it is worth noting that we often use to mention “average” values, sometimes forgetting about their associated variation and variability. We modern humans have a normal cranial capacity spanning a range of more than 1000 cc. In this paper, Holloway mentions the case of Homo erectus, spanning from 550 cc to 1200 cc. Therefore, caution is still necessary when interpreting the small brain size of these individuals. Of course, the fact that this species (as the Flores hominid) could have undergone brain size reduction or small brain retention does not point against the importance of brain size and encephalization. According to the available fossil record, most human species bet on big brains. Exceptions are expected, but do not break the rule.

I want to focus on one more aspect of this article. Although the topic was definitely “sexy”, the authors avoided any speculation on cognition or phylogeny. Such attitude is so professional and definitely welcome, thank you!

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At Holloway’s

Ralph Holloway is at the Columbia University (New York) since 1964. More than half century dedicated to paleoneurology, brain evolution, fossils and endocasts. Some weeks ago I was visiting his laboratory, an amazing place, full of books, experience, and history. And collections. Endocasts are everywhere, witnessing at once the evolution of the human brain and the evolution of the moulding techniques. So I took the opportunity to ask Ralph some quick comments for this blog …

Why do we still need physical casts? (but do we?)

I think for the most part, we can do very well with virtual endocasts (as long as these don’t get hacked…), although these can never provide the same haptic experience as a true cast, even if it is a good 3D print. At the moment, I am working on LES1, Homo naledi, and while I have a 3D print from scan data of the endocast surface, and good images provided by Heather Garvin, I am making an endocast from a 3D print of the cranial portion, as I need the best resolution I can get of the occipital portion in particular. Even micro-CT scanning doesn’t always provide the subtle variations on the endocast surface that are critical for correctly identifying convolutional details. The downside of course is possible damage to original specimens, and lack of sharing with colleagues at other institutions unless they visit the lab where these are made. Furthermore, the accuracy of virtual endocasts depends on the software, the researcher’s experience, expertise, and whether the algorithms used to correct for distortion, etc, are accurate.

What is the main current challenge in paleoneurology?

The major challenge is to synthesize the overall size data (ECV’s) with whatever sulcal and gyral information (e.g., lunate sulcus, fronto-orbital sulcus, Broca’s cap regions, etc) is available with morphometric analyses for each specimen with temporal and archaeological evidence, so that actual hypotheses can be generated than can be tested within (or even beyond) the paleoneurological community. This requires researchers fully cognizant of anatomical details, and both nonhuman primate and human neuroscience. Needless to say, but many more hominin and hominid endocasts need to be found and studied if paleoneurology is to become a better science.

Advices to those who begin working in this field …

Know your neuro- and cranial anatomies! Stay humble, lose your hubris, and keep in mind how rare endocasts are, and how imperfect these usually are, and how difficult, if not impossible it is to really know what the brain was like when the hominin was alive, and realize that you will probably never see an endocast that fully captures all the convolution details that were part of that once throbbing brain. A lack of hubris will be essential for good science, and don’t dismiss earlier works in paleoneurology simply because these are not modern or based on the last decade of morphometric advances. Staying up to date, or being current with the findings coming out of neuroscience will be particularly difficult.


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