Dmanisi

Marcia Ponce de León and colleagues have now published a very comprehensive study of the endocasts from Dmanisi. The article includes a part on sulcal patterns and brain-skull relationships, and a part on endocranial shape variation. The endocast shape analysis is very extensive, on apes and humans, a valuable study in paleoneurology, indeed. It gives an inclusive view of the endocranial variability in hominoids, at both intra-and interspecific level. In this shape analysis, the Dmanisi endocasts show a morphology definitely within the early human range (Homo ergaster/erectus). The sulcal analysis shows, instead, that the Dmanisi precentral sulcus crosses the coronal suture, as in apes, while in humans it is positioned behind this cranial reference. They conclude that the Dmanisi people (and hence early Homo) had not evolved a large frontal cortex (possibly, a lack of expansion of the Broca’s region). So, they suggest that an expansion of the frontal lobe happened after the origin of our genus. Such expansion, associated with later hominids after 1.5 My, would have involved the frontal and the parietal lobes at once.

The spatial relationship between the brain sulci and the skull bones is a very interesting topic, because of its relevance in functional craniology, and because it is something that can be directly investigated in fossils. However, it must be taken into account that the spatial relationships between skull and brain are not only due to brain anatomy, but also to multiple factors (facial development, cranial base flexion and so on) that generate a large and complex set of spatial constraints. In fact, the same team published two years ago a study suggesting caution when considering together the cranial and cerebral landmarks to make paleoneurological inferences. The frontal lobe morphology is precisely a good case-study, because it is influenced by the spatial relationships with the orbits and upper face. Wider frontal lobes in modern humans and Neandertals could be, for example, a structural consequence of having the frontal cortex right above the orbital roof, and not a sign of real neurobiological changes. It is not trivial, in this sense, that the endocasts from Dmanisi, although having such a plesiomorph pattern between sulci and suture, then display an overall “human-like” brain geometry. This relationship between the precentral sulcus and the coronal suture is really interesting, but maybe more caution should be put when giving for granted that it is due to brain cortical evolution alone. Needless to say that, furthermore, the taxonomy of Dmanisi is still uncertain. There are still doubts on whether they are all from the same species, or even whether they are really part of the human genus. Here a commentary by Amélie Beaudet, a latest news article by Michael Price, and a ScienceNews post.

Extinctions

Insisting on a cognitive equivalence between modern humans (Homo sapiens) and Neandertals (Homo neanderthalensis) probably means neglecting the differences between a flake and a pendrive, or between a wall scratch and the Sistine Chapel. Also, insisting on a cognitive equivalence between two species that have evolved separately for hundreds of thousands years probably means neglecting evolution itself, suggesting that no changes did occurr in that long time, or that – magically – the two lineages underwent the same cognitive modifications. Unlikely. The idea of cognitive equivalence is often emotionally defended because it is implicitly assumed that, if not equal, one should be better than the other. In this case, the problem may regard an inadequate awareness of the principles of evolution, which engenders a problematic confusion between biological diversity and moral judgement. In general, our society suffers a profound misperception of diversity in terms of ethical principles, for example confusing biological or individual differences with social egalitarianism or legal impartiality. It is assumed that diversity implies a different social consideration and, therefore, in order to eliminate social inequality, we have to neglect differences. This position is rather dangerous, because it subtly supports (instead of contrasting) the association between biological equality and social rights: if you want me to respect you, then you have to demonstrate that we are the same. The hazardous message here is: we only respect those who are like us. Besides the risks associated with this perspective, it usually never works well because differences are there, and they can’t simply disappear with the application of a dogmatic mantra. Rejecting diversity is a standard approach adopted to strengthen group affiliation (it is easier to reinforce a group because of the differences with other groups than by finding affinities within the group itself – that is, it is easier to build membership on hate, than on love!). However, this is more understandable if you are a boar or a baboon. Instead, an ape with 1350 cc of brain mass should be able – in theory – to handle diversity more fruitfully, going beyond ancestral emotional limitations. Far from the superficial equality mantras circulating nowadays, during the 70s, there was a very good feminist slogan which stated: equality as a human right, diversity as a human value. Correct.

The idea of a cognitive equivalence between modern humans and Neandertals is then probably an attempt to avoid promoting the idea that Neandertals were dumb, superficially assuming that “different” necessarily does mean “stupid” or, at least “less than”. Nonetheless, it is worth noting that while defending the pride of the Neandertal cognition, most theatrical views keep on suggesting that their extinction was due to a lost battle (ecological or even physical) with the smart Homo sapiens. Of course, despite the enduring approval of this interpretation in books and newspapers, there has never been any scientific evidence to support it. Maybe there was a competition (ecological or even physical) between the two species, or maybe Neandertals simply went extinct as usually does happen in evolution, and we modern humans have then colonized new empty spaces. Tens of hypotheses have been presented to explain the Neandertal disappearance, but most of them can’t be even tested in a proper scientific way. Therefore, they should be frankly relegated to the realm of the personal opinions.

Now, two archaeologists and one psychologist have published the results of a survey on more than 200 researchers involved in human evolution. The survey asked about the personal opinion on Neandertal extinction, adding some tests on the socio-political orientation of the participants. Results suggest that most scholars point at demographic reasons as the most probable cause of Neandertal withdrawal from the phylogenetic scene. Thus, a Neandertal personal problem. Environmental effects or the competition with other humans are reasons which, albeit deserving attention, do not receive consistent support from the scientific community. Interestingly, different positions in this debate are not associated with specific socio-political profiles, and hence they deal with a personal scientific view rather than with gross (traditionally right-left) prejudices.

This survey is undeniably useful for several reasons. First, if the sample is sufficiently representative, now we know what most researchers think about Nendertal extinction. Second, it is a nice case study to analyze whether and to what extent some kinds of behavioral preconceptions (in this case, socio-political affinity) can influence academic position on a scientific topic.

However, there is a third aspect that is pretty crucial. If most paleoanthropologists think that Neandertal extinction is probably associated with an internal (demographic) limitation of the species … why is competition with modern humans still the most cited possibility in popular science and journalism? The answer, as you can imagine, could be rather easy: because the competition issue is more attractive, because it is good for marketing, because it is more suited for an epopeic tale, and because it is more glorious for the species’ ego. All this suggests that, basically, paleoanthropology is a field still influenced by a certain necessity of storytelling, and that there is a certain separation between academy and society. The necessity aspect is generalized: the community needs stories, journalists sell stories, the academy supplies stories. All the parts agree on this reciprocal trade. The separation aspect is an evolution of the ivory tower refuge: only those scientists that accept to tell stories will be allowed to go out, the others will be locked in.

In sum, it seems that in paleoanthropology, we still have some unresolved conflicts of interest. On the one side, we have a part of society neglecting differences, and at the same time another part renting science to narrative. Probably, neither of these two strategies is of great help for science and knowledge. Nor is it useful for a healthy cultural development. There is a refrain: humans are the only animal that stumbles twice on the same stone. In the case of fossils, we can maybe add that they also seem to keep on stumbling on the same bones.

Asymmetries, encore …

I had missed this further study on endocranial asymmetries. The issue is central in brain evolution because hemispheric asymmetries has been since ever interpreted as a specialized human feature. Endocranial asymmetries, used as proxy for brain asymmetries, are then generally used to investigate this character in fossils. Different scholars have supported different conclusions on this matter. It has been suggested that hemispheric asymmetries are specific of humans (with relevant evolutionary implications), that the difference is only a matter of degree (humans would hence have just more asymmetries than other primates, but of the same nature), or that humans are more asymmetric only because of a larger brain size (allometry). These alternatives are then mixed with causal hypotheses involving genetic aspects, structural adjustments, or neural plasticity. As for many other paleo topics, anyone has a personal recipe on how we can interpret these phylogenetic similarities and differences. And, importantly, on how to measure them. The issue of measurement is not secondary, because we are dealing with smooth, blurred, and tiny morphometric features, not easy to detect (and to quantify) at all. In this new study, Simon Neubauer and colleagues employed an elegant and complex set of mathematical adjustments to compare both the kind and degree of endocranial asymmetries in humans and apes. According to their results, chimps are less asymmetric than humans, but orangs and gorillas display a human-like pattern of asymmetries. Or, we should say, an ape-like pattern of petalias (the gross right-left endocranial asymmetries). These differences are due to size variation only to a limited extent, suggesting that asymmetries could be a functional thing, and not an allometric consequence of large brain volumes. The occipital asymmetry stands as the most noticeable one, in both humans and apes. With all this in mind, it is anyway useful to recall two main points. First, when dealing with the human genus (Homo), all human species are known to display the modern (Homo sapiens) pattern. So, whatever the conclusions on this topic, it does not add to major questions internal to the evolution of our own species. The fact that the modern pattern of endocranial asymmetries is shared within all the human genus is something known since long ago, although many scholars keep on discussing this aspect in any new fossil specimens, as it would be of any interest (I guess that they found the topic academically “sexy” for media and colleagues, but it is actually like one would stress, at any new fossil hominid discovery, that the individual had two legs). Second, it is necessary to remember that we still don’t know what is the biological relationship between those macroscopic skull asymmetries and the corresponding histological brain asymmetries. Those endocranial asymmetries are due to differences in brain mass, neurons, neural connections, blood, cerebrospinal fluid, cranial constraints, genetic programs, biomechanical tensions, and a large series of morphogenetic factors. To date, the underlying mechanisms generating those subtle differences are not known, and a direct association between endocast asymmetries and brain asymmetries may be a risky (and hasty) speculation.

The fate of Middle Pleistocene

My welcome for the new year is a perspective review entitled “Evolving human brains: paleoneurology and the fate of Middle Pleistocene“. The article introduces human paleoneurology and functional craniology, and a topological model of the skull-brain network system. Then, I discuss the paleoneurological variations associated with Middle Pleistocene, and the following fate: modern humans and Neandertals. Finally, in this article I provide a further development of my hypotheses on cognitive extension and prosthetic capacity, according to the evidence associated with the evolution of the parietal cortex. The article is published as part of a special issue of Journal of Archaeological Method and Theory, edited by Marlize Lombard and Anders Högberg and entitled “Theoretical pathways: thinking about human endeavour during Middle Stone Age and Middle Palaeolithic”. Here a full-text view-only version of the article.

Extending the body into digital technology

***

Here above the full video of the Round Table “Extending the body into digital technology: an evolutionary perspective“, organized by Claudio Tuniz and myself at the recent EuroScience Open Forum 2020 (Section: I compute therefore I am). Here the Program of the meeting, and the complete Programme Book. The conference includes a talk of mine on paleoneurology and visuospatial evolution, a talk by Atsushi Iriki on extended body and environment, a talk by Luke Miller on extending tools into the self, and one by Barbara Pernici on chess and technology.

Florisbad

The skull of Florisbad was found in 1932 in South Africa, and it is dated to about 260 ky. It could belong to a very early Homo sapiens population, to a derived stage of H. heildelbergensis, or to a side branch of some unknown human taxon. We have now published a report on its braincase, as to present a general view on some metric and non-metric features. The curvature of the frontal squama is definitely modern, suggesting a modern spatial relationship between the face and the neurocranium. Nonetheless, the frontal lobes are very broad, as often observed in Neandertals. In contrast, the parietal regions display a more archaic morphology (in their general form but also in their vascular anatomy), more affine with H. heidelbergensis. There are some individual epigenetic features, (like the interparietal groove) which are generally associated with local changes of the diploic thickness. The mosaic combination of derived and archaic traits hampers a reliable taxonomic assessment of this specimen. Furthermore, all these features are not diagnostic in terms of taxonomy, because they are characterized by noticeable individual variation and idiosyncratic differences. Fossils with distinct admixtures of antero-posterior cranial features (generally, the posterior regions use to be less derived than the anterior ones) have been described in Africa (Jebel Irhoud), Asia (Maba) and Europe (Sima de los Huesos). It can be useful to remind that taxonomic labels are but useful conventional elements aimed at supplying conceptual and lexical tools, necessary to organize our thinking capacity. Our human brains do need those conventional units, but nature, of course, does not.

Krapina

Zachary Cofran and colleagues have just published an outstanding methodological paper presenting new digital reconstructions of the Krapina endocasts, with estimated endocranial volumes. They revise the Krapina specimens for two main reasons. First, they suggest that some previous endocranial estimates for their cranial capacity are questionable, because of the uncertainty associated with the remains, which are fragmentary and incomplete. Second, they recommend to substitute specific values for fossils’ cranial capacity (that convey a – false – sense of precision) with ranges, according to different reconstructions and error. In my opinion this approach, remarkably discussed back in 2012 by Neubauer and colleagues in their study on Australopithecus africanus, seriously represents a main advance in paleoneurology. Estimates for Krapina 3 and Krapina 6, which are the most complete skulls, does not change particularly, when compared with previous values obtained from physical reconstructions of the endocasts. New figures for Krapina 1 and Krapina 5 are provided. A first reconstruction for Krapina 2 is also presented. Estimations are based on endocast morphological interpolation based on geometric morphometrics and shape analysis. Interestingly, using a Neandertal as template (Spy II) seems to work better than using a modern human template. This latter also works fine, but the final virtual endocasts are a bit “modernized”, because the modern template introduces (as expected) a slight parietal and cerebellar bulging. This study also confirms that the Krapina sample (dated to 130 ka) shows a range of endocranial volume (and, possibly, overall brain size) that is similar to the range of Middle Pleistocene Europeans (Sima de los Huesos) and of other pre-Wurmian Neandertals, namely smaller than later classic Neandertals. Here, an old report we published on these same specimens back in 2006, comparing Krapina and Saccopastore.

More precuneus

One more paper on precuneus morphology. The precuneus displays a remarkable (and definitely striking) variation in its size and shape in adult humans. One can think that such geometric diversity is due to cranial deformation and constraints, and not to real (primary) brain differences. And, if real cortical differences are involved, one can think that its longitudinal and vertical extensions are the result of the same process: overall larger (or smaller) precuneus. In this new study, we have analyzed its longitudinal, vertical and lateral proportions, as to see whether there is a unique morphological pattern, or else if those directions of growth are independent. Results support the latter conclusion: its relative development in length is not patently associated with its relative development in height or width. This may suggest that distinct areas (and functions) are involved. And, of course, that such variations are due to real (primary) brain features, and not to (secondary) deformation due to cranial factors. It remains to be evaluated to what extent the grey or the white matter do generate these spatial variations, and which specific areas are involved. The precuneus is much more developed and expanded in humans when compared with other primates, including apes, and its corresponding regions appear also larger in modern humans when compared with extinct human species, including Neandertals. The homology of its areas, when comparing humans, apes and monkeys, remain to be fully understood, although new stimulating information is now available, in this sense. Previous articles on the same topic dealt with precuneus general shape, sulcal patterns, population variability, brain-braincase relationships, primate variations and cortical surface area. Here a review on the evolution of the parietal lobes. The precuneus is mainly involved in visuospatial integration, and it represents a central node for the integration between brain, body and environment, as well as a crucial center for body cognition.

[Full-text View-only PDF]

Hands on the Lower Paleolithic

After our articles on hand-tool morphometrics, on tool handling and electrodermal activity, and on hand morphology and haptic perception in Lower Paleolithic tools, here a new study on ergonomics and finger flexion. By using a digital glove for coordinates, we analyzed the comfortable grasping position in choppers and handaxes. “Comfortable” doesn’t deal with tool functions, but instead with haptic exploration and ergonomics. This is not about using, but about sensing. According to the results, choppers and handaxes trigger distinct patterns of finger flexion. Interestingly, the last three fingers are particularly involved, and not the thumb or the index finger. When we handle a tool, it becomes included into the body scheme at cerebral level, extending our physical body to peripheral elements and adding the tool’s properties to our cognitive system. Therefore, different haptic patterns during grasping can also suggest distinct levels, types or grades of tool embodiment.

On brains and endocasts

A recent article by Dumoncel and colleagues provides an interesting comparison between brains and endocasts from the same subjects. Results suggest that correspondence is pretty good and able to reveal many cortical regions, at least when taking into account the sulcal pattern. The temporal lobes and the frontal regions are the ones with more information. The dorsal regions are instead where endocasts are less reliable, probably because of problems associated with brain deformation, gravity, vessels, or cerebrospinal fluid. The region of the superior sagittal sinus is the most problematic, and the superior parietal surface is often void of traces too (in this article we found the same problems with landmarking). The paper addresses some early disagreements on whether endocasts are a good proxy for brains, discusses major difficulties associated with this field, and reviews new methods for automatic sulcal detection. The study is based on 5 individuals only, but the results are definitely stimulating.


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