Arothron

Arothron (Profico et al 2021)

Arothron is a new R package for geometric morphometrics and virtual anthropology. It is “an R software suite meant to process and analyze digital models of skeletal elements [that] includes tools to digitally extract virtual cavities such as cranial endocasts, to statistically align disarticulated or broken bony elements, and to visualize local variations between surface meshes and landmark configurations”. Among the examples provided in this presentation paper, there is a morphological comparison between the right hemisphere in Neanderthals and modern humans.

Craniosynostotic vessels

Premature fusion of the sutures deforms cranial morphology and disrupt skull organization, with mild to severe effects. The fine morphogenetic balance between hard and soft tissues is altered, generating spatial, structural, and functional conflicts during growth and development. The vascular system is also influenced, suffering consequences associated with oxygenation, thermal regulation, or endocranial pressure. After our extensive survey on the presence and expression of craniovascular traits in normal adult humans, now we have published a study dealing with the same features in craniosynostotic skulls. We considered those craniosynostoses that deform the skulls into a rounder (brachycephalic) and longer (dolichocephalic) shape, and check for differences in the prevalence of endocranial vascular traces commonly investigated in bioarchaeology and paleoneurology. Craniosynostotic skulls display a larger vascular diversity, when compared with normal subjects. The posterior middle meningeal artery is more developed in the dolichocephalic phenotype, probably as a passive consequence of spatial redistribution. The most interesting differences probably deal with the drainage system. The craniosynostotic skulls present a frequent occipito-marginal venous drainage, and larger or more frequent emissary canals. These features are likely to be functional responses to special physiological conditions associated with endocranial pressure and blood flow constraints. Because of their involvement in many structural and functional aspects, these features and their variations have direct implications in human evolution, population biology, and medicine.

Nesher Ramla

A new fossil from Israel: Nesher Ramla. There is a right parietal bone and fragments of the left one (NR-1), and a mandible (NR-2). They likely belong to the same individual. The bones are dated to 126 ka. These fossils display features that are typical of Middle Pleistocene archaic humans (i.e., Homo heidelbergensis and Homo erectus), but with additional traits that can be frequently found in Neanderthals. The parietal bone is large, but with an archaic morphology, if we consider its general form, the bone thickness, the anatomy of the vascular traces, or the gross proportions. A cluster analysis of its principal anatomical features suggests a morphological similarity with Arago. Taking into account its age and the admixture of archaic and derived features, the main hypothesis concerns the possibility that this fossil could represent a remnant population ancestral to Neanderthals. Mosaic evolution is not only an anatomical or taxonomic concept, but has also a geographic aspect, suggesting differential rates and times of change on a spatial (and rather local) scale. Diversity is a multidimensional issue, and any phylogenetic unit has its own evolutionary fingerprint. Here a post by Ann Gibbons, and a commentary by Marta Mirazón Lahr.

Paranthropus

A recent shape analysis on the endocasts of OH5 and SK1585 (two members of the genus Paranthropus) suggests that their overall morphology is perfectly within the range of variation of extant chimps. In contrast, STS5 (a specimen that is representative of the genus Australopithecus) displays an endocranial shape which is intermediate (exactly halfway!) between chimps and modern humans, and out of the range of both genera. Therefore, this similarity between Paranthropus and Pan may suggest a lack of derived endocranial traits in the robust australopiths, at least in relationship to the human lineage. Of course, paranthrops had a very specialized (and odd!) skull, so we must consider that their important bony superstructures may have introduced very peculiar and autoapomorphic constraints in the morphogenetic relationships between face and braincase, influencing the brain gross morphology in some specific regions (like for example, at the frontal lobes).

Galvanic shapes

Silva Gago et al_AJHB2021

Our first research article on electrodermal activity concerned arousal/attention differences when handling different Paleolithic tools. The second was on the influence of hand size and sex. Now, the American Journal of Human Biology has published the last one of the trilogy, on the influence of tool shape. The main geometric features in Lower Paleolithic tools are i) elongation and ii) the position of the maximum thickness. Interestingly, none of these two factors seem to influence the level or arousal or attention when grasping the tools during haptic exploration. The features that trigger an electrodermal reaction are the general tool size (a spatial issue), the tool weight (a gravitational issue), and the morphology of the tool base (a grasping issue). Such electrophysiological responses are supposed to be associated with cognitive brain-body feedback, and possibly with those sensing capacities that support a good prosthetic ability. These studies are part of a wider frame investigating visuospatial integration in cognitive archaeology.

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.


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