New findings on the evolution of the skull in the human lineage

Recent research reveals new details about the evolution of the human skull and brain.

The new study, carried out by two paleontologists from the University of Malaga (UMA) in Spain, has just revealed that the evolution of the human lineage combines, in a unique way, an increase in the size of the brain with the acquisition of an increasingly juvenile form of the brain. skull.

This work is the result of a line of research already initiated in 2015 by the UMA, which adds the analysis of four new hominin skulls from specimens discovered later: ‘Australopithecus anamensis’, ‘Australopithecus prometheus’, ‘Homo naledi’ and ‘ Homo longi’. In addition, non-adult specimens of modern species of great apes have also been incorporated.

Likewise, the research provides a novel approach in the interpretation of hominization in terms of embryonic development, which refers both to changes in the start or end times of development processes and to differences in the rhythm of these between an ancestral species. and another derivative.

Cranial evolution: humans and apes

Thanks to these new analyses, it has been possible to verify that the representatives of the genus Homo, as well as the australopithecines -our sister lineage in evolution- share with the orangutans, gorillas and chimpanzees a negative growth of the neurocranium -the cranial vault, which measures the brain development, grows at a slower rate than the rest of the skull- and, also, positive of the splanchnocranium – the dimensions of the face, correlatable with the size of the dentition, which grow faster in development-.

“This means that larger skulls have higher relative proportions of the face and smaller relative proportions of the cranial vault,” explain professors from the Faculty of Sciences Juan Antonio Pérez Claros and Paul Palmqvist, authors of the study.

Photographic representation of the four new hominin skulls analyzed in the study. (Image: University of Malaga)

Greater brain development

Both experts point out that, while in the case of australopithecines, cranial evolution follows the same scaling during development as in apes, in humans, a series of lateral transpositions also took place.

“The developmental trajectory in the genus Homo shifted to a new starting point, retaining in the adult features of the infant skulls of the ancestral species,” they say.

As they indicate, these changes involved a “juvenilization” of the cranial proportions, a process known as paedomorphosis -in the form of a child-, which allowed greater brain development in our evolutionary lineage in relation to other species.

Finally, it has been shown that the skull of Homo naledi, despite being a relatively recent species in the fossil record of human evolution -less than 300,000 years old-, shows proportions similar to those of the first representatives of the human genus, Homo habilis, more than two million years old.

The study is entitled “Heterochronies and allometries in the evolution of the hominid cranium: a morphometric approach using classical anthropometric variables”. And it has been published in the academic journal PeerJ. (Source: UMA)