A team of palaeontologists at the University of Malaga have revealed that human evolution is caused by increasing brain size and the acquisition of an increasingly juvenile cranial shape.
Published in the scientific journal PeerJ, the discovery follows research that has been under development since 2015 by the UMA. Scientists were analysing four new human skull specimens: Australopithecus anamensis, Australopithecus prometheus, Homo naledi and Homo longi.
The new research adds juvenile skull samples of modern great apes and brings an innovative approach to our understanding of human evolution. Focusing on the development of the brain, the researchers examined developmental processes in the size of the brain and how this differed between ancestral and derived species.
Human evolution: similarities to apes
The new data reveals that the causes of human evolution are shared with our close ancestors: orangutans, gorillas and chimpanzees and all creatures share the Homo gene, as well as the australopithecine species.
The palaeontologists analysed a negative growth of the cranial vault, which measures brain development, and a positive growth of the dimensions of the face in all species.
Juan Antonio Pérez Claros and Paul Palmqvist, authors of the paper, explained: “This means that bigger crania present higher relative sizes in the face and more reduced sizes in the cranial vault.”.
Further brain development in humans
The researchers found that while human evolution followed the same development as that of apes, human skulls went under a series of lateral transpositions.
Claros and Palmqvist said: “The developmental trajectory of the genus Homo turned to a new starting point, where adults retained the characteristics of the infant crania of the ancestral species.”
These transitions led to a ‘juvenilisation’ of human skulls, a process known as paedomorphosis, which played a crucial factor in human evolution. The changes meant that human skulls developed more in their evolutionary lineage compared to similar species.
The final part of the research looked at the oldest records of human skulls and compared them to more recent specimens. Palaeontologists discovered that the skull of Homo naledi, which evolved less than 300,000 years ago, showed similar proportions to the first human species of Homo habilis, which are more than two million years old.