Humanity is characterized by a distinctive array of cultural and genetic attributes that differentiate us from our ancient ancestors. Recent research indicates that several critical divergences may date back to an earlier period than previously believed, suggesting a closer relational dynamic between modern and archaic humans, including our extinct kin.

“Our findings advocate for the understanding that Modern and Archaic populations represent variants of an overarching human species, each having independently developed mutations and cultural advancements,” writes a research team led by biologist Luca Pagani from the University of Padova, Italy.

The study meticulously examined genomic data derived from Neanderthal and Denisovan fossils alongside modern human samples, focusing on essential chromosomal rearrangements and genetic variations.

One significant alteration they explored is the translocation of the human PAR2 (pseudoautosomal region 2), a crucial exchange at the extremities of the X and Y chromosomes. This translocation occurred relatively recently in primate evolutionary history, enhancing reproductive success and genetic stability in males—traits vital for the longevity of any species.

Coupled with the major reorganization leading to the formation of human chromosome 2, these alterations distinguish humans from their ape and chimpanzee relatives. Tracing the lineage of today’s Y chromosome reveals its last common ancestor emerged a little over 300,000 years ago, long postdating our divergence from Neanderthals.

A pivotal inquiry arises: did the transformations within the PAR2 region that heralded modern human evolution occur before or after the separation of Neanderthals and humans?

The researchers mapped genomic data against key evolutionary milestones: 1) a population bottleneck approximately 900,000 years ago; 2) the branching event leading to Neanderthals, Denisovans, and modern humans around 650,000 years ago; and 3) the genetic reintegration of Neanderthals into modern human populations about 350,000 years ago.

The authors contend, “If one seeks a moment that signifies the inception of the human lineage, it encompasses the chromosome 2 fusion and the PAR2 translocation.” They also highlighted mutations in the Y chromosome’s PAR2 absent from the X chromosome, which elucidates the timing of the translocation event’s common ancestor.

Significantly, the analysis revealed that the PAR2 alteration predates Event 2, the widely accepted timeline for the divergence of Neanderthals and modern humans. Consequently, crucial genetic traits that characterize us may extend back further into history than previously acknowledged.

By synthesizing various genetic lines of evidence, the researchers assert that we can nuancedly categorize the attributes defining ‘modern humans’ within an evolutionary context.

In summary, the origins of traits that distinguish us as humans likely trace back nearly a million years. Since that period, multiple cycles of population expansion and contraction, alongside significant cultural influences, have contributed to our distinct separation from Neanderthals and Denisovans.

The research indicates functional variations across 56 genes distinguishing modern humans from our ancient relatives, emerging soon after Event 2; most of these traits, particularly those related to cranial and cognitive functions, were not reintroduced to Neanderthals during their interbreeding with Homo sapiens in Event 3.

This may result from population dynamics or sociocultural structures, prompting renewed contemplation concerning the extent of our divergence from Neanderthals. While this study does not provide unequivocal answers addressing our distinctions or delineating human species classifications, it intimates that our shared heritage with archaic humans is more substantial than traditionally perceived, warranting a reassessment of these distinctions.

Although still pending peer review, the study is accessible on the preprint server bioRxiv.