About 70 thousand years ago something happened that resulted in modern humans. Whatever caused this change, it resulted in what appears to have been a major leap in cognitive capabilities. It was quite possibly the change that most differentiates us from Neanderthals and other archaic humans and what has made us unique among hominid apes.

While anatomically modern human skeletons can be found dating to 200,000 or more years ago, we do not find broad evidence of sophisticated tools, artwork, and ornaments until around 70,000 years ago in Southern Africa. This period is just before a migration of humans first from Southern Africa to East Africa and the later migration of humans, which can be genetically linked to all modern humans, from East Africa to the rest of the world. We have multiple lines of evidence – linguistic, paleontological, and genetic – pointing to humans who are the ancestors of modern humans from this time and these places. In addition to better capabilities to survive and exploit any ecological niche, quite possibly these humans had superior weapons, greater organizational ability for warfare, and possibly even a greater propensity for warfare. I believe they may have lived in larger groups than other humans at that time. In the next 30-40,000 years these humans displaced other archaic humans, killed off the megafauna, and spread rapidly to Asia, Europe, Australia, and eventually the Americas. In the process, humans proved themselves able to survive in almost any environment from the cold reaches of the far north to the heat of the tropics, from deserts to rain forests, from mountains to the ocean.

The secret to this change could not have been a larger brain. By the time of appearance of the first anatomically modern humans, brain size was already the same as modern human brain size. For that matter, the brain size of Neanderthals was larger. This change occurred without a major change in anatomy so it must have been relatively subtle. We might suspect the change to involve language capabilities but that doesn’t resolve what exactly triggered the change to come about. Was it a random language gene mutation? Or was it some broader change that might affect a range of cognitive abilities?

We are now getting hints that the change that resulted in modern humans is linked to changes in the maturation rate of the prefrontal cortex (PFC). The change is a delay in the time required for the PFC to fully develop. This extended period of development meant that synaptic connections formed over a much longer time period and, we might logically assume, formed during extensive social interaction.

Evidence from a 2012 study Extension of cortical synaptic development distinguishes humans from chimpanzees and macaques suggests that a delay in the maturation of the PFC is a key feature that distinguishes humans. The contrast in development time of the prefrontal cortex between humans and other apes is quite remarkable. The time of peak expression of synaptic genes in the PFC is less than one year in chimpanzees and macaques, but around five years in humans. Although there may have been a gradual lengthening in PFC maturation during earlier human evolution, the study authors believe the major change occurred sometime after the human Neanderthal split. The study suggests, in addition, that it was likely Neanderthals had a maturation time more closely resembling apes than humans. This provides more evidence that this PFC maturation delay may be key to human cognitive abilities and behaviors.

Isolating the change in PFC maturation to a time around 70,000 years ago is a paper by Andry Vyshedskiy.

Our research into evolutionary origin of modern imagination has been driven by the observation of a temporal limit for the development of a particular component of imagination. Modern children not exposed to recursive language in early childhood never acquire the type of active constructive imagination called Prefrontal Synthesis (PFS). Unlike vocabulary and grammar acquisition, which can be learned throughout one’s lifetime, there is a strong critical period for the development of PFS and individuals not exposed to recursive language in early childhood can never acquire PFS as adults. Their language will always lack understanding of spatial prepositions and recursion that depend on the PFS ability. In a similar manner, early hominins would not have been able to learn recursive language as adults and, therefore, would not be able to teach recursive language to their children.

I think linking the delay in maturation of the PFC to modern language capabilities makes a lot of sense as well as tying recursion to the broader PFS capability. We know children not exposed to language at critical times in development do not ever acquire good language skills. Likewise, we know children exposed to multiple language from an early age learn to speak as natives and that the older we are before exposure to a new language the harder it is to pick up the language. Vyshedskiy himself points to individuals with PFS deficits associated with damage to the PFC. Since our best estimates for origins of modern languages and modern human behavior as expressed by artwork and ornaments tie to the same time, it makes sense to link all these things together.

Vyshedskiy goes on to hypothesize a somewhat complicated scenario that I won’t get into about how all of this came about around 70,000 years ago.

I think the picture how all of this came about might be straightforward.

Let me speculate that sometime early into last glacial period, perhaps about 100,000 years ago, numbers of humans migrated to Southern Africa in response to climatic changes. There they developed stable, non-nomadic settlements based extensively on shellfish. Settlements such as that would almost be prerequisite for allowing for a slower PFC development. We have evidence of widespread consumption and transport of shellfish from this location. Shellfish are rich in iodine and fatty acids which increase dopamine activity. Dopamine is heavily involved in the PFC and would be essential for reinforcing PFC reward-based social learning. At that point, seemingly the stage would be set to allow a gradual increase in PFC maturation time. The increase in maturation time could have been caused either by a single mutation or perhaps even by preexisting but initially not widely distributed genetic traits. In an environment such as this, feedback from the social learning from one generation to the next could have slowed the development of PFC to allow for additional social learning. Outgrowth of the social learning would be new cognitive skills for language, imagination, art, social control, and behaviorally modern humans.