What was the shift that made our ancestors band together, craft tools, and develop language all those thousands of years ago? This is a question that has been at the heart of what it means to be human, and the answer to it remains as elusive as ever.
But a new study published this week in the Proceedings of the National Academy of Sciences has come up with a novel proposition as to how we are different from the apes. After studying the brains of 38 primates from six species, including humans, tufted capuchins, olive baboons, gorillas, and chimpanzees, researchers found significant differences in the levels of particular neurotransmitters.
It turns out that compared with other primates, gorillas, chimps, and humans have higher levels of serotonin and neuropeptide Y, but humans also have something else. The human brain showed elevated levels of dopamine not seen in any other primate. At the same time, compared to the chimps and gorillas, humans had lower levels of acetylcholine, a neurotransmitter linked to aggression and dominance behavior.
Variously, dopamine has been associated with a lot of different behaviors, and is involved in many other different pathways in our noggins. When we talk about it, in general, we tend to refer to the neurotransmitter’s involvement in the feelings of love, lust, and addiction, but along with other chemicals in our brain, it might also relate to our sociality and propensity towards monogamy.
This particular finding is therefore interesting because it matches up with earlier genetic studies, which have found that the activity of the genes that code for the enzymes that make dopamine is far higher in humans than in apes. Even more significantly, this activity was also seen in the same region of the brain in which the latest study also found elevated levels of the neurotransmitter.
Quite boldly, the authors of this paper argue that it may have been these underlying differences in brain chemistry that set in motion our increase in intelligence, evolution of language, and even eventually the development of tools.
In what they call the “neurochemical hypothesis for the origin of hominids”, they suggest that early female hominins were choosing to mate with males that were more outgoing, but at the same time less aggressive than the others, while males who were cooperating and hunting with other males were also likely to be more successful.
As the cooperation between differing individuals developed and deepened, they would have likely shared knowledge and tool-making skills. Finally, the authors propose, these early hominins would have developed language, which in turn would have sped up the creation and spread of new technologies. And all this because of a feedback loop created by dopamine, or so they say.
Clearly, in reality, it is impossible to prove whether this is what happened or not. And as stated before, the role of dopamine in the human brain is incredibly varied, meaning that pinning it down as the cause of social changes in the behavior of a species hundreds of thousands – millions even – of years ago is quite shaky really. Either way, it is an interesting new take on our origins.