Human babies are more vulnerable than those of other species, leading humans to develop higher degrees of intelligence to care for them. Istock

The helplessness of human babies may explain why we developed a superior intelligence to other animals on the planet, scientists have said. Human intelligence is one of the most puzzling questions in evolution.

While a number of theories have been suggested, scientists do not understand why we developed superior intelligence and cognition, including high social reasoning. To find out, a team of researchers created a new evolutionary model to investigate why human intelligence is so distinctive, compared to that of our closest evolutionary relatives.

"Many previous theories had suggested that humans developed their superior intelligence in response to the harshness of the environment around them, but this fails to explain why other species who lived in these same harsh environments and had far longer to potentially develop intelligence did not. For example, reptiles or insects", lead author Celeste Kidd, from the University of Rochester, told IBTimes UK.

"A unifying theory should explain both why higher order mammals developed intelligence but these other species did not."

Compared to many other species, including mammals, human newborns are particularly helpless and vulnerable. While other animals can stand up after just a few hours of being born, this is not the case for babies.

Published in PNAS, the researchers showed that natural selection for large brains may lead to such premature newborns, which themselves require more intelligence to raise, and thus may select for even larger brains.

Self-reinforcing model

The scientists create an evolutionary model which predicts a strong relationship between parents' intelligence, their babies' needs, and the evolution of cognition in the human species.

On the one hand, the model suggests helpless babies require intelligent parents to take care of them, which explains why humans may have developed large brains and increased cognitive skills.

On the other hand, it describes how babies are helpless because they are born prematurely compared to other animals. Such an early birth is the result of them developing a big head to accommodate a large and intelligent brain – which would prevent them from coming out of their mothers if they stayed longer inside the uterus.

The model thus reveals that there are self-reinforcing dynamics between parents' intelligence and offspring's helplessness, eventually creating a species that is more intelligent than others.

A complement to previous theories

Thanks to this model, the scientists are also able to solve a second puzzle: they show what the evolutionary advantages of having helpless babies can be.

Immature newborns confers them greater intelligence than other species and in particular, a specific type of intelligence called "social reasoning". This means that compared to other animals, humans are able to think about how other people may feel and what they need.

"Our theory is interesting because it complements previous theories which note that humans have evolved to be especially capable of social reasoning. It is a kind of intelligence that comes in particularly handy when caring for newborns, as it means humans are better able to respond to their needs", Kidd concludes.