The unique life history of humans

If an Alpha Centauran biologist came to Earth during the Pleistocene and tried to figure out what makes the new branch of primates different from existing primates, what might she notice? Professor Alison Gopnik, of the University of California at Berkeley, thinks it is their 'life history' that would have stood out. In evolutionary biology, life history is the developmental programme of an organism across its life.

The life history of humans is radically different from our closest relatives, Gopnik said. We have a very long period of immaturity and dependence in childhood, as well as a long period of vulnerability and dependence in older age. These periods of dependence are very costly, and seem counterintuitive from an evolutionary perspective. But Gopnik argued that humans have adapted for this with what she calls the 'investment triple threat'. 

First there is pair bonding between the parents who cooperate to raise children together – which is very rare in mammals. Then there are alloparents, who are not biologically related but care for children. And finally there are grandmothers (Gopnik's favourite – she showed a picture of her three grandchildren) who are a strikingly human phenomenon. The 'grandmother hypothesis' is that postmenopausal women enabled the protracted period of human childhood. Parents, who are in the prime of life, forage, mate and acquire resources, while grandparents, who are less effective at those things, pass on information and ensure children survive. 

Gopnik said that the extended period of protected childhood allows children to explore and learn about the world in a safe environment. In adulthood, there is a shift to a goal-directed 'exploitation' cognitive profile, which allows us to get things done based on what we've learnt. Gopnik described what is known in computer science as a trade-off between exploration and exploitation. The intrinsic tension between the two means that in adulthood it is challenging to switch between explore and exploit.

This explore-exploit trade-off is even relevant to academia. Gopnik said that when she did her DPhil it was considered a time to explore, rather than to exploit (i.e. publish). It seems that the life history of an academic is evolving to include just a short period of exploration followed by a long period of goal-directed exploitation. Nonetheless, Gopnik did encourage students to be exploratory – sometimes this leads to the most successful work. 

These ideas are discussed in much more detail in Gopnik's recently co-edited special issue of Philosophical Transactions of the Royal Society on life history and learning.