The continuing evolution of human reproductive behaviour

in the series Evolutionary Demography

Date: Monday 24 April 2017
Time: 5:30 pm - 6:30 pm
Venue: Curtis Room - LG9, LSHTM, Keppel Street, London, WC1E 7HT, UK
Type of event: Seminar
Speaker(s): Lesley Newson, University of California, Davis

Hosted by the School's Evolutionary Demography Group 

Abstract: The first hominin skull to hold a brain larger than the brain of a chimpanzee has been dated to 1.8 million years ago. Isler and van Schaik have argued that provisioning offspring with a brain larger than that of a chimpanzee (adjusted for body size) would be impossible for a mother on her own and so conclude that alloparenting must have begun by this point in human evolutionary history.

Allomaternal care was probably also linked to the evolution of more complex culture. Without it, individuals would not have evolved the capacity to drive the changes that made culture more complex and useful. At the same time, shared culture allowed groups to organize reproductive effort more effectively, sharing out parental and alloparental responsibilities among family members and family allies. The two behaviours co-evolved. 

To be successful, a family group needed to harness its members to cooperate in raising of offspring which were not necessarily their close genetic relatives. Families which were good at acquiring resources and efficiently turning them into new generations of family members thrived at the expense of other families. Successful families shared culture which included a combination of rules, incentives and sanctions that encouraged sufficient cooperation.  Success also depended on family members having genes which made them good at the work and susceptible to cultural harnessing. Natural selection worked on families, selecting both the cultural and the genetic variants that were associated with their success. Hominins changed by a slow process of gene-culture coevolution. 

Modern humans organize reproductive effort in a wide variety of ways, suggesting that there is no optimal way to do it. Rules change depending on changing conditions and in response to internal conflict. Complete stability is impossible because family members would always prefer to give less to the family and receive more from it.  

Changes in human reproductive behaviour and other cultural changes, are often explained in terms of individuals responding to changing conditions. 

I will argue that better explanations will be developed if we appreciate the evolutionary nature of cultural change.

Admission: Free and open to all with no ticket required. Entry is on a first come, first served basis.

Contact: Laura Streeter
Email: Laura.Streeter@lshtm.ac.uk

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