The wild life of female promiscuity and the evolution of family living

A mystery of evolution – that is, why animals cooperate when cheating helps the fittest survive – is being addressed thanks to new wildlife funding that could explain the origins of family living.

Mr Tom Botterill-James from the University of Tasmania’s School of Biological Sciences, is investigating how female promiscuity and a changing environment influences conflict in families of lizards. And his results may extend to other species.

‘A key question in evolutionary biology is that if the strongest survive through the selection of the fittest genes, why do animals cooperate?’ said Mr Botterill-James. ‘There should be greater benefits to cheating the system.’

To understand what drives animals to cooperate, Mr Botterill-James is studying White’s skink lizards. ‘These skinks are unique in that that they are one of few lizard species that live as a family of a mum, dad and kids, so we can get insights into the origins of why family living is preferred over a solitary lifestyle,’ he said.

Mr Botterill-James is one of around 100 students to share in more than $1 million in funds from the Holsworth Wildlife Research Endowment, announced today by the Ecological Society of Australia. His research will focus on how promiscuity of females, and changing availability of environmental resources such as food, affect the levels of cooperation versus conflict between partners, parents and their offspring, and between siblings. 

‘If females mate with different males it turns biological fathers into non-biological fathers, and full siblings into half siblings, which should decrease the benefits to siblings of cooperating with one another and decrease the benefits to fathers of investing in those offspring. In turn, this should lead to more conflict between family members and lower the chances of the family staying together.’

He has experimentally manipulated relationships by catching lizards, having different females mate with one or more males in a laboratory setting, and filmed them to find that female promiscuity increases aggression between family members. 

‘Next I’ll see how these lab results play out in nature. I’ll take genetic samples in wild populations to estimate relationships, observe family groups, and see if female promiscuity is a barrier to families, and if monogamy promotes family living.’

He said helping family members, who share genes with relatives, helps the survival of their genetic material. ‘I hope to use these unique family-living lizards to boil down the basis of the evolution of family life, and find the initial triggers for the evolution of family living.’

Dr Bill Holsworth has supported more than 830 students since establishing the Holsworth Wildlife Research Endowment with his wife Carol in 1989. The fund is now managed through a partnership with the Ecological Society of Australia. More information about the Holsworth Wildlife Research Endowment is available at