The study by academics from UCL, University of Manchester, University of Oxford and University of Auckland, is the first to reveal this evolutionary pathway for the emergence of pair living.
The team also found that following the emergence of monogamy males are more likely to care for their offspring. Where fathers care for young, not only can they protect infants from other males, but they can also share the burden of childcare.
Dr Kit Opie (UCL Anthropology), lead author of the study published in the journal PNAS, said: “This is the first time that the theories for the evolution of monogamy have been systematically tested, conclusively showing that infanticide is the driver of monogamy. This brings to a close the long running debate about the origin of monogamy in primates.”
Infants are most vulnerable when they are fully dependent on their mother because females delay further conception while nursing slowly developing young. This leads to the threat from unrelated males, who can bring the next conception forward by killing the infant. Sharing the costs of raising young both shortens the period of infant dependency and can allow females to reproduce more quickly.
An additional benefit of sharing the burden of care is that females can then have more costly young. The considerable cognitive requirements of living in complex societies has resulted in many primate species having large, and costly, brains.
Growing a big brain is expensive and requires that offspring mature slowly. Caring fathers can help alleviate the burden of looking after young with long childhoods and may explain how large brains could evolve in humans. Humans, uniquely among primates, have both very long childhoods and mothers that can reproduce quickly relative to other great apes.
Until now, a number of hypotheses have been proposed to explain the evolution of monogamy among mammals. These include:
• Paternal care, when the cost of raising offspring is high
• Guarding solitary females from rival males
• Infanticide risk, where males can provide protection against rival males
To uncover the evolutionary pathway the team gathered data across 230 primate species. These were then plotted on a family tree of the relationships between those species. Bayesian methods were used to re-run evolution millions of times across the family tree to discover whether different behaviours evolved together across time, and if so, which behaviour evolved first.
This then allowed the team to determine the timing of trait evolution and show that male infanticide is the cause of the switch from a multi-male mating system to monogamy in primates, while bi-parental care and solitary ranging by females are a result of monogamy, not the cause.
Dr Susanne Shultz, from The University of Manchester, said: “What makes this study so exciting is that it allows us to peer back into our evolutionary past to understand the factors that were important in making us human. Once fathers decide to stick around and care for young, mothers can then change their reproductive decisions and have more, brainy offspring.”
Notes for editors
1. To interview Dr Susanne Shultz, from The University of Manchester, please contact Alison Barbuti | Media Relations Officer | Faculty of Medical and Human Sciences |The University of Manchester | Manchester Academic Health Sciences Centre (MAHSC)
Tel. +44 (0)161 275 8383 Internal: 58383 | Mobile 07887 561 318 |Email: email@example.com
2. For more information or to speak to Dr Kit Opie, please contact George Wigmore in the UCL Media Relations office on tel: +44 (0)20 3108 9195 or email: firstname.lastname@example.org
3. ‘Male infanticide leads to social monogamy in primates’ by Opie at al. is published in PNAS. Copies are available from UCL Media Relations.
About UCL (University College London)
Founded in 1826, UCL was the first English university established after Oxford and Cambridge, the first to admit students regardless of race, class, religion or gender and the first to provide systematic teaching of law, architecture and medicine.
We are among the world’s top universities, as reflected by our performance in a range of international rankings and tables. According to the Thomson Scientific Citation Index, UCL is the second most highly cited European university and the 15th most highly cited in the world.
UCL has nearly 27,000 students from 150 countries and more than 9,000 employees, of whom one third are from outside the UK. The university is based in Bloomsbury in the heart of London, but also has two international campuses – UCL Australia and UCL Qatar. Our annual income is more than £800 million.
www.ucl.ac.uk | Follow us on Twitter @uclnews | Watch our YouTube channel YouTube.com/UCLTV
The University of Manchester
The University of Manchester, a member of the Russell Group, is one of the largest and most popular universities in the UK. It has 20 academic schools and hundreds of specialist research groups undertaking pioneering multi-disciplinary teaching and research of worldwide significance. According to the results of the 2008 Research Assessment Exercise, The University of Manchester is one of the country’s major research institutions, rated third in the UK in terms of ‘research power’. The University has an annual income of £807 million and is ranked 40th in the world and fifth in the UK for the quality of its teaching and impact of its research.
Oxford University’s Medical Sciences Division is one of the largest biomedical research centres in Europe, with over 2,500 people involved in research and more than 2,800 students. The University is rated the best in the world for medicine, and it is home to the UK’s top-ranked medical school.
From the genetic and molecular basis of disease to the latest advances in neuroscience, Oxford is at the forefront of medical research. It has one of the largest clinical trial portfolios in the UK and great expertise in taking discoveries from the lab into the clinic. Partnerships with the local NHS Trusts enable patients to benefit from close links between medical research and healthcare delivery.
A great strength of Oxford medicine is its long-standing network of clinical research units in Asia and Africa, enabling world-leading research on the most pressing global health challenges such as malaria, TB, HIV/AIDS and flu. Oxford is also renowned for its large-scale studies which examine the role of factors such as smoking, alcohol and diet on cancer, heart disease and other conditions.