Michael Jennions

senior fellow
EURIAS cohort 2016/2017
discipline Biology
Professor of Evolution, Ecology & Genetics, The Australian National University

Research project

Causes and Implications of Adult Sex Ratio Variation in Vertebrates


Although enormous cultural differences in gender roles exist, some universal truths seem to exist. For example, in every human society it is women that disproportionately provide child care; and far more young men than women are imprisoned for violent crimes. Why? For biologists the situation is still more challenging as animal species vary hugely: in seahorses males become "pregnant"; in some species parental care is only provided by males, in others by females and in others care is biparental. Why these differences in sex roles? Preliminary work suggests the adult sex ratio (ASR) might explain some variation among human societies (which is potentially important given sex-biased abortion and/or youth mortality).


At Wiko Berlin this work is going to be extended to fish and frogs to test the generality of these predictions; and to collaborate with anthropologist to refine the predictions. My main goals are to:


(i) Collect data on ASR from amphibian and fish species to predict variation in sex roles. Both taxa are unusual (compared to other major taxa) because they do not show the familiar pattern of female-biased parental care.


(ii) Take advantage of the opportunity for close collaborations with Tamas Szekely to learn comparative phylogenetic methods. In addition there is potential to formalise the extent to which meta-analyses that incorporate the lack of statistical independence between effect sizes due to species relatedness are equivalent to comparative analyses that weight the data by the confidence with which the traits of interest have been estimated.


(iii) Use the fact that other focus group members will be conducting similar analyses but for other taxa to develop common solutions to issues surrounding data collection (e.g. one sex might be easier to catch than the other).


(iv) Take advantage of my own "talent" at writing reviews to collaborate with colleagues working on humans to identify shared problems and conceptual issues. Most (probably all) of the variation in mating systems, levels of violence, mate choice among human populations is due to phenotypic plasticity. However, the ASR models to predict sex roles are evolutionary models. Consequently it is important to think carefully about the extent to which we expect evolutionary responses predicted by the model to be mirrored as shorter-term plastic changes in investment by each sex in parental care and/or sexual competitiveness in humans. Evolutionary biology has much to teach us about human behaviour, but models should not be naïvely applied.




Michael Jennions is Professor of Evolution, Ecology & Genetics at the Research School of Biology of the Australian National University. He holds a Ph.D in Zoology from the University of Oxford. He has special interest in behavioural ecology. His works are mainly on sexual selection and reproductive decisions (female choice, male-male competition, sperm competition, parental care, life histories etc).


Selected publications


'Coevolution of Parental Investment and Sexually Selected Traits Drives Sex-Role Divergence', with L. Fromhage, Nature Communications, vol. 7, 2016, article 1517.


'Local Gamete Competition Explains Sex Allocation and Fertilization Strategies in the Sea', with J.M. Henshaw, D.J. Marshall & H. Kokko, The American Naturalist, vol. 184, no. 2, 2014, pp. E32-E49.


'Penis Size Interacts with Body Shape and Height to Influence Male Attractiveness', with B.S. Mautz, B.B.M. Wong & R.A. Peters, Proceedings of the National Academy of Sciences, vol. 110, no. 17, 2013, pp. 6925-6930.


'Adaptive Sex Allocation in Anticipation of Changes in Offspring Mating Opportunities', with A.T. Kahn & H. Kokko, Nature Communications, vol. 4, 2013, pp. 1603.


'Unifying Cornerstones of Sexual Selection: Operational Sex Ratio, Bateman Gradient and the Scope for Competitive Investment', with H. Kokko & H. Klug, Ecology Letters, vol. 15, no. 11, 2012, pp. 1340-1351.



junior fellow
EURIAS promotion 2016/2017
Wissenschaftskolleg zu Berlin
discipline Music
senior fellow
EURIAS promotion 2013/2014
Wissenschaftskolleg zu Berlin
discipline Sociology
junior fellow
EURIAS promotion 2016/2017
Wissenschaftskolleg zu Berlin
Social Sciences
senior fellow
EURIAS promotion 2015/2016
Wissenschaftskolleg zu Berlin
discipline History