I have broad interests in behavioural and evolutionary biology, but my current research centres on four main topics:

1. Evolution of decision mechanisms

Animals, including humans, do not always behave in the ways predicted by simple optimality models: sometimes they appear to do 'irrational' things. To understand this better, we need to develop a more comprehensive theory of decision making which takes into account the evolved mechanisms underlying behaviour. In a new ERC-funded project at Bristol, we are using novel theoretical approaches to try to explain puzzling features of behaviour such as impulsiveness, intransitivity and state-dependent valuation and understand the evolutionary basis of psychological states.

Collaborators: Luc-Alain Giraldeau, Steven Hamblin, Andy Higginson, Alasdair Houston, Dave MallpressJohn McNamara, Pete Trimmer

2. Flexible mate choice

Sexual selection is a potent evolutionary force, generating an incredible diversity of courtship displays which serve to attract the opposite sex. According to standard 'textbook' theory, all individuals should strongly prefer mates offering high-quality genes or plentiful resources, because this gives them the greatest fitness. This view is at odds with the considerable variation in mate preferences we see in real animals: some individuals have strong preferences, some have weak preferences, and some prefer a different type of mate altogether. We have been building evolutionary models to try and understand why such differences exist. Rather than fixed, uniform preferences, our work suggests that mate preferences should be flexible, with individuals adjusting their choosiness according to their current condition and circumstances relative to others in the population. We have been testing the specific predictions of our models by studying humans taking part in a 'speed-dating' event.

Collaborators: Colin Bleay, Bram Buunk, Rufus Johnstone, Ani Kazem, Jessica Pass, Katharina Riebel

3. Flexible aggression

Just as for mate preferences (see above), there are good reasons why individuals should adjust their levels of aggression depending on their current state. We have been building evolutionary models of flexible aggression in which individuals learn about their fighting strength from the outcomes of previous contests. This has interesting consequences for the way that aggressive behaviour should change with age, and in response to previous experiences of victory and defeat. In parallel work, we have been examining developmental trajectories of aggression in boys growing up in the Canadian province of Quebec, and winner and loser effects in fallow deer during the annual rut.

Collaborators: Dómhnall Jennings, Rufus Johnstone, Richard Tremblay

4. Sex ratios and sexual selection

It is often argued that attractive males should produce more sons, because these sons will inherit their father’s attractiveness. Numerous field and laboratory studies have addressed this hypothesis, but the results are mixed. We have been developing new theory to understand the evolution of sex-ratio adjustment and how this might interact with processes of sexual selection. Alongside, we have been conducting large-scale aviary experiments on zebra finches to determine how sex ratios and maternal investment are affected by the relative attractiveness of the parents, and analysing large datasets of humans in Rwanda to investigate patterns of sex-ratio bias in relation to wife rank.

Collaborators: Bram Kuijper, Ido Pen, Thomas Pollet, Nikolaus von Engelhardt, Franjo Weissing, Klaudia Witte, Richard Zann