Replying to: R. McElreath, B. Luttbeg, S. P. Fogarty, T. Brodin & A. Sih Nature 450, doi: 10.1038/nature06326 (2007)

The evolution of animal personalities is still poorly understood. The emergence of consistent individual differences is relatively easy to envisage when initial differences in behaviour are reinforced by positive feedback mechanisms. Such reinforcement might act through learning or training, or through behaviour-induced changes in an individual's condition¹ or environment². However, positive feedback is not required. We showed that, even without such feedback, differences in fitness expectations result in consistent differences in risk-taking behaviour³. This was illustrated by a model that, for simplicity, considers a short life history. McElreath et al. ⁴ argue that our results extend to long-lived organisms only under specific conditions. Although we agree that the full scope and limitations of our model still have to be mapped out, we believe that our arguments are also relevant to long-lived organisms.

1. Theoretical Biology Group, Centre for Ecological and Evolutionary Studies, University of Groningen, Kerklaan 30, 9751 NN Haren, The Netherlands
2. Santa Fe Institute, 1399 Hyde Park Road, Santa Fe, New Mexico 87501, USA
3. Department of Zoology, Stockholm University, SE-106 91 Stockholm, Sweden.
   Email: f.j.weissing@rug.nl

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