Animals differ strikingly in character and temperament. Yet only recently has it become evident that personalities are a widespread phenomenon in the animal kingdom. Animals as diverse as spiders, mice and squids appear to have personalities. Personality differences have been described in more than 60 species, including primates, rodents, birds, fish, insects and mollusks.
New work by Max Wolf (University of Groningen; currently at the Santa Fe Institute), Santa Fe Institute Postdoctoral Fellow Sander van Doorn, Franz Weissing (University of Groningen), and Olof Leimar (Stockholm University) offers an explanation for the evolution of animal personalities.
The evolutionary origins of "animal personality"--defined as consistent behavior over time and in different situations--is poorly understood. Why do different personality types exist within a single population given that, at first sight, one would expect one type to be more successful than another? Why are individuals not more flexible considering that personality rigidity sometimes leads to seemingly inefficient behavior? Why do we find the same types of traits correlated with each other in very different kinds of animals?
The authors argue that in many cases personalities are shaped by a simple underlying principle: the more an individual stands to lose (in terms of future reproduction) the more cautiously it is likely to behave, in all kinds of situations and consistently over time.
They begin with two basic observations. First, variation in personalities is often structured according to differences in the overall willingness to take risks. Second, individuals are often confronted with a trade-off between current and future reproduction: the more an individual currently invests in reproduction, the less resources are left to invest in future opportunities, and vice versa.
Using a mathematical model the authors demonstrate that this fundamental trade-off can give rise to populations where some individuals put more emphasis on future reproduction than others. Individuals who invest in future reproductive success evolve to be consistently risk-averse in different behavioral contexts (e.g. encounters with predators and aggressive interactions), whereas individuals who put emphasis on current reproductive success evolve a more risk-prone personality.
The researchers intend to continue their collaborative work on the evolution of animal personalities. Currently, at the Santa Fe Institute, Max Wolf and Sander van Doorn are developing alternative ideas on structuring properties of personalities.
These findings are detailed in "Life-history trade-offs favour the evolution of animal personalities" in the May 31 issue of Nature.
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