The evolution of animal personalities - they're a fact of life


Blogging on Peer-Reviewed ResearchAnimals have distinct personalities and temperaments, but why would evolution favour these over more flexible and adaptible mindsets? New game theory models show that animal personalities are a natural progression from the choices they make over how to live and reproduce.

Any pet owner, wildlife photographer or zookeeper will tell you that animals have distinct personalities. Some are aggressive, others are docile; some are bold, others are timid.

An animal's reproductive decisions can determine if it is a hawk...In some circles, ascribing personalities to animals is still a cardinal sin of biology and warrants being branded with a scarlet A (for anthropomorphism). Nonetheless, scientists have consistently found evidence of personality traits in species as closely related to us as chimpanzees, and as distant as squid, ants and spiders.

These traits may exist, but they pose an evolutionary puzzle because consistent behaviour is not always a good thing. The consistently bold animal could well become a meal if it stands up to the wrong predator, or seriously injured if it confronts a stronger rival. The ideal animal is a flexible one that can continuously adjust its behaviour in the face of new situations.

And yet, not only do personality types exist but certain traits are related across the entire animal kingdom. Aggression and boldness toward predators are part of a general 'risk-taking' personality that scientists have found in fish, birds and mammals.

Max Wolf and colleagues from The University of Groningen, Netherlands, have found a way to explain this discrepancy. Using game theory models, they have shown that personalities arise because of the way animals live their lives and decide when to reproduce.

For an animal, success is measured achieved through living long enough to reproduce, and individuals constantly gamble their current success against their future one. They could reproduce now, or defer it to a later time when resources are more abundant.

The crux of Wolf's theory is that those with a stable, assured future have more to lose by gambling, and are likely to be more risk-averse. Those with little to lose can afford to live fast and die young.

Wolf tested this idea by using a mathematical model to simulate these choices and their consequences. The protagonist of his model is a fictional animal that lives in an area with many territories, some rich in food and others lacking it.

The animal can choose how thoroughly it wants to explore its habitat. If it is adventurous, it could find a lush and bountiful territory, but it will have less energy to raise young, and must postpone this to the following year. That may not be so bad - its new home will give it a ripe, long life and it will have many opportunities for breeding.

or a dove.He found that simulated animals picked one of two stable strategies. Some decided to explore thoroughly and hope for greater reproductive success in the future. Others decided to stay put, have young now and make the best of things, poor resources be damned.

Wolf then modelled how these two groups would react to decisions about risk, in a classic hawk-dove experiment. When faced with a predator or a rival, the animal could run away or back down (dove), which takes time and could lose it feeding opportunities or its territory. If it stood and fight (hawk), the likelihood of death or injury was greater but so were the rewards.

Sure enough, the explorers who were investing on future success, consistently evolved to be docile, timid and risk-averse, while those who reproduced immediately consistently became bold and aggressive. These patterns held up under a wide range of simulated conditions. Over time, they gave rise to stable individual differences and behaviour traits that were consistently linked with each other, the foundations of personality.

In New Scientist's coverage of this story, Judy Stamp from the University of California, Davis, criticises Wolf's work for only explaining extremes of personality. Obviously, animals are not always black hawks or white doves, but many shades in-between.

But Wolf's study answers this too. In the most advanced version of his model, he accounted for the fact that behaviours are governed by many heritable genes. This generated a much more realistic and continuous spectrum of personalities. Even with this more plausible model, the same principle applied - the more an animal had to lose, the fewer risks it was prepared to take.

Wolf is now keen to see his theory tested in the field. He suggests that many other behaviour traits could be linked to aggression or boldness. Individuals that invest heavily in the present may be more likely to guard nests, care for their young or woo mates with conspicuous and costly displays.

Reference: Wolf, van Doorn, Leimar & Weissing. 2007. Life-history trade-offs favour the evolution of animal personalities. Nature 447: 581-584.

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Cool. There was some work done comparing behaviors of mountain lions in the Northwest to their desert dwelling cousins in the Southwest that showed aggressiveness/territorial behavior in the low (SW) populations.

And for further study I offer Felis Sylvestris Catus, or the common household cat.

All the same equipment as other Felids, but adoption of a more docile, kitten-like behavior.

Then of course there are the Russians who bred more docile foxes and ended up with foxes that behaved more like dogs than foxes.

Sharks also have distinctive personalities. One that I rescued from a loose hook recognized me and treated me differently than the other humans it encountered while it recuperated from its injuries in our shark pond. Other sharks I've held in captivity temporarily have been quite hostile towards me. The behaviors are consistent for an individual but vary greatly between individuals.

Tony in his post above, mentions behavior but there were also significant physical traits that were expressed as well. It's been suggested that genetically controlled behavioural traits, such as late-onset of certain instinctive behavior like the expression of dominance and aggression, are associated with physical traits which might also be selected, even if inadvertantly, which never the less could have wide ranging implications.
Might be interesting to see if an experiment similar to the siberian foxes were to be conducted in a controlled population of primates. Would we see more juvenile forms indicated by increased gracility and longer/increased growth for the brain?

Thanks for posting on the personality traits of animals, very interesting.

One thing I've observed is how cats--all cats, whether lions or tigers or feral cats or domestic cats, although they do each have distinct personality traits individually, they as a species have one trait all in common: Pride.

From the old, beaten up scroungy alley cat to the feral who's never experienced human interaction, to the domestic to the large wild cats to the and wild small cats, they all have this "proud lion" aspect about them. A pride that goes way beyond all the other species of animals. In fact, so much pride that they even get "embarassed" when they jump and miss a climb or when laughed at. It's really remarkable. If the average human had as much pride as the cat, it would truly be irritating and obnoxious, but for some reason it is justified and seems good and right in the feline.

The pride of the feline.

Evolution cannot explain it. This goes way beyond an individual animal's personality. And neither adaptation for survival nor even instinct sufficiently can addresses it. The pride of felines. They own it.

I think this is one thing evolution cannot explain.