© Hanna Knutsson, 2017, Flickr Photo Album, some rights reserved.
Rethinking Cognitive Function
Recently, the scientific community has become more enthusiastic about the study of how cognitive ability, or the capacity to perform higher mental processes, may affect a non-human animal’s ability to successfully pass on its genes. Scientists are now researching and reporting interesting studies relating to cognition: non-human animals invest resources into building tissue needed for cognitive function (like the brain), have very complex displays during courtship rituals, and exhibit cognitive abilities far beyond what we gave them credit for in the past.
This recent work has had interesting implications in the world of animal behavior: scientists are thinking of cognitive processes and their relationship with sexual selection more than ever before. One interesting hypothesis put forth aims to explain how intelligence affects reproductive success. This hypothesis posits that a positive relationship exists between an animal’s cognitive ability and its ability to reproduce and pass on its genes; in other words, it asserts that smart is sexy.
Smart Dad = Smart Kids
So, why would smart be sexy? Thinking of this in a context where a female is choosing between many males to mate with, we can consider many explanations. The first has to do with what the female in our situation is looking for in her offspring. Assuming that the gene for smarts is heritable, or able to be passed down genetically through generations, then there may be an advantage for the female to mate with a smart male for the good genes that he can pass down to her offspring. Just think – if the female were to mate with an especially smart male and her offspring were to inherit certain traits for intelligence, then there would be great benefits for both her sons and her daughters.
Sons may have the same cognitive abilities as dad, allowing them to be successful in mating later in life so as to continue passing on the family genes. Similarly, daughters may be better at discerning who the smart males are; and thus, will be able to repeat the process of conferring smart genes to future offspring. To top it off, both sons and daughters would have some outstanding general benefits from genes for higher cognitive performance. They may be able to better avoid predators, be better learners, or be better decision-makers. It seems difficult to argue with that logic!
Putting the Hypothesis to the Test
The cognitive performance hypothesis had not been the subject of direct experimental study until recently, when a team of scientists decided to test this hypothesis in a population of satin bowerbirds (Ptilonorhynchus violaceus).
Satin bowerbirds are medium-sized birds that inhabit the wet forests and woodlands of eastern to southeastern Australia. They are a visually striking species: males sport glossy black plumage and females flash olive-green backs with beautifully scalloped underparts. Both sexes also have striking blue irises. What might be most remarkable about the satin bowerbird, however, is the male’s courtship ritual. Male satin bowerbirds, like other species in the family, build amazing “theaters” (called bowers) to use in their displays for females. Satin bowerbirds bowers consist of a narrow, U-shaped arrangement of sticks called an “avenue” and a careful assortment of blue objects. During the male’s display, the female watches from the avenue while the male struts and moves in a routine while holding up various objects.
This experiment used the satin bowerbird’s love for blue objects, and strong aversion to red objects, as a window through which to test the birds’ problem solving abilities. The researchers devilishly placed red objects in the center of the satin bowerbird’s court to see how long it took for them to be removed.
The series of experiments advanced in difficulty, and by the end of the trials the bowerbirds were forced to devise a way to hide an intrusive red object nailed to the ground in the middle of their court area. By measuring each male’s performance, and relating that to his mating success, the scientists tested the cognitive performance hypothesis. And the results? The team of researchers found that mating success was correlated with a male’s performance on the problem-solving tests; in other words, the smarter males were experiencing more mating success too.
A different team of researchers sought to test whether cognitive ability could manifest itself physically on an individual, so as to allow other individuals to gauge how smart you are based on looks alone. To test this, they used the carotenoid-derived stripe on siskins to see whether males who are better able to solve foraging problems have bigger carotenoid stripes on their wings.
The siskin is a small finch with a yellow stripe on its wings. This yellow stripe is special in the sense that it derives its color from carotenoids, or pigments that give some feathers a red to yellow color. Females prefer males with longer carotenoid stripes, therefore the stripe has direct impacts on mating success.
In a cleverly-designed experiment, the researchers simply presented different male siskins with a feeder which required a puzzle to be solved to obtain food. They recorded the size of the stripe on the Siskin solving the problem, as well as the time it took him to do it.
The result? The male siskins who solved the problem more quickly (and thus had greater cognitive abilities) also had larger carotenoid stripes! This shows that cognitive ability can be signaled through an aspect of physical appearance, such as the length of a stripe; and since the length of the stripe is related to mating success, we see again that cognitive ability is playing a role in mate choice.
So what do the results of cognitive ability’s relationship with mating success mean in the animal world? For one, these studies have opened the door to testing an interesting hypothesis, as the relationship between cognitive ability and mating success remains a viable area for future research. These studies also serve as a fascinating example of a system in which smarter males appear to have greater reproductive success than their lower-performing comrades.
So, is smart really that sexy? Well, it appears that it’s up to nature to decide.
- Animal Behaviour – Male satin bowerbird problem-solving ability predicts mating success
- Biology Letters – Sexy birds are superior at solving a foraging problem
- Behavioral Ecology and Sociobiology – Female siskins choose mates by the size of the yellow wing stripe