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If we somehow remove pheromones, do animals experience a phenomenon similar to human "visual beauty" when looking at members of the opposite sex? For example, given a set of 20 female ducks observed through a glass panel, would male ducks attempt to court/mate with a small subset of female ducks first(more attractive ones), or is it based on some other criteria (most receptive, random, closest, fittest, pheromones, etc?)

If there is some "visual attractiveness selection criteria", is there a requirement of certain complexity of the brain and/or visual system for an animal before this phenomenon starts to occur?

I'm aware of the existence of this question: Why does sexual selection evolve beautiful features?, and my question deals with the members of the same generation, not long-term evolution.

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up vote 7 down vote accepted

There are numerous examples of visual attraction in animals. An absolute classic of an experiment, taught to most/all evolutionary biology students, is the widowbird tail length experiment by Andersson. He experimentally manipulated the tail lengths of male widowbirds at random. Some tails were made longer and some shorter. From this experiment Andersson showed that females choose males with longer tails more preferentially. Another classic example is the lek mating system where there is a bias in reproductive success towards attractive males, in some cases 10-20% of the males get 70-80% of the matings.

A lek is an aggregation of males that gather to engage in competitive displays that may entice visiting females who are surveying prospective partners for copulation. Leks are commonly formed before or during the breeding season. A lekking species is defined by the following characteristics: male displays, strong female mate choice, and the conferring of male indirect benefits. Although lekking is most prevalent among avian species, lekking behavior is found in a variety of animals such as insects, amphibians, and mammals

Beauty could be a an example of a an indicator trait:

Indicator traits are those that signal good overall quality of the individual. Traits that are perceived as attractive must reliably indicate broad genetic quality in order for selection to favor them and for preference to evolve.

I'm sure there are some studies in fish, likely guppies or zebra fish, which gave individual fish the opportunity to visually assess potential mates (placing tanks next to each other and observing courtship) which would be very similar to your hypothetical duck example. Despite often being a paradox, female mate choice is well documented. Further, male mate choice is now coming to light, even in species where female mate choice and male-male competition exists.

I don't think selection on "beauty" would require some kind of particularly special neural system, obviously some visual capacity is necessary for visual attraction and some basic neural pathways linked to that. I have done experiments myself in Drosophila simulans which looked at good gene benefits of mating with attractive males (indirect genetic benefits of female mate choice) and another which assessed precopulatory selection (female mate choice) for a secondary sexual character in the same species. Even in such a small-brained species there appears to be some degree of (partially visual) mate choice going on.

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Those articles mention 2 examples of bird visual preference: a) better diet translates into more plumage pigment in some birds b) parasites dull the color of certain parts of plumage – Alex Stone Oct 24 '14 at 1:29
@AlexStone Thanks, could you please include a citation on that quote you've edited in – rg255 Oct 24 '14 at 7:21
I added the link – Alex Stone Oct 24 '14 at 17:10

Absolutely. Quality by appearance is sometimes a big part of mate selection and sometimes it is not.

The size and cognitive capacity brain is probably important but not always. Primates are closest to us and have most similar tastes to us, have varying levels of interest in mate appearance. Most primates have a troupe dominance where a dominant male mates with all the females and sires as many offspring as he can before he loses his place on top. Many smaller primates rely more on sperm competition and the females mate with all the males they can when they are in estrus - the offspring just emerge from the most competitive sperm. Note I studied Sarah Hrdy a while ago. I hear Robert Sapolsky is another great source of insight on primate/human behavior.

Neither of these modes are quite so focused on visual beauty as our culture is. Other cultures are also not selective based on appearance, e.g. cultures where marriages are arranged would often consider the social and economic relationships between the families more than we do. This is a broad generalization, but just to point out that just looking at someone to decide mate choice isn't as dominant as sometimes it feels.

But to look at some tiny brains I know that snakes often mate in gigantic balls of snake and mate choice is pretty indiscriminate, on the other hand, spiders where female choice is dominant, males will experience rejection. This is a bummer for the males because they only often live long enough to offer to one mate. Its probable that the females are not hungry or have recently mated with another male, but just an example to demonstrate that even small brained animals can be discriminating.

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It would be interesting to know if an alpha primate male, while mating with all his females still shows stronger preference to some of them, and if so, what controls that attraction – Alex Stone Aug 1 '13 at 12:29
Good observation. There are definitely favorites amongst primates (i mean besides humans, who obviously play favorites). Hrdy and Sapolsky's books have examples where females in the troupe are definitely favored recipients of mating behavior - younger females have an easier time producing offspring and so are favored just as they are with humans for instance. There are also observations that female apes will break away from the alpha male for males who treat them better. – shigeta Aug 1 '13 at 14:53

In addition to the answers stated here, it is also important to remember that we, humans, are more guided by vision than many other animals. Therefore, the idea of separating an animal from a potential mate with glass would also inhibit other important mate selection criteria that other organisms use (calls, pheromones, nest tending, etc.).

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You seem to be dissociating physical beauty from fitness. In fact, beauty can be taken as a measure of biological fitness. For a classic, if simplistic example, many male humans find large breasts attractive and beautiful, however, large mammary glands are also an indication of fertility and robustness that would imply the prospective mate would be a good mother.

Anything that we consider beautiful in a prospective mate can be interpreted in terms of fitness. Another classic example is symmetry. Humans are attracted to symmetrical faces and bodies. Since we are a symmetrical species, symmetry is an indication of fitness. In other words, lack of symmetry may indicate a developmental problem and by extension decreased fitness.

There isn't really a qualitative difference between the way we define attraction and the way other animals do. In both cases we have instinctive attractions to healthy and fit (in the evolutionary sense) mates. It is simply that our complex society has marked these choices as "aesthetics" while we call them "instincts" in other animals.

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Since asking this question, I've learned that 97% of male mammals do not have concept of "beauty" and will mate with every female indiscriminately. These species do not have any paternal investment, so the males are not picky.

In other 3% of mammals (~100 species) and a lot of birds, there is a significant degree of paternal investment in offspring. Species that have developed a "pair bond" mating strategy, have males capable of perceiving "beauty" in females and become much more picky. Humans are a pair bond species.

On the other hand, because mammal females have high investment in their offspring, without the pair bond females go straight for the top alpha male to secure his DNA.

The 97% -3% number is quoted multiple times in this podcast on Evolutionary Psychology:

There's also this article on social monogamy in mammals that quotes 3-5% figure

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Can you provide a reference to the numbers you refer to? – fileunderwater Apr 27 at 14:33
@fileunderwater I have added a couple links – Alex Stone Apr 27 at 14:36

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