Friday, August 13, 2010

The evolution of costly traits: Competing for women can be unhealthy for men

There are human traits that evolved in spite of being survival handicaps. These counterintuitive traits are often called costly traits, or Zahavian traits (in animal signaling contexts), in honor of the evolutionary biologist Amotz Zahavi (Zahavi & Zahavi, 1997). I have written a post about this type of traits, and also an academic article (Kock, 2009). The full references and links to these publications are at the end of this post.

The classic example of costly trait is the peacock’s train, which is used by males to signal health to females. (Figure below from: The male peacock’s train (often incorrectly called “tail”) is a costly trait because it impairs the ability of a male to flee predators. It decreases a male’s survival success, even though it has a positive net effect on the male’s reproductive success (i.e., the number of offspring it generates). It is used in sexual selection; the females find big and brightly colored trains with many eye spots "sexy".

So costly traits exist in many species, including the human species, but we have not identified them all yet. The implication for human diet and lifestyle choices is that our ancestors might have evolved some habits that are bad for human survival, and moved away from others that are good for survival. And I am not only talking about survival among modern humans; I am talking about survival among our human ancestors too.

The simple reason for the existence of costly traits in humans is that evolution tends to maximize reproductive success, not survival, and that applies to all species. (Inclusive fitness theory goes a step further, placing the gene at the center of the selection process, but this is a topic for another post.) If that were not the case, rodent species, as well as other species that specialize in fast reproduction within relatively short life spans, would never have evolved.

Here is an interesting piece of news about research done at the University of Michigan. (I have met the lead researcher, Dan Kruger, a couple of times at HBES conferences. My impression is that his research is solid.) The research illustrates the evolution of costly traits, from a different angle. The researchers argue, based on the results of their investigation, that competing for a woman’s attention is generally bad for a man’s health!

Very romantic ...


Kock, N. (2009). The evolution of costly traits through selection and the importance of oral speech in e-collaboration. Electronic Markets, 19(4), 221-232.

Zahavi, A. & Zahavi, A. (1997). The Handicap Principle: A missing piece of Darwin’s puzzle. Oxford, England: Oxford University Press.


LeonRover said...

I noted that "Kruger says one way of lengthening the lives of men is to promote a more monogamist and more financially egalitarian society."

When I was introduced to reading about Ev Psych via Pinker, and other pop writers like the Ridley evangelists (Matthew and Mark), my big take was that humans can CHEAT, and cheaters can often have short term success. This applies to reproductive success also, more particularly to men than women, tho' the rates of known cuckoldry has gone up with inexpensive DNA testing. Insofar as cheating behaviour has some genetic component and is not entire a cultural phenomenon it will not die out. So I feel that Kruger's comment comes from the non-science of Sociology 101 and not from the work of decision researchers in Santa Fe and elsewhere.

Byron said...

Hi Ned,
competiton may cause some harms but with victory comes huge advantages. As already known married men are healthier than men who were never married or whose marriages ended in divorce or widowhood. Not because of good cooking I guess. Old suspect "stress relief" factors seems more reasonable. Seems to outweigh other problems you only have as a couple. Greetings.

Ned Kock said...

Hi Leon.

Yes, the EP field was practically founded on cheating research, with the work of Tooby and Cosmides. These are the "parents" of the field of EP, although they don't do much popular writing like Pinker. Pinker's main interest is language.

In fact, many EP researchers think that cheating and, more broadly, political maneuvering, are the reasons why humans became so smart:

Ned Kock said...

Hi Byron.

Until the children become teenagers. That is one stage where major patience tests present themselves.

Unknown said...

This is my first time i visit here. I found so many interesting stuff in your blog especially its discussion. From the tons of comments on your articles, I guess I am not the only one having all the enjoyment here! keep up the good work.
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Ned Kock said...

Hi Rinkesh, thanks.

Helen said...

I think humans are unusual among animals because general longevity (beyond reproduction) helps the group survive, particularly vis a vis child-rearing, food gathering, and the transmission of culture - our most important adaptive trait. This is termed the "grandmother effect." The benefits of having elders in the group may influence genetically determined behavior regarding mating and other factors involved in group/offspring survival.

This theory has also been applied to why having a gay uncle may be beneficial, and why gay uncles have been selected for. Gay uncles (historically childless) tend to invest resources in their nieces and nephews. Really!

Ned Kock said...

Hi Helen, thanks. Yes, evolution is not as simple as many people think, especially in regards to humans.

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