Is Sexual Selection Theory Up For Grabs?

July 9, 2012

The most important study investigating sexual selection theory has been painstakingly recreated and found to be completely invalid. From Science Daily:

A classic study from more than 60 years ago suggesting that males are more promiscuous and females more choosy in selecting mates may, in fact, be wrong, say life scientists who are the first to repeat the historic experiment using the same methods as the original. 

In 1948, English geneticist Angus John Bateman published a study showing that male fruit flies gain an evolutionary advantage from having multiple mates, while their female counterparts do not. Bateman’s conclusions have informed and influenced an entire sub-field of evolutionary biology for decades.

Bateman’s Principle states that females are choosy because there is little advantage to their mating with multiple males. This is the cornerstone of Darwin’s sexual selection theory. The new study was led by Patricia Adair Gowaty, a distinguished professor of ecology and evolutionary biology at UCLA.

In the original experiment, Bateman isolated equal numbers of male and female fruit flies, and then checked the offspring’s genetic features to see how many males had reproduced. Because they did not have the ability to examine DNA, Bateman used flies with severe genetic mutations instead to see how they would show up in offspring. However, there was a “fatal flaw” in his analysis. Bateman assigned paternity based on flies with double mutations, ignoring the flies with zero or one mutations. Consequently, Bateman was unable to accurately quantify the number of mates for each subject. Oddly, he assigned more offspring to males than females, an impossibility. Bateman concluded:

1) The variation in number of mates for males was greater than for females.

2) The males show direct proportionality between number of mates and fertility… The females, provided they have been mated with at least once, show absolutely no effect of number of mates.

In recreating the experiment with DNA analysis, Gowaty et al found that the data were “decidedly inconclusive.”

Here was a classic paper that has been read by legions of graduate students, any one of whom is competent enough to see this erro. Bateman’s results were believed so wholeheartedly that the paper characterized what is and isn’t worth investigating in the biology of female behavior.

Repeating key studies is a tenet of science, which is why Bateman’s methodology should have been retried as soon as it became important in the 1970s. Those who blindly accept that females are choosy while males are promiscuous might be missing a big piece of the puzzle.

Our worldviews constrain our imaginations. For some people, Bateman’s result was so comforting that it wasn’t worth challenging. I think people just accepted it.

Gowaty believes that women are naturally more promiscuous and less choosy than Darwin originally thought.

“Darwin, and later Bateman, cleaved to the notion that females of a species tended to be discriminating and passive, while the far more promiscuous males competed for their attentions. In the last few decades, however, evolutionary biologists have shown that the story is far more complicated. Gowaty, who has been interested in female mating habits in insects and birds since the beginning of her career, spent 30 years in the field studying Eastern bluebirds. She published the first molecular genetics study showing that females in a socially monogamous species mated outside their traditional pairs regularly.

Gowaty describes the benefits of multiple mates as an answer to the never-ending evolutionary struggle against what may be the world’s greatest predator: disease…In this illness-driven arms race, organisms that produce offspring from multiple mates are more likely to produce some children with the right antibodies to survive the next generation of viruses, bacteria and parasites…For Gowaty, there are many open questions remaining when it comes to female mating habits, whether in fruit flies or other organisms.”

Though Gowaty is the first to recreate Bateman’s experiment, there have long been questions about Darwin’s theory of sexual selection. Bateman’s statement that “there is nearly always a combination of an undiscriminating eagerness in the males and a discriminating passivity in the females” is demonstrably false, since females of many species mate with several males. Here are several other aspects of Bateman’s Principle that have long been in question:

Females can be promiscuous.

1. Females in many species do have more offspring when they mate with a larger number of males.

2. Mating with multiple males increases the likelihood of finding the strongest genetic compatibility.

3. Offspring fitness increases with heterogeneous mating, i.e. hybrid vigor. Females sneak copulations with men outside the group.

4. Many female mammals seek multiple partners to confuse paternity and prevent infanticide by the father.

5. In some species, copulation and fertilization are separated by several months. Females hedge their bets by mating with several males in order to increase the likelihood of fertilization.

Sperm is not always cheap.

6. In some species, sperm require substantial energy to produce enough to fertilize the female’s eggs.

7. Some species require repeated copulations to stimulate ovulation. A female lion may require 100 copulations from one male to initiate pregnancy.

8. Some species reverse roles, with males doing the majority of the parental care.

9. In some species, males prioritize mate guarding over sexual variety, challenging Bateman’s finding that males are more reproductively successful with more mating partners.

10. Species that spawn have either equal investment by both sexes, or in some cases, the production of gametes requires more energy from males.

Male display is often a warning rather than a pickup line.

11. Evolutionary musicologist Joseph Jordania has observed that many species display bright colors, ornaments, vocalizations, and various antics as warning displays.  According to him, most of these warning displays were erroneously attributed to the forces of sexual selection.

There is certainly ample evidence in our own society that unrestrained female sexuality increases promiscuity, so perhaps this should come as no surprise. Still, I find the implications of this rather dizzying. While the theory of sexual selection has not been disproved, its most important study has been, returning us to the realm of unconfirmed hypotheses.

If promiscuity is reproductively advantageous for both sexes, then both should regard monogamous commitment as a sacrifice, or at least a tradeoff. In a time when women’s earning power is climbing steadily, the potential effects of women’s choosing multiple mating partners may already be observed.

  • What will this mean for the family? 
  • Are we headed for a Bacchanalian nightmare that makes hookup culture look like child’s play?   
  • Will it be economics that ultimately drives us back into monogamy?
  • Will the pendulum swing back soon, or will a crisis in number of surviving offspring be required to change course? 
  • What does this mean for HUSsies and others who prefer the intimate love relationship to the “zipless f*ck?” Will they succeed in creating and sustaining the relationships they crave?

Don’t kill the messenger, but if monogamy is unnatural from a biological standpoint, and all the baggage around female promiscuity really is cultural, then the next hundred years or so should be interesting and frightening. 

For the record, this doesn’t change a thing I’ve been recommending here for 3+ years. If it’s monogamy, marriage and family you want, you can still have it using the same strategies. But hurry. We may be the 21st century equivalent of the Pompeiians, witnesses to the volcanic eruption that was the Sexual Revolution.