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Sexual selection upended: The fatal flaw in Bateman’s 1948 study

Recently, we noted that Bateman’s theory of sexual selection was going the way fo all Darwinism – crumbling under the weight of evidence.

Here’s the open access paper.

In “UCLA biologists reveal potential ‘fatal flaw’ in iconic sexual selection study” (Physorg , June 26, 2012) Kim DeRose unpacks some of the issues: The theory was that male fruit flies “gained an evolutionary advantage” in terms of spreading their genes through promiscuous mating while females did not. The immediate extrapolations are not hard to guess …. No one had tried duplicating this most-cited study on sexual selection since it was published in 1948. And when they did, a fatal flaw was discovered:

Imagine the child of a curly-winged mother and an eyeless father. The child has an equal chance of having both mutations, only the father’s mutation, only the mother’s mutation or no mutation at all. In order to know who mated with whom, Bateman used only the children with two mutations, because these were the only ones for which he could specifically identify both the mother and father. But by counting only the children with two mutations, Bateman probably got a skewed sample, Gowaty said. In repeating Bateman’s experiment, she and her colleagues found that the flies with two severe mutations are less likely to survive into adulthood.

Flies use their wings not only to hover but also to sing during courtship, which is why curly wings present a huge disadvantage. Specimens with deformed eyes might have an even tougher time surviving. The 25 percent of children born with both mutations were even more likely to die before being counted by Bateman or Gowaty.

This obvious problem wasn’t addressed, perhaps not even noticed by the generations of Darwinians since then.

Confirmation bias, yes; the study confirmed what they already believed. But this is a deeper issue: Not wanting to look at the idol’s feet, just in case the unbelievers are right about the clay.  When we are doing that, we know at some level that the feet really are clay.

From DeRose:

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, she said. Those who blindly accept that females are choosy while males are promiscuous might be missing a big piece of the puzzle.

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, a thirty-year veteran in the area, established, using molecular genetics, that females in monogamous social species regularly mated with other males. She thinks female promiscuity confers a wider variety of protection from disease.

We also have human and mammalian biases to consider. Darwin and Bateman were assuming, for example, that the female has a choice about mates; in many species, that’s far from clear. We also naturally assume that females are more burdened than males by reproducing. But it may not be true of, say, a female snake who just lays her eggs and slithers away. These aren’t overt biases; more like hidden assumptions that direct our attention to one scene rather than another.

As Gowaty says,

“Paradigms are like glue, they constrain what you can see,” she said. “It’s like being stuck in sludge — it’s hard to lift your foot out and take a step in a new direction.”

All this said, long after Bateman’s work is disconfirmed, it’ll still be mandated for education standards, stoutly defended by the Darwin lobby. ;)

Here’s the open access paper.

Here’s the Abstract:

No evidence of sexual selection in a repetition of Bateman’s classic study of Drosophila melanogaster

Patricia Adair Gowatya,b,c,1, Yong-Kyu Kimd,e, and Wyatt W. Andersond,1

We are unique in reporting a repetition of Bateman [Bateman AJ (1948) Heredity (Edinb) 2:349–368] using his methods of parentage assignment, which linked sex differences in variance of reproductive success and variance in number of mates in small populations of Drosophila melanogaster. Using offspring phenotypes, we inferred who mated with whom and assigned offspring to parents. Like Bateman, we cultured adults expressing dramatic phenotypes, so that each adult was heterozygous-dominant at its unique marker locus but had only wild-type alleles at all other subjects’ marker loci. Assuming no viability effects of parental markers on offspring, the frequencies of parental phenotypes in offspring follow Mendelian expectations: one-quarter will be double-mutants who inherit the dominant gene from each parent, the offspring from which Bateman counted the number of mates per breeder; half of the offspring must be single mutants inheriting the dominant gene of one parent and the wild-type allele of the other parent; and one-quarter would inherit neither of their parent’s marker mutations. Here we show that inviability of double-mutant offspring biased inferences of mate number and number of offspring on which rest inferences of sex differences in fitness variances. Bateman’s method overestimated subjects with zero mates, underestimated subjects with one or more mates, and produced systematically biased estimates of offspring number by sex. Bateman’s methodology mismeasured fitness variances that are the key variables of sexual selection.

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