Monday, June 25, 2012

Another Darwinian Pillar Falls - Bateman's Sexual Selection: 
Evolution News & Views June 18, 2012 5:28 AM | Permalink

It was a classic experiment supporting Darwin's theory of sexual
selection. It generated a catchy phrase -- Bateman's Principle -- and
launched a paradigm. But this year, a replication of Bateman's
original 1948 experiment showed his methods were so biased and flawed
that none of his conclusions are valid.

Angus John Bateman, working on fruit flies in 1948, published his
findings which became known as Bateman's Principle: the idea that
males tend to be promiscuous (because sperm is cheap) while females
tend to be choosy (because eggs are expensive). This principle, so
impressive with its math, jargon, and presumed application of the
scientific method, seemed to support Darwin's theory of sexual

It took on a life of its own, especially after R. L. Trivers in 1972
and S. J. Arnold in 1994 brought attention to it. According to Gowaty,
Kim and Anderson, who decided to test it, citations soared and
"Bateman's Principle" took on paradigmatic status. They note that
"legions of graduate students" have read the paper since it was

The Wikipedia entry on Bateman's Principle acknowledges that many
biologists have found exceptions to it; some even doubt its status as
a scientific principle. But now, for the first time, Gowaty et al.
have replicated the experiment using Bateman's own methods -- but with
the added advantage of 64 years of advances in genetics.

In short, they found that the experiment was useless. Bateman failed
to take into account biases inherent in his methods, failed to measure
factors that discounted his conclusions, and left a mess of data that
is perfectly hopeless for making predictions about fitness due to
sexual selection.

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. [emphasis
Their open-access paper, "No evidence of sexual selection in a
repetition of Bateman's classic study of Drosophila melanogaster," is
available at PNAS for those who want the details.
Of overarching concern is how a 64-year-old classic that influenced
"legions of graduate students" (and uncounted legions of undergrads,
too) was fatally flawed yet went unchallenged all those years. Thomas
Kuhn was right: paradigms govern a scientific program until anomalies
accumulate that require a new paradigm.

In this case, though, Gowaty et al. offered no new paradigm. They did
not specifically falsify the 1948 paper; as charitably as they could,
they suggested ways to test Bateman's principle (or "Bateman's
hypothesis") with better-designed experiments. Even, so, they
recognized, it would require snooping on the little fruit flies'
sexual activity, not just measuring viable hatchlings, because
"absence of offspring is not necessarily absence of mating." Their
last paragraph was more far-reaching and less charitable:

We are left wondering why earlier readers failed to spot the
inferential problems with Bateman's original study. The main
implication we take from the present study is one earlier critics
made: The paradigmatic power of the world-view captured in Bateman's
conclusions and the phrase "Bateman's Principles" may dazzle readers,
obscuring from view methodological weaknesses and reasonable
alternative hypotheses....

Many ID supporters have undoubtedly felt the same incredulity at how
so many scientists fail to spot the inferential problems in Darwinism.
They have shared the same bewilderment at the paradigmatic power of
world-view behind other Darwinian notions and catch-phrases that,
while dazzling to readers, obscure their view of alternative
hypotheses like intelligent design. The more Darwin pillars that
crumble, though, the more the view may improve.