For the first addition to my blog I would like to talk about
the importance of peer review. Though it is not strictly speaking molecular
biology, it is important to every field of science and is gives people a good
reason to blog and read about scientific discovery. I have provided an example
of how peer review can help to evolve research on a subject.
For some time, scientists have provided evidence for or
against the idea that malnutrition and stress lead to a change in the sex ratio
at birth. For those of you not so familiar with the subject humans naturally
have slightly more male births, usually around 106 male births for every 100
female births. It had been postulated in 1973 by biologist Robert Trivers and computer
scientist Dan Willard that females in good condition, whether it was in regards
to physical hunger or economic class, would always have a sex ratio skewed in
favor of males. This of course meant that females that suffered from hunger or
were in a disadvantaged economic class would have a more balanced sex ratio at
birth, or in extreme cases even more female than male births.
This was
controversial and many people disagreed with them, however scientific studies
could not definitively prove or disprove the theory. The debate on this idea
has persisted to this current day, with many researchers publishing on both
sides of an argument, often citing papers of the opposing side in order to point
out some flaw in a previous method. I have provided four such papers at the end
of this post if you would like to read more on the subject. The first, “Maternal
undernutrition and the sex ratio at birth in Ethiopia: evidence from a national
sample” finds that there is a slight correlation between hunger and birth but
it is not definitive and to points out that previous papers that say otherwise
were statistical aberrations. The next two actually study the same famine, from
the Great Leap Forward in China, in order to disprove then prove the connection
between hunger and sex ratio. The last is a paper detailing how poor experimentation,
observation, and calculation has allowed the debate on the subject to persist
when it should be long over.
Most articles published now accept the connection
as fact. Without a peer review process would the debate have even occurred? Or
would Willard and Trivers been dismissed as crackpot theorists in 1973? My
challenge to you is to review the literature and let me know what you think. Is
there enough evidence to definitely say starvation can cause more female
births? Is it appropriate to call out past researchers on flawed methodology?
·
Maternal undernutrition and the sex ratio at
birth in Ethiopia: evidence from a national sample
By: Aryeh D. Stein, Paul G. Barnett, Daniel
W. Sellen (2004)
·
Could changes in reported sex ratios at birth
during and after China’s 1958-1961 famine support the adaptive sex ratio
adjustment hypothesis?
By: Zhongwei Zhao, Yuan Zhu, Anna Reimondos
(2013)
·
Malnutrition, Sex Ratio, and Selection A Study
Based on the Great Leap Forward Famine
By: Shige Song (2014)
·
Privation, stress, and human sex ratio at birth
By: Shige Song (2015)
Wow. Shige Song has some hard words to say here. I liked this: "randomized experiment fills the gap because, by forcing the treatment assignment to be completely independent of the potential outcomes, it replaces the unobserved counterfactual quantities in Eq. (2) with the observed ones"
ReplyDeleteIMO, as an evolutionary biologist, often the most strident conclusions are drawn in studies of human evolution, despite the fact that ethics precludes experimental designs that are most able to provide a rigorous test.
What's up with that?
Nice summary, btw, and I appreciate that you've included multiple sources from the primary literature for those who would like to read further.