Physicist, Startup Founder, Blogger, Dad

Wednesday, October 05, 2011

Fast evolution in Quebec

These researchers find evidence that genes lowering the age at first reproduction (AFR) became more prevalent over 140 years in a small isolated population for which they had detailed ancestry records. See also this NYTimes article.

I haven't read the paper yet, so can't comment on the result. Environmental confounds might be tricky, but I suppose the result is basically that children of low AFR mothers tend to also have low AFR and that AFR dropped systematically in the population due to greater fitness (effective fertility) of low AFR women over the 140 years.

Those pesky allele frequencies, they are not constant in time ;-)

Evidence for evolution in response to natural selection in a contemporary human population (PNAS)

It is often claimed that modern humans have stopped evolving because cultural and technological advancements have annihilated natural selection. In contrast, recent studies show that selection can be strong in contemporary populations. However, detecting a response to selection is particularly challenging; previous evidence from wild animals has been criticized for both applying anticonservative statistical tests and failing to consider random genetic drift. Here we study life-history variation in an insular preindustrial French-Canadian population and apply a recently proposed conservative approach to testing microevolutionary responses to selection. As reported for other such societies, natural selection favored an earlier age at first reproduction (AFR) among women. AFR was also highly heritable and genetically correlated to fitness, predicting a microevolutionary change toward earlier reproduction. In agreement with this prediction, AFR declined from about 26–22 y over a 140-y period. Crucially, we uncovered a substantial change in the breeding values for this trait, indicating that the change in AFR largely occurred at the genetic level. Moreover, the genetic trend was higher than expected under the effect of random genetic drift alone. Our results show that microevolution can be detectable over relatively few generations in humans and underscore the need for studies of human demography and reproductive ecology to consider the role of evolutionary processes. (Italics mine)


5371 said...

Seems absurd, as if the authors had no idea that these people came to Quebec from a radically different physical, social and economic environment.

esmith said...

Between infant mortality, disease, violence and emigration, the effective number of offspring should be much lower. I'd estimate that dropping AFR from 26 to 22, assuming reduced fertility at 40 and menopause at 45, would increase the number of children surviving to maturity by about 25%.

5371 said...

More likely they are no genes at all. Wealth (or modest economic independence) is not a biologically heritable trait.

5371 said...

Guppies don't need permission to reproduce. And even in their case, there are plenty of explanations for those changes other than an alteration in gene frequencies. For instance, an improved environment during development may have effects on the adult phenotype that continue to increase for generations.

LaurentMelchiorTellier said...

I wish that were the case. Sadly, there was no adoption control group, or even an apology for the lack of one. Their only nod towards controlling for environment/culture is to control for intra-sample homogeneity.

ben_g said...

Wealth is heritable.  Age at first childbearing is heritable.  Nearly every trait you look at is significantly heritable. 

You don't seem to understand what heritable means.  It simply means that genetic variation ultimately causes phenotypic variation in a given environment.  In the most direct causal pathway, I have a gene which you don't so we get different proteins.  In a more complex pathway, I have genes which alter the direction of my brain's development so that I am more conscientous or intelligence, which in turn alters my financial decisions, which in turn makes me wealthier than you.

5371 said...

post hoc, non propter hoc

5371 said...

The fact that my son takes over my bag of gold when I die does not make my bag of gold a biologically heritable trait. I would have thought this pretty uncontroversial.

ben_g said...

The trait in question is receiving a bag of gold, not the bag itself.  This trait is mainly environmental-- it's based on having been raised by you rather than having certain inherited characteristics.  A twin study would find that being an identical twin doesn't make you much more similar for gold-receiving than if you were a dizygotic twin.  An adoption study would find that your adopted son was similarly likely to receive an inheritance.  There is a small genetic component, though-- traits that indear your son to you play a role in whether he receives an inheritance.

It's really easy to mock heritability from a point of ignorance.  What's needed is clarity of thinking rather than folk definitions of "genetic" and "environmental", etc.

5371 said...

Clarity of thinking makes it very obvious that selection of genetic traits was unlikely to be a factor in Quebec.

LaurentMelchiorTellier said...

I highly enjoy the precision of your definitions, Ben. 

But this is also why I encourage you to distinguish markedly between heritability, and Breeding Value. Heritability is a broad sense term, and includes all pathways, however indirect. It is possible, in this sense, to inherit a bag of gold, a religion, and a language. Breeding Value, however, is direct genetic pathways ONLY (!). IE, nature ONLY (!), nurture/environment/indirect causation is purely a confounding factor to be controlled for. 

Do you see why it's important to distinguish between the two in this study?

MtMoru said...

And the Aran Islands men are called boys until 40. Very late reproductive age on these islands off Ireland's west coast. How long have they been inhabited? Not long.

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