Monday, 22 September 2014

Recent Human Evolution in Quebec

Evidence for evolution in response to natural selection in a contemporary human population.

Scientists from Canada and the UK have recently discovered compelling evidence for an example of local rapid human evolution in an isolated community in Quebec, Canada, between 1800 and 1940, when the age at first birth for women fell from 26 to 22 years old in Ile aux Coudres, a small island community of French Canadians in the Gulf of St. Lawrence, about 80 Km Northeast of Quebec City.

Creationists will no doubt take comfort from the fact that the paper mentions the term 'microevolution' which has been misrepresented to their victims by creationist pseudo-science frauds as materially different to 'macroevolution', although real scientists recognise no such distinction in terms of the mechanism of change - which is what we are talking about here.

I have never seen a coherent explanation of how an identical mechanism of both microevolution and macroevolution can be both possible and impossible at the same time, so perhaps a creationist can explain this for me... or maybe not, after all, it's just a slogan intended for those who prefer slogans to thinking.

As the authors of the paper in question say:

Darwinian evolution is often perceived as a slow process. However, there is growing awareness that microevolution, defined as a genetic change from one generation to the next in response to natural selection, can lead to changes in the phenotypes (observable characters) of organisms over just a few years or decades.

I am inclined to have faith in the analyses since they are established within the quantitative genetic community. Evolution, gene frequency change, can work in a hurry and is working all the time in our species.

Henry Harpending, Anthropologist, University of Utah
To make matters worse for Christian creationists, the evidence for this evolution was due in large part to their own superstition as the evidence was found in the detailed births, marriages and deaths records meticulously recorded by the local church in an overwhelmingly exclusively Christian community at a time when membership of the church was, for all practical purposes, obligatory.

What makes the evidence compelling is not so much the fact of a change in the age at first birth, but the pattern of that change which is close to the pattern seen in known examples of genetic evolution. The team ruled out improved nutrition and general health because this would have been expected to be reflected in a reduced infant mortality rate, which wasn't seen. Similarly, changes in local culture as the transition during the period from predominantly farming to a mixed of professions.

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.

Culture shapes the selection pressures acting on the age at first birth and the reproductive history of women in this population. The cultural context was favoring the selection of some genes.

Emmanuel Milot, Département des Sciences Biologiques, Université du Québec à Montréal, Montréal, QC, Canada.

By using statistical techniques to predict likely results from two groups subject to different sets of assumptions and dividing each set into eight cohorts spread over the period 1800 - 1940 the team found that the closest correlation to what really happened to breeding success defined as the number of births reaching the age of 15 years old, was that predicted for genetic change.

The team argue that this is evidence that not only is human evolution still continuing - some authorities even report finding evidence of it speeding up - but that evolution can be detected over just a few generations, even for a long-lived species like Homo sapiens.

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