Posts Tagged ‘natural selection’

It’s 10 O’Clock. Do you Know Where Your Genes Are?

October 5th, 2011

There was a very important story in the New York Times on October 4, 2011 about obesity but you are forgiven if you missed it.  The piece, by Nicholas Wade, tells the story of research on the histories of childbirths on an island in the St. Lawrence River, 50 miles northeast of Quebec. What they found was that the age at which women had her first child fell to 22 years from 26 years from 1799 to 1940. What did you miss? Well, it turns out that the age at which a woman has her first child is a highly heritable trait. And what this finding means is that humans are still evolving.  Statistical tests allowed the researchers to distinguish between the effects of natural selection and changes in cultural practices. Natural Selection Leaves Fresh Footprints on Canadian Island –

(Readers may recall that the above time-frame is not unlike that employed in The Techno-Physio Revolution, which documented the rise in body weight over 350 years.)

 Not only are humans still evolving but that evolution is occurring faster than many assume.  The DNA sequence can only identify large changes sweeping through a population. But phenotypic or bodily data can provide information on more recent changes.  Wade cites a review article of 14 studies. The lead author, Stephen C. Stearns of Yale,  stated, “We had three general aims: first, to correct the still widespread misconception that natural selection is not operating on contemporary humans; second, to make quantitative predictions about future evolutionary change for specific traits with medical significance; and third, to register firmly a point of general cultural interest that follows directly from our first two aims: We are still evolving, and for some traits we can make short-term predictions about our future evolution.” In this study, the authors found that the descendants of women in the Framingham Heart Study, begun in 1948, are predicted to be on average slightly shorter and stouter, to have lower total cholesterol levels and systolic blood pressure, to have their first child earlier and reach menopause later than they would in the absence of evolution. Colloquium papers: Natural selectio… [Proc Natl Acad Sci U S A. 2010] – PubMed – NCBI 

Jeffrey Friedman noted in the essay I quoted yesterday, “natural selection can be observed in a single generation as nature weeds out the maladapted under changing environmental conditions, leaving the more highly adapted individuals to proliferate. Thus, rapid changes in population characteristics are generally the result of a gene/environmental interaction.” 

What does this have to do with obesity? Well, in discussions about the genetic basis of obesity, skeptics often comment is often that increases in the prevalence of obesity (basically in the last 50 years) cannot be the result of genes because the gene pool or natural selection does not change that rapidly. Yet, evidence to the contrary continues to mount. While no one may be sure just how fast the genome is changing, it is probably inaccurate to say that it cannot change quite rapidly. 

Indeed, an examination of 23 studies reporting data from 14 different countries between 1998 and 2008, indicates a high prevalence of overweight and obesity in pre-school children age 2-5 years, in middle and high income countries, among both well-off and low income segments of populations, in both rural and urban areas and among all ethnic and racial groups represented. Global prevalence of overweight and obesity in… [Anthropol Anz. 2011] – PubMed – NCBI