Chapter 8: The Cook’s Journey

The Gene’s Journey

In this final chapter, Wrangham summarizes the points in human evolutionary history that were influenced by the use of fire and the nutritional benefits of cooked food. Because I have already touched on many of these morphological and social changes, I wanted to zero in on a concept Wrangham mentions briefly in chapter eight: the “Thrifty Gene Hypothesis.” I had never heard of it before doing this extra research, so I figured it deserved further explanation.

The “Thrifty Gene Hypothesis” “…claims that because the environments of our hunter-gatherer ancestors were highly seasonal, we are physiologically adapted to periods of feast and famine. Accordingly, ancestral humans supposedly digested and stored energy in their bodies with exceptional efficiency” (Wrangham, 2009).  This idea was first purposed in 1962 by American population geneticist James Neel (McDermott, 1998). Neel (1962) sought to explain the apparent genetic predisposition for diabetes. In his research, he concluded that obese people with diabetes had genes that caused them to intake more food, and store these calories better.  Neal (1962) stated that people with this genotype had suppressed blood sugar levels that caused them to be hungry more frequently and to eat more as a result. He believed that this was an ancestral adaption, as Wrangham stated, for famine survival.

Wrangham states that this theory is no longer accepted, and that obesity is rather viewed as “a result of eating exceptionally high-energy, calorie dense foods, rather than from ancient adaptation to seasonality” (Wrangham, 2009). However, he doesn’t explain WHY the thrifty gene idea was tossed away.

Speakman (2008) states simply that the thrifty gene never had enough time to evolve. This genotype would have had only approximately 12,000 years to spread into 30% of our population (the percent which suffers from obesity).  Famines do not exert a high selective pressure, with a mortality rate of only 5-12% (Speakman, 2008).  Beginning with modern hominid ancestors in Africa around 2 million years ago, this gene would have had to be passed down successfully through the famine survivors for about 100,000-70,000 generations (Speakman, 2008). Especially considering that the same source states most deaths in famine are actually caused by cholera, typhoid, diarrhea and other illness, anti-starvation genes simply haven’t had enough time to become so dominant.

References:

McDermott R. 1998. Ethics, epidemiology and the thrifty gene: biological determinism as a health hazard. Social Science & Medicine. 47:1189-1195.

Neel J. 1962.  Diabetes Mellitus: A “Thrifty” Genotype Rendered Detrimental by “Progress”? Am J Hum Genet . 14:353-362

Speakman J.R. 2008. Thrifty genes for obesity, an attractive but flawed idea, and an alternative perspective: the ‘drifty gene’ hypothesis. International Journal of Obesity. 32:1611-1617.

Wrangham, R. 2009. Catching fire: how cooking made us human. New York: Basics Books.