This is the inaugural post of my new blog “Science Itches”. In the last couple of years I have become increasingly annoyed by the amount of obsolete terms and concepts, used in anthropological and biological sciences, that have no current scientific basis but keep being used left and right. Most of these concepts are racist-based and sex-biased and regardless of massive amounts of evidence discrediting them, they have lingered around and are still part of the contemporary scientific language used by many, but questioned by very few.
One of these concepts, that makes me itch a lot, is the concept of “genetic potential”. Genetic potential is a murky notion, and one that either assumes or may lead to the belief that some human groups and individuals are, in some way, superior to others. Therefore, it implicitly assumes that some other groups will be of “inferior” condition. However, nobody was ever able to measure, assess, or provide any scientific evidence for the existence of such a thing as a “genetic potential”, for anything meaningful. Why, then, are so many people still using and writing about it as if it is an unquestionable certainty? We read about “genetic potential” in relation to intelligence, sports prowess, maths ability, artistic skills and so on. I will not approach these ones on this first scratch. My aim today is to dedicate all my enthusiasm to the concept of “genetic potential for height” and, hopefully, scratch it to smithereens, for good.
This idea of “genetic potential for height” assumes that some human groups are “by nature” shorter than others. This assumption then becomes a curse, a self-fulfilling prophecy because if a group is assumed to be “genetically” short, than nothing needs to be done in terms of health care, education and political stability, among other developments sorely needed, to try and improve their height status… or in other words, their health status.
The Maya from Guatemala and Mexico were, for a long time, considered the “pygmies” of Latin America” (1).
By establishing a “genetic potential for very short stature” it is automatically assumed that these groups are “fine” and “adapted” to their environment (normally of extreme poverty and deprivation). However, when the Maya started migrating to the US and benefited from clean drinking water, basic health care, much lower rates of infection load, extended education, enough food and a peaceful environment then the average stature of the school children increased almost 11cm, in less than one decade (2). What are these Maya doing? Defying their genetic potential? Overcoming it, in fact? How does one overcome his/her genetic potential, I wonder?
A similar change in height also happened in Japan, between the 1950s and the 1970s (3). Suddenly, the population grew unexpectedly taller…why? Mainly, because of the changes in dietary patterns that started including a much higher daily consumption of milk and dairy products (4). Got milk? Indeed they did… and that showed.
We could go on and on, for a long time, discussing changes in the stature of, virtually, all human groups in the world. We would find that associated to their average stature are powerful environmental determinants. Negative factors such as famines, war, poverty, low educational levels, infections and, in a way, everything we consider “bad” will shrink the average stature of a group. Positive factors such as decent living conditions, generalised basic health care, social stability, education for all (especially for mothers and girls), empowerment of women within the community and, generally, factors we consider “good” will increase the stature of a group. The infinite numbers of studies on positive secular trends in height show exactly this. The term “secular trend” is also in need of a scratch, but I will leave it for now as it is.
Let me make a parenthesis here to mention the Ef
e, from the Democratic Republic of Congo, who are one of the shortest human groups on record. In this particular case, citing a good summary on the topic written by Barry Bogin (5): “…a genetic defect in the cellular mechanisms for the production, release, or cellular reception of IGF-1 is the cause of [their] short stature…” (pp. 375-376). In this particular case, there is an identifiable genetic cause for the very short stature of the Efe. These are the exception, not the rule.
We do have something that some may call “genetic potential for height” but that is a species trait. This means that it applies to all human beings, to all Homo sapiens. It implies the existence of a desirable range of values for stature that is not associated with pernicious health outcomes. Many studies have shown the disadvantages of very short stature not just in terms of health outcomes but also in terms of economic production and other life components (6–10). On the other hand, being too tall has been linked to specific illnesses and with some types of cancers (11). More cells in a body means a greater likelihood that some of these cells take a wrong turn and go nuts — and that is what cancer is about: cells going nuts. Also, being too tall has negative effects on job allocations, professional promotions and, especially for women, a much reduced likelihood of reproductive success because most men can’t deal with women taller than themselves.
Bogin (12) does a very organized summary of these short-and-tall matters in the February issue of the 1998 edition of the Discovery Magazine.
Arianne Cohen, being a very tall girl herself, wrote a very informative book, “The Tall Book”, that details the good and bad of being too tall. Edda Baumann-von Broen, who is also not short, made a film called “Tall Girls” that adds a lot of information on this tall topic.
There is massive amount of evidence that links trends in the stature of a population to the quality of the environment in which they live. There is absolutely nothing that points towards a genetic potential (whatever that may mean) for stature. What it means is that there is the need for political and socioeconomic will power to improve the living conditions of the very short groups of people. And that is very time consuming, costs money and effort and requires the demolition of many prejudices that have been established for a long time, with the idea of dividing people between more and less deserving groups. As scientists we have the obligation of dismantling these wrongful, prejudicial ideas from the past and use our research for real impact, for impact that matters and that can really change the lives of the next generations.
For me, I pledge to continue fighting against the use of murky concepts like “genetic potential”.When I review papers for journals, I can guarantee that anybody using this concept will be kindly asked to “not use it”. I normally send some very long ramblings about this on the “confidential comments for the editors” section of the reviewers page if the term “genetic potential” is used. Then I try to be constructive and positive on my feedback for the authors. But this is not a term that should be used anymore in any peer-reviewed journal. My graduate students are advised, from the very beginning, to question these terms and concepts before using them blindly. In fact, I created an online list of resources that have to be read by everybody who wishes to do graduate work with me. We will then engage in a fruitful discussion that ends up in an agreement of the adequacy of several concepts.
And that’s all for now…the scratching is done and the itching has subsided.
1. Diamond J. A Question of Size. Bigger is better, right? So why in the world have Pygmies opted for smallness? Discovery. Discover Magazine; 1992. p. 3.
2. Bogin B, Smith P, Orden AB, Varela SMI, Loucky J, Varela Silva MI. Rapid change in height and body proportions of Maya American children. American journal of human biology : the official journal of the Human Biology Council [Internet]. 2002 Jan [cited 2012 Jun 11];14(6):753–61. Available from: http://apps.isiknowledge.com/full_record.do?product=UA&search_mode=GeneralSearch&qid=3&SID=R1cpkcCnh62l76NcHPd&page=1&doc=47
3. Tanner JM, Hayashi T, Preece MA, Cameron N. Increase in length of leg relative to trunk in Japanese children and adults from 1957 to 1977: comparison with British and with Japanese Americans. Annals of Human Biology [Internet]. 1982;9(5):411–23. Available from: http://informahealthcare.com/doi/abs/10.1080/03014468200005951
4. Takahashi E. Secular trend in milk consumption and growth in Japan. Human Biology. 1984;56(3):427–37.
5. Bogin B. Patterns of Human Growth. 2nd ed. Cambridge: Cambridge University Press; 1999. p. 455.
6. Barac-Nieto M, Spurr GB, Lotero H, Maksud MG, Dahners HW. Body composition during nutritional repletion of severely undernourished men. Am J Clin Nutr. 1979;32(5):981–91.
7. Spurr GB. Physical activity and energy expenditure in undernutrition. Prog. food & nut. sci. 1990;14:139–92.
8. Spurr GB. Nutritional status and physical work capacity. Yearbook of Physical Anthropology. 1983;26:1–35.
9. Wang Y, Wang X, Kong Y, Zhang JH, Zeng Q. The Great Chinese Famine leads to shorter and overweight females in Chongqing Chinese population after 50 years. Obesity (Silver Spring, Md.) [Internet]. Nature Publishing Group; 2010 Mar [cited 2012 Apr 21];18(3):588–92. Available from: http://www.ncbi.nlm.nih.gov/pubmed/19779478
10. Smith PK, Bogin B, Varela-Silva MI, Loucky J, Smith BarryVarela-Silva, Maria InêsLoucky, James PKB, Smith BarryVarela-Silva,Maria InêsLoucky, James PKB. Economic and anthropological assessments of the health of children in Maya immigrant families in the US. Economics and human biology [Internet]. 2003 Jun [cited 2012 Jul 5];1(2):145–60. Available from: http://www.ncbi.nlm.nih.gov/pubmed/15463970
11. Green J, Cairns BJ, Casabonne D, Wright FL, Reeves G, Beral V. Height and cancer incidence in the Million Women Study: prospective cohort, and meta-analysis of prospective studies of height and total cancer risk. The Lancet Oncology [Internet]. 2011 Aug [cited 2013 Jun 6];12(8):785–94. Available from: http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=3148429&tool=pmcentrez&rendertype=abstract
12. Bogin B. The short and tall of it. Discovery Magazine [Internet]. 1998 Feb;40–4. Available from: http://discovermagazine.com/1998/feb#.UbCL4kDVCSo