Over the past year, I have been working on programs to prevent and treat chronic malnutrition in several indigenous communities in rural Guatemala. Chronic malnutrition, also known as “stunting,” is the result of a complex social and biological interplay and manifests in children who are very short for their age. Children who are short tend to grow up into adults who are not only short, but also who tend not to reach their academic, economic, and health potential.
It is hard to overstate the burden of chronic malnutrition in Guatemala. With a rate of stunting at approximately 50%, Guatemala has the highest rate of chronic malnutrition in the Western Hemisphere and the third highest rate in the world. Even among its Central American neighbors and income peers, Guatemala’s burden of chronic malnutrition is striking:
Moreover, the World Bank estimates that indigenous children are twice as likely to suffer from stunting as non-indigenous children in Guatemala. In the rural communities where Wuqu’ Kawoq works, we often encounter rates of stunting greater than 70%. In fact, in one of our poorer communities where we monitor the growth of over 200 children ages 6 months to 5 years, every single child in the community is below the WHO median height-for-age.
Thinking about the height of my patients on a daily basis has led me to a simple question: What is the relative importance of nature vs. nuture on the empiric reality that Maya indigenous people in rural Guatemala are short? In other words, if one could remove the social forces that influence chronic malnutrition–deep poverty, food insecurity, lack of education, low access to quality health care services, inadequate land holdings–and look directly into the genes, what would be the average height of a cohort of indigenous children and adults?
This is the question I will try to reflect upon in this post. Here are the some key points I’ve learned.
1. It is difficult to find well-nourished indigenous populations to study.
I’m not the first person to wonder about the influence of nature vs. nuture on the height of indigenous people in Guatemala. This question also interested investigators in the famous Guatemalan INCAP trial. In a 2010 article reviewing the 50 years of the INCAP trial (Martorell 2010), one researcher offered this shocking admission:
The question of what relative importance to give to racial ancestry and to the nutrition–infection complex as causes for the differences in attained growth among Central American populations has been of interest to INCAP through its history … An obvious approach would be to compare the growth of well-nourished children of the various racial groups among themselves and with the reference population. However, the problem of studying certain groups, such as the Mayan people of Guatemala, was and still is that it is difficult to find well-nourished indigenous populations. (Emphasis mine.)
In other words: One reason we don’t know how tall Maya indigenous populations might be is that malnutrition is universal in their communities. That is, there is no affluent, well-nourished Mayan community from which to draw baseline data.
2. In explaining differences in height in preschool children, social class is much more important than ethnic background.
This finding comes to us from a Lancet article from 40 years ago:
Comparisons among preschool children, presumably well nourished but of different ethnic background, indicate that differences in height and weight are relatively small–3% for height and about 6% for weight. In contrast, differences between these children and those, often of similar ethnic and geographical background, who live in the poor, urban and rural regions of developing countries approach 12% in height and 30% in weight. Thus, differences in growth of preschool children associated with social class, are many times those which can be attributed to ethnic factors alone. Therefore, height and weight standards chosen to represent optimal preschool growth can be drawn from studies of well-to-do already published children, regardless of race or ethnicity, because any racial or ethnic effect on mean preschool growth is small compared with environmental effects. (Emphasis mine.)
In other words, the effect of environment is greater than the effect of genes in explaining why a given group of children is short. Therefore, we should not rely on ethnic explanations for short stature when considering why Maya preschool children are short in our communities.
3. Maya children who grow up in the United States are taller than Maya children in Guatemala.
In 2010, ABC conducted a feature on Wuqu’ Kawoq’s nutrition program. As part of this program, our organization produced images of 9-year-old Maya children in a Guatemalan community and images of 9-year-old Maya who have grown up in Florida. The two photographs are shown below. Note how much taller than U.S.-raised children appear compared with their Guatemalan counterparts.
The claim made in this photo is not just a television trick. In a 2002 paper in the American Journal of Human Biology entitled “Rapid Change in Height and Body Proportions of Maya American Children,” researchers documented the incredible “plasticity” of linear growth in Maya children. Using datasets from multiple Maya communities in the U.S., the authors show that, on average, Maya American children aged 5-12 years are 11.5 cm taller than Maya children living in Guatemala.
In other words, if you take Maya children from poor families out of their Guatemala communities and put them in the U.S. with access to even minimal services, the children grow much taller.
4. Using long-bone data to estimate height, archaeologists have found that the pre-conquest people were taller than the modern Maya.
The best review of height among the pre-Hispanic Maya comes from a book chapter by Lourdes Márquez and Andrés del Ángel in Bones of the Maya. These authors conclude that the modern day sample of long-bone data generally suggests the lowest height of all cultural periods. According to their estimates, modern skeletons are about 2 centimeters shorter than Classic (A.D. 250-900) and Postclassic (AD 900-1500s) Maya and roughly 4 centimeters shorter than Pre-Classic (before A.D. 250) Maya.
Discerning the cause of this reduction in height is complex. However, one hypothesis is that the social turmoil of the Spanish Conquest created the very environment that has hindered the growth potential of Maya people and made malnutrition ubiquitous in Maya communities.
Although I am not on expert on the genetics of height, my own reading of the literature has led me to the believe that nuture, rather than nature, is a much more powerful explanatory factor when thinking about the height of indigenous Maya people. Although ethnic variation may play a role in the ultimate ideal height in this population, it is currently impossible to discern how much of a role given that Guatemalan indigenous communities suffer from such high rates of chronic malnutrition, poverty, and social exclusion.
One of my colleagues at Wuqu’ Kawoq frequently talks to indigenous mothers about these issues. Here is what she says:
Y k’o winäq a esque man nik’ïy ta ri ak’wal porque herencia porque ri rati’t alaj raqän porque ri rumama e alaj raqän tonces xub’än heredar pero man keri ta röj alaj qaqän porque man xb’an ta jun buena nutricion chiqe durante que ri embarazo y durante que xojk’ïy.
[And people say that the child is not growing because of its genes, because their grandmother was short or their grandfather was short, therefore they inherited being short, but that is not true. We are all short because we did not receive good nutrition during pregnancy and when we were growing.]
This is the message we want to send to the families of our malnourished children. We know these communities are poor, so we make sure to offer this message without any kernal of blame. At the same time, we try to help families understand that it is not herencia (inheritance) that makes their children short but rather environmental, economic, and social factors.