I spent the weekend helping my sister work on her dissertation. She is at MIT studying the role of eugenics in urban planning and architectural design in South America. So most of my weekend was spent reading about how in the early to mid 1900s  scientists, physicians and public health scientists in particular, promoted the underlying idea that the way to improve our society was to promote “desirable” populations. In most instances, their actions were appalling by today’s standards (such as determining desirable and non-desirable immigrants based on morphology), but often the line that separates old eugenic ideas and today’s theories was much more difficult to see. Was their effort to isolate people with communicative diseases so that they don’t ‘contaminate’ the superior healthy population that much different than some of today’s practices? Or for example, was the French Lamarckean version of eugenics, which believed that populations could be improved by manipulating the environment even in the presence of ‘undesirable’ genetic traits, that much different than our current “gene by environment interaction” research?

The tone has definitely changed (no current mainstream scientist speaks in terms of improving particular populations over others -aka explicit racism), and the underlying intentions have also changed from promoting desirable populations to alleviating suffering and improving health among all. Yet, I can’t help but to think back to the old french members of the “Museo Social” when I read about ‘intelligence’ research. I am not in any way suggesting that the authors of the study I’m about to describe promote eugenic principles. Instead, I bring this point simply to open the discussion about those difficult to spot lines between current science and the early twentieth century eugenic thoughts that drove most of medical research at the time.

So what am I talking about?

In the latest issue of Pediatrics a team from Universities in Singapore, Australia, Canada, and New Zealand, reported the findings of an epidemiological study on the association between birth size and later IQ. Birth weight has been associated with cognitive performance in that children who are born significantly underweight (such as premature kids) tend to have cognitive deficits (ranging from simply lower IQ to severe deficits) when compared to kids that are born within the normal birth size range. Less is known however, whether variations within this normative range, such as variations in weight, length, or head size, also affect the kids’ future intellectual capacity or cognitive performance.

The authors studied a cohort of 1979 Asian (Singapore) children who attended mainstream schools and were participating in a large longitudinal study of risk for Myopia. Birth data were abstracted from the kids’ medical charts. IQ was measured using the Raven’s Progressive Matrices test when the kids were in 2nd to 5th grade. The Raven’s is a test of non-verbal reasoning which has been used as a proxy for intelligence (more on this later).

The results:

  1. Greater body length, body weight, and head size were all significantly associated with increases in IQ scores.
  2. For every 1Kg (2.2lb)  increase in body weight, the model predicted a 2.19 increase in IQ score. For every 1cm increase in length the model predicted an increase of 0.37 points in IQ
  3. IQ was not associated with gestational age
  4. An analysis of a sub-sample of siblings showed that the taller (at birth) sibling had significantly higher IQs that the shorter sibling.

In sum, the data seem to suggest that prenatal factors affecting body weight likely impact brain developmental processes that are associated with later cognitive performance.

Sorry I’m being highly introspective in this post, but as I type I’m wondering why this article made me think about the eugenic issues I read this past weekend. Maybe I’m also reacting to Richard Nissbett wonderful lecture at the American Psychological Society two weeks ago regarding the role of culture and environment on IQ.  So I will end this post early by simply addressing three issues: 1) I’m confused about the distribution of scores on their IQ measure and the norms used to reach those scores. Either this was not a representative population sample, or the norms used were outdated leading to significantly higher IQ estimates than expected in the population. Please note that even the low birth weight and ‘short’ siblings had higher IQs than expected in the general population. 2) It is not quite accurate that the Raven’s is highly correlated with IQ. In fact, the authors used a citation of a study conducted in 1956 that used measures that have been obsolete for decades. Instead, most recent research with newer IQ scales show that the Raven’s progressive matrices tap only at some aspects of IQ and their IQ estimates are not highly correlated with full IQ scores obtained from current full batteries. Finally,  IQ in early to middle childhood is highly fluid and not a strong predictor of later IQ. Thus, I would love to see the developmental trajectory of these kids and examine more applicable outcomes such as educational attainment, etc.

The reference: Broekman, B., Chan, Y., Chong, Y., Quek, S., Fung, D., Low, Y., Ooi, Y., Gluckman, P., Meaney, M., Wong, T., & Saw, S. (2009). The Influence of Birth Size on Intelligence in Healthy Children PEDIATRICS, 123 (6) DOI: 10.1542/peds.2008-3344

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8 Responses to Big babies, big heads, big IQ, and thoughts on eugenics.

  1. Josh Breding says:

    It seems to me that how tall a baby is shouldn’t have an effect on its IQ.

  2. JulieL says:

    Interesting article, though it seemed to leave out some major factors that could provide these IQ deviations as well. First, I did not see notation of how many males/females were in this group. Then I noticed the group was then compacted by eliminating all other ethnic groups, thus leaving all individuals whom were of Chinese descent. The authors state: “Previous studies showed that environmental factors seem to weaken the association between BW and cognitive skills.31 Our sibship analyses were performed to exclude family environmental factors.” But I did not see this explained and due to the social implications in Asia, especially from China, in bias for parental attention to children directly due to birth order and sex, this provides a wide range of social implications for these outcomes. Perhaps they meant environmental factors which excluded social factors. They also lay the strength of their hypotheses on the subship analysis of the twins, which they state did not have a significant statistical outcome. Too much was implied on the health parameters of the groups used, not enough on social bias. Or at least I did not see this properly explained, could be an oversight, but still I don’t think it was really covered.

  3. JulieL says:

    On eugenics today, I think they still exist under other guises. Genetic counseling is a mixed blessing. While we can learn about what can be passed down to the next generation, I fear our society puts to much emphasis on these factors. The population of Down Syndrome children aborted has increased much due to these testing, as well as other genetic diseases/syndromes etc. While one could argue the possible positive aspect on social implications, the negative is there as well, thereby raising the question what deficits should social be seen as acceptable versus something to eradicate. We see this debate raging in the deaf community, whereby many parents refuse cochlear implants with the reasoning that this destroys their community, which they see no deficit in. Also we see this in the autistic community as well, some going so far as to say the mere definition of autism is corralling a population into something that should be feared versus a population that should be given parameters of acceptance.

    There are many hidden aspects of eugenics all over, from neighborhoods erased, transportation systems left w/out proper funding, emphasis on language preference, etc. Lends one much to think on.

    • Thanks Julie, you are totally correct. Eugenics may not be as explicit as it was in the last century, and most people who endorse would never admit it or use the word, but the practice is still prevalent throughout society. N.

  4. Marie Levesque says:

    I don’t buy this study. Why? Because there are other studies stating that
    large heads and bodies can be a sign of autism.


    New Research May Reveal Previously Undetected Autism Subgroup
    Individuals with large heads share other similar features

    New research from an international team of scientists has found that a large body size—in addition to a large head—is associated with autism. While previous studies have consistently found that large head size, or macrocephaly, is more frequent in people with autism, the new study led by Antonio Persico, M.D. of the University “Campus Bio-Medico” in Rome found that a subset of people with autism had an abnormally large body size, or macrosomy. They also found that this group of individuals had a higher incidence of immune disorders. This research takes an important step toward defining subtypes within the autism spectrum, which will help pinpoint the cause of and appropriate treatments for autism. [snipped]

  5. Nikki says:

    I think this is nonsense! Environmental factors are much stronger predictor of IQ than being a fat baby. Asians tend to have average or below average babies yet they tend to generally be smarter because of environmental factors.

  6. PhatnNasty says:

    Who is to say that we are smarter than people with autism….the brain is just functioning differently, not necessarily functioning less….so maybe the big head theory is correct and we need to re-focus our understanding of IQ in autistic children

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