What Are the Strongest Environmental Predictors of Intelligence?

Executive Summary

  • Something very little discussed on intelligence is the impact of the environment.
  • We cover what the research shows on the top intelligence predictors.


Something that many, if not most, people have a problem with is that environmental factors contribute to the development of intelligence. Under the non-biological view, all humans developed equal intelligence, and that naturally, all environmental factors were identical.

The following was published at the Royal Society Publishing on the topic of intelligence and the environment.

Infection Diseases, Temperature..etc. Tested

Multiple regression shows that, of infectious disease, temperature, evolutionary novelty and AVED, infectious disease is the best predictor of intelligence by a large margin.(emphasis added)

The effects of years of education are not significant,(emphasis added) while temperature and evolutionary novelty seem to have distinct predictive power beyond infectious disease. Although this model cannot rule out the independent effect of distance from central Africa, this effect is difficult to interpret because of the doubt cast on the theory underlying this variable (Wicherts et al. 2010a).

Although the effects of education and GDP per capita are not statistically significant when other factors are controlled for, this is not to say that these factors are not involved. A nation of more intelligent individuals is likely to produce a higher GDP, but a wealthier nation is also more able to pay for public education,(emphasis added) as well as public medical and sanitation services. An indirect link between education and intelligence may also exist, as a better-educated population may be more interested in public health measures—leading to increased IQ by reducing parasite stress—provided that education includes information about germ theory and hygiene. These sources of endogeneity must be considered when interpreting our findings (and see below). It should also be mentioned that we are not arguing that global variation in intelligence is only caused by parasite stress. Rather, variation in intelligence is probably caused by a variety of factors, including those we have mentioned here as well as factors that are yet unknown.

The Trade-Off Between The Allocation of Energy to Immune Function Versus Brain Development

If the general pathway we propose is correct, there are two plausible mechanisms by which a trade-off in allocation of energy to immune function versus brain development and maintenance may occur. First, parasitic infection may intermittently cause the redirection of energy away from brain development. In this case, during periods of infection, the brain receives fewer energetic resources, but this allocation to brain function will return to pre-infection levels during healthy periods. During periods of infection, whatever aspects of the brain that are growing and developing will suffer reduced phenotypic quality.

Second, exposure to infectious agents may cause a developmental pathway that permanently invests more energy into immune function at the expense of brain growth. In this scenario, large amounts of energy would be allocated into immune function during periods of health, as opposed to only redirecting energy during periods of infection. This could operate through a variety of mechanisms. A plausible mechanism is that higher investment in immune system is triggered by individual exposure to infectious disease at some point during ontogeny. This may include triggering from exposure to maternal antibodies while in utero.

We also propose a complementary hypothesis that may explain some of the effects of infectious disease on intelligence. As we mentioned, it is possible that a conditional developmental pathway exists that invests more energy into the immune system at the expense of brain development. In an environment where there has consistently been a high metabolic cost associated with parasitic infection, selection would not favour the maintenance of a phenotypically plastic trait. That is, the conditional strategy of allocating more energy into brain development during periods of health would be lost, evolutionarily, if periods of health were rare. Peoples living in areas of consistently high prevalence of infectious disease over evolutionary time thus may possess adaptations that favour high obligatory investment in immune function at the expense of other metabolically expensive traits such as intelligence.

Evidence for the Stronger Immune Response in Blacks

The article’s conclusion is that people of African ancestry have a biology that has placed more energy into immune system development than intelligence. Those in colder climates, do not face the infectious disease load of those in hot climates.

This is reinforced by the following study.

A Canada-US study led by Luis Barreiro, a professor at the University of Montreal’s Department of Pediatrics and researcher at the Sainte-Justine University Hospital Center, has demonstrated that Americans of African descent have a stronger immune response to infection compared to Americans of European descent. The study establishes for the first time this difference in immune responses and shows that it is mostly genetic — inherited from our ancestors and influenced by a relatively recent natural selection. The study is published today in the scientific journal Cell.

“Although we found these differences in immune responses between African and European Americans, we are still unable to demonstrate what evolutionary pressures led to the observed differences. One of our hypotheses is that in the prehistoric period, after human populations had migrated out of Africa, they were exposed to fewer pathogens (bacteria, viruses, parasites), which reduced the immune response and thus tissue inflammation. This reduction in the immune response (and inflammation) was most likely an advantage because of the adverse consequences of acute or chronic inflammation, which are major contributors to the development of autoimmune inflammatory diseases.” – Eurekalert

This shows IQ by region and the lowest IQs in the areas with the highest infectious disease load. The IQs are strongly related to the proximity to the equator. This only applies to those people who evolved in those areas. So, while Australia has a high IQ, this does not reflect the indigenous people that evolved there, called the Aborigines. The Aborigines are too small in number to have any effect on the IQ scoring in the country. Most of Australia’s population is from Europe. 


It is doubtful that the differences in the immune response in blacks and whites will be a controversial topic. The fact that whites and blacks have different mental capabilities on average is, of course, a major politically incorrect fact. Yet it is a fact. At the same time, it is considered acceptable to accept that blacks have a stronger immune system than whites (on average). However, it is doubtful that anyone cares; the observations about intelligence differences are not considered acceptable, but this research’s conclusion looked into multiple variables. Warmer regions have a higher infectious disease load — and the body’s immune system must fight them.

Biology and other fields keep finding differences between different races, and society continues following the politically correct and evidence-free assertion that there are no differences between races.