Another risk is loss of human rationality, while preserving human life. In a society there are always so many people with limited cognitive abilities, and most of the achievements are made by a small number of talented people. Genetic and social degradation, reducing the level of education, loss of skills of logic can lead to a temporary decrease in intelligence of individual groups of people. But as long as humanity is very large in population, it is not so bad, because there will always be enough intelligent people. Significant drop in population after nonglobal disaster may exacerbate this problem. And the low intelligence of the remaining people will reduce their chances of survival. Of course, one can imagine such an absurd situation that people are so degraded that by the evolutionary path new species arise from us, which is not having a full-fledged intelligence — and that back then this kind of evolving reasonable, developed a new intelligence.
More dangerous is decline of intelligence because of the spread of technological contaminants (or use of a certain weapon). For example, I should mention constantly growing global arsenic contamination, which is used in various technological processes. Sergio Dani wrote about this in his article “Gold, coal and oil.” http://sosarsenic.blogspot.com/2009/11/gold-coal-and-oil-regulatory-crisis-of.html, http://www.medical-hypotheses.com/article/S0306-9877 (09) 00666-5/abstract
Disengaged during the extraction of gold mines in the arsenic remains in the biosphere for millennia. Dani binds arsenic with Alzheimer’s disease. In his another paper is demonstrated that increasing concentrations of arsenic leads to an exponential increase in incidence of Alzheimer’s disease. He believes that people are particularly vulnerable to arsenic poisoning, as they have large brains and longevity. If, however, according to Denis, in the course of evolution, people will adapt to high levels of arsenic, it will lead to a decline in the brain and life expectancy, resulting in the intellect of people will be lost.
In addition to arsenic contamination occurs among many other neurotoxic substances — CO, CO2, methane, benzene, dioxin, mercury, lead, etc. Although the level of pollution by each of them separately is below health standards, the sum of the impacts may be larger. One reason for the fall of the Roman Empire was called the total poisoning of its citizens (though not barbarians) of lead from water pipes. Of course, they could not have knowledge about these remote and unforeseen consequences — but we also may not know about the many consequences of our affairs.
In addition to dementia is alcohol and most drugs, many drugs (eg, side effect in the accompanying sheets of mixtures of heartburn called dementia). Also rigid ideological system, or memes.
Number of infections, particularly prion, also leads to dementia.
Despite this, the average IQ of people is growing as life expectancy.