Human Intellect Backsliding From Lack of Evolutionary Pressure: Study

The human race is slowly losing its intellectual and emotional capabilities because it no longer faces extreme evolutionary pressures, new research contends.

Human intelligence and behavior require optimal functioning of a large number of genes, but the intricate web of genes that gives people these capabilities has started to backslide, the scientists said in an article appearing Nov. 12 in the journal Trends in Genetics.

"The development of our intellectual abilities and the optimization of thousands of intelligence genes probably occurred in relatively nonverbal, dispersed groups of peoples before our ancestors emerged from Africa," study author Dr. Gerald Crabtree, of Stanford University, said in a journal news release.

In the early stages of human evolution, intelligence was critical for survival and there was immense selective pressure acting on the genes required for intellectual development. But once humans achieved a certain level of evolutionary progress, they slowly began to lose ground.

The development of agriculture led to urbanization, which may have weakened the power of natural selection to eliminate mutations that caused intellectual disabilities, the researchers explained.

Based on the frequency that harmful mutations appear in the human genome and the assumption that 2,000 to 5,000 genes are required for intellectual ability, Crabtree estimated the effect that the past 3,000 years (about 120 generations) of human history have had on humans. He concluded that all people now carry two or more mutations harmful to their intellectual or emotional stability.

He noted, however, that the loss of intellectual and emotional capabilities is quite slow and it's likely that a solution will be found in the future.

"I think we will know each of the millions of human mutations that can compromise our intellectual function and how each of these mutations interact with each other and other processes, as well as environmental influences," Crabtree said.

"At that time, we may be able to magically correct any mutation that has occurred in all cells of any organism at any developmental stage," he said. "Thus, the brutish process of natural selection will be unnecessary."

Does Eating Fish During Infancy Cut Asthma Risk?

Adding fish to babies' diets during the first year of life might reduce their risk of asthma later on, a study by Dutch researchers suggests.

This window of protection appears to occur between 6 months and 12 months of age. Adding fish to the diet before that or not at all in the first year seems to carry an increased risk of wheezing and shortness of breath, the researchers said.

"This study provides insight into what the optimal timing of introduction can be for fish," said lead study author Jessica Kiefte-de Jong, from the pediatrics and epidemiology departments at Erasmus Medical Center in Rotterdam.

"The results may assist health care workers about the recommendations regarding the introduction of complementary feeding in infants," she added.

Pediatricians may not agree with the findings, however. One expert objects to feeding children fish at such a young age because of potential harms.

"I have never heard that fish is a preventive against asthma," said Dr. Antonio Rodriguez, director of pediatric pulmonology at Miami Children's Hospital.

"There is a danger of an allergic reaction feeding fish to children under 1 year of age," he said. "In addition, there is always concern about the toxicity of mercury in fish."

This is why fish is not fed to infants, he said.

Kiefte-de Jong agreed that before parents start introducing fish to their infants these findings need confirmation in a real clinical trial. She also said the researchers aren't quite sure why eating fish at this age might benefit children's lung health.

For the study, published online Nov. 12 in the journal Pediatrics, the research team collected data from a population-based study of more than 7,200 children born between April 2002 and January 2006 in Rotterdam.

Reviewing questionnaires on overall diet, the researchers looked at when parents introduced fish to their infants' diets. They also looked at symptoms of asthma that developed at ages 3 and 4 years.

Children who started eating fish at 6 to 12 months had a significantly lower risk of wheezing when they were 4 years old compared with children who began eating fish later, Kiefte-de Jong's group found.

For children who started eating fish earlier -- or not at all -- within the first year, the risk for wheezing increased at 4 years, they noted. The risk of shortness of breath increased slightly as well.

The researchers acknowledged that other factors besides when the children started eating fish might have influenced the children's breathing ability at preschool age. And the study did not prove that the introduction of fish during the first year of life prevented asthma later on.