Natural selection continues to remove bad genes

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New research indicates genes associated with Alzheimer's disease and heavy smoking are becoming less prevalent in humans, suggesting human beings are still evolving.

Axar.az reports citing Sputnik that, in a massive genomic study, covering over 170,000 people from across Britain and the United States, researchers from Columbia University, New York Genome Center and the University of Cambridge have identified a variety of individual genes and gene sets that suggest the human genome is evolving from one generation to the next.

Hakhamanesh Mostafavi, an evolutionary biologist at Columbia University in New York City, led the study. He explained that new technology was pivotal in the researchers' project.

"Natural selection is a gradual process — evolution of new features takes million of years, but they involve small changes every generation. We now have the ability to track these changes," Mr. Mostafavi told.

Most notably, genes associated with Alzheimer's disease and heavy smoking are less prevalent in people with longer lifespans, and changes in diet have seen many populations adapt to tolerate sugar lactose within the past 20,000 years.

More recently, the human shift towards city living has selected for genes that reduce the risk of contracting debilitating diseases, such as tuberculosis and leprosy — in a sense then, natural selection has taken on an "urban" character.

The team reached their findings by combining data on 57,696 individuals from the Genetic Epidemiology Research on Adult Health and Aging study with details on 117,648 participants' parents from the UK Biobank. While the findings are subtle, they indicate natural selection is still happening in modern human populations.

Gene Mutation

One example of recent evolutionary change is the frequency of a mutation in a gene labeled CHRNA3, which encodes for a subunit of the nicotinic acetylcholine receptor. The research shows a marked drop in the prevalence of this variation among men in middle age, indicating a stronger addiction to nicotine is slowly being selected out of our global population.

Another gene variation that appears to be on the way out is ApoE E4, which encodes for a type of protein that carries cholesterol and supports injury repair in the brain.

Carrying this variation of the protein increases the likelihood of developing Alzheimer's disease — and the study found a significant decrease in the gene's presence in women over 70.

It may be that men who don't carry these harmful mutations can have more children, or that men and women who live longer can help with their grandchildren, improving their chance of survival — however, Mr. Mostafavi warned against extrapolating too much from their findings.

"Our findings could provide precise information about the stage at which age these variants assert their effects in men and women. However, it's difficult to use these findings to make predictions about how humans might be in the far future, as our environments are always changing, and could impact human evolution in unpredictable ways," Mr. Mostafavi told.

In addition to those two common mutations, the researchers identified a number of other traits predicted by genes associated with shorter life spans, including higher levels of LDL (or "bad") cholesterol, higher body mass indexes, heart disease, and asthma.

Genes that delayed puberty and child-bearing also seemed to be selected for by contributing to longer lives.

Evidently, humans are still far from being in control of their own genetic destiny — and natural selection remains the key driver, quietly refining and amending genomes unbeknownst to their hosts.

2017.09.08 / 18:14
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