Alzheimer’s Disease Evolved With Human Intelligence

A new study, which was published in BioRxiv, shows that researchers are coming to the conclusion that Alzheimer’s disease has evolved with human intelligence. The study has found that between 50,000 and 200,000 years ago, natural selection ended up changing six genes that were involved in the development of the human brain. These changes could have increased the neurons connectivity, which is important for making humans smarter as they evolved from their hominin ancestors. However, the increases in intellectual capacity did come with some negative effects, such as those genes being blamed for Alzheimer’s disease.

Alzheimer's Disease1

Kun Tang, who is a population geneticist at Shanghai Institutes for Biological Sciences in China led the study, and Tang is speculating that as the aging brains struggled with the new metabolic demands by the increased intelligence, Alzheimer’s disease developed out of that. The only people or animal known to have Alzheimer’s disease is people, and it’s even absent in the closely related primates like Chimpanzees, so there is something in the human genes that have allowed Alzheimer’s to manifest. This is the first study to really determine that there are possibilities within evolution that could be responsible for Alzheimer’s disease, which opens the door for doctors to look at other treatment options.

Tang and his colleagues began researching modern human DNA for the evolutionary evidence. The researchers began looking at the genomes of 90 people who were African, Asian, and European descent. They were looking for patterns in terms of the variation driven by the changes in natural selection and population sizes.

It was hard for the researchers because the two things mimicked each other, so they wanted to control for the effects of the population changes. The researchers isolated the signatures of natural selection by estimating how the population changed over a period of time. The researchers then decided to identify the genome segments that were not matching with the population history, which revealed that the DNA stretches were more likely shaped by natural selection.


The researchers were then looking back at events that happened over 500,000 years ago, which showed the evolutionary forces that helped shape the modern human. This was thought to have been about 200,000 years ago. The other methods that could look at these changes could only go back about 30,000 years, so the approach Tang is using is new and very promising. Tang is using all different types of selection in a uniform framework, and he is also treating the eras of selection in a more or less uniformed manner. There will be more research needed in order to figure out whether or not this new method can be used in a broader application.

What is the most interesting about this new approach is that it can look at the African people, who go back further in time than the Asian or European people. Asian and Europeans were thought to come from only a small group of people who left about 60,000 years ago. Since Tang’s method allows you to go back further in time, you can look at the genomic-analysis of Africans from over 300,000 years ago. This new method will allow researchers to look at the evolutionary development of humans in a new way, especially when things like natural selection and population changes can be accounted for. The researchers are hoping that this new method will be able to be used in a broader way across all types of scientific situations, including evolutionary changes in animals or other groups of people. There is also hope that doing things like this can not only find out how Alzheimer’s disease happened, but a lot of other neurological and health conditions that impact millions of Americans and people all over the world. If researchers can find the genes behind other types of medical issues, then there would be new ways to look at treatment, and there could be new revolutionary treatments available for diseases that we did not think could be changed through modifying molecules.


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Jeanne Rose
Jeanne Rose lives in Cincinnati, Ohio, and has been a freelance writer since 2010. She took Allied Health in vocational school where she earned her CNA/PCA, and worked in a hospital for 3 years. Jeanne enjoys writing about science, health, politics, business, and other topics as well.

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