We tend to think of diseases like Alzheimer's and dementia, and other age-related degenerative diseases, as dysfunctions that prevent us from having a normal, healthy old age. But that turns out to be the wrong way to think about these conditions, from an evolutionary perspective.

In fact, a healthy old age is a biological oddity, and is only enabled in humans by fairly recently acquired mutations that have cropped up in the human lineage. Dr. Ajit Varki, Distinguished Professor of Medicine and Cellular & Molecular Medicine and the Centre for Research and Training in Anthropogeny, at the University of California, San Diego, and a team of colleagues, have found that many of the gene variants that are most protective against age-related dementia and other diseases are newly evolved in humans. On the other hand, those variants that are associated with the greatest risk are more similar to those in chimps and other more distant relatives.

Dr. Varki suggests that this is part of the evolutionary response to our extended post-reproductive life, which is thought to be a selective advantage for raising grandchildren.

- Paper in PNAS
- UCSD release
- Science news article
- NPR story