Of the millions of animals on Earth, including the relative handful that are considered the most intelligent - including apes, whales, crows, and owls - only humans experience the severe age-related decline in mental abilities marked by Alzheimer's disease.
To Bruce Yankner, professor of pathology and neurology at Harvard Medical School (HMS), it's pretty clear that evolution is to blame.
"Something has occurred in evolution that makes our brain susceptible to age-related change," Yankner said in a talk Thursday night (March 25) sponsored by the Harvard Museum of Natural History as part of its "Evolution Matters" lecture series.
Yanker, whose HMS lab studies brain aging and how getting old gives rise to the pathology of Alzheimer's and Parkinson's diseases, said Alzheimer's is one of the most rapidly emerging diseases of this century. As medical science lengthens human lifespan, the proportion of the population that is elderly is growing. Considering that as many as half of those over age 85 develop Alzheimer's, there is a growing urgency to understand the disease more fully and to develop more effective interventions.
"It is clear that cognitive impairment and defcline is one of the emerging health threats of the 21st century," Yankner said.
Yankner said that scientific evidence shows that some cognitive decline - beginning in middle age and accelerating after age 70 - is normal as we grow older. This decline is also seen in other animals, inlcuding mice and monkeys.