An aging population brings with it significantly more pensioners. (Photo : Reuters)
In a disturbing finding, researchers said Alzheimer's disease might have evolved along with human intelligence.
The factors that drove evolution of intelligence have been implicated in Alzheimer's disease, said a study by Chinese researchers posted this month on bioRxiv, a free online archive and distribution service for unpublished preprints in the life sciences.
Researchers claim to have uncovered evidence that natural selection was responsible for changes in six genes involved in brain development some 50,000 to 200,000 years ago. These genes might have made modern humans smarter as they evolved from their hominin ancestors by increasing the connectivity among brain neurons.
The rise in human intelligence, however, came at a price since the same genes have been found to be involved in Alzheimer's disease.
Alzheimer's developed as ageing brains try to cope with new metabolic demands imposed by increasing intelligence, believes Kun Tang, a population geneticist at the Shanghai Institutes for Biological Sciences in China who led the research.
Tang is interested in looking for functional human genetic variations and understanding their biological mechanism and evolutionary roles.
Humans are the only species known to develop Alzheimer's that is absent in closely related primate species such as chimpanzees. Alzheimer's accounts for 7 in 10 cases of dementia and is a degenerative and fatal disease marked early on by short-term memory loss. The average life expectancy of an Alzheimer's victim following diagnosis is three to nine years.
To reach their conclusion, Tang and his team examined the genomes of 90 people with African, Asian or European ancestry. They sought out patterns of variation driven by changes in natural selection and population size, said Nature.
They also identified genome segments that didn't support the population history, concluding the DNA stretches were most likely shaped by natural selection.
Looking back at selection events occurring 500,000 years ago revealed the evolutionary forces that shaped the early ancestors of modern humans.
Previous research into autism found the presence of higher brain functions makes humans vulnerable to complex cognitive difficulties such as autism. The same might be said for Alzheimer's.
In autism, the Fragile X syndrome prevents the production of a crucial protein known as FMRP that activates the NOS1 gene. This gene is found throughout the developing brain in humans. Crucially, NOS1 helps guide the maturation of the brain's speech and language and decision-making centers.
