But it may take several thousand years before they are completely eradicated.
Scientists at Cambridge and Colombia universities discovered that genetic variations associated with these illnesses were less common in people who lived longer.
Those who survive to an older age are more likely to successfully pass on their genes than people who die relatively young meaning these traits for good health become more common in the human gene pool, the researchers said.
The study, published in the journal PLOS Biology, suggested that natural selection is slowly eliminating negative traits to adapt to our changing lifestyle.
It said even genetic variants with late onset effects, such as those linked to Alzheimer’s, were being “weeded out”.
“It’s a subtle signal, but we find genetic evidence that natural selection is happening in modern human populations,” said Joseph Pickrell, one of the study’s authors.
In theory, illnesses such as Alzheimer’s could be wiped out of the human species within a few thousand years.
The team studied the genetic make-up of 150,000 Britons and 60,000 Americans to analyse human evolution.
It also discovered that people who were genetically pre-disposed to hitting puberty later and those who had their first child later in life were living longer.
A one-year delay in puberty lowered the death rate by 3-4 per cent, while a one-year child-bearing delay lowered the death rate by 6 per cent.
The researchers said traits linked to longer lifespans now may not be useful in the future as conditions change.
To better understand genetic mutations and why they arise, researchers will need to study “millions of samples in the pipeline”, they said.