Scientists have revealed desirable traits, like being lean and healthy, can become more common in a population over generations without changing a person's genetic code.
Researchers at Sydney's Victor Chang Cardiac Research Institute say characteristics can become more prevalent via "epigenetic changes" which can also be reversed.
Epigenetics examines how genes are switched on and off, often through an environmental change.
Researchers fed mice a diet rich in folate and zinc, which suppressed obesity by turning a particular gene off.
They found that when the diet was continued in the lean mice over five generations, the epigenetic effects were inherited and the proportion of lean and healthy mice in each subsequent generation increased without changing their genetic code.
Study leader Cath Suter said it was interesting to note the reversibility of the diet-induced epigenetic changes.
"When we took the diet away from the mice, we found that the proportion of healthy and lean mice stayed the same for a generation or two, but then dropped off again," she said.
"This kind of reversibility could be very advantageous if a change in environment was only temporary, say, a change in climate.
"Populations could adapt quickly but retain the ability to revert back if necessary."
Co-author Jennifer Cropley said it could no longer be accepted that evolutionary changes only occurred through genetics.
"Over the years, we've come to accept that genetic changes underlie Darwin's theory of evolution and natural selection - that a chance genetic mutation occurs in a person, and if it's desirable or advantageous, it will be passed on through generations and eventually populations," she said.
"What this study gives us is a new way of understanding how we might have evolved and how populations can rapidly adapt to new environments.
"Genetic changes take many thousands of years to spread through a population, but with epigenetic changes, a whole population could change much more rapidly because epigenetic changes can occur in multiple individuals simultaneously and potentially be passed on by all of them."