The only genetic changes in humans we ever hear about are those producing diseases such as cystic fibrosis. Has anyone identified any genetic changes within recent generations that make individuals possessing them 鈥渕ore fit鈥� to thrive in today鈥檚 environment? Would we even know these changes if we saw them? And would we consider them normal for healthy humans?
鈥� The example that is most often cited of a positive genetic change within a recent generation is that of sickle-cell anaemia, which appears to confer an advantage to people who have it in places where malaria is endemic. While we wouldn鈥檛 necessarily consider having sickle-cell anaemia as a healthy trait, carrying a copy of the 鈥渇aulty鈥� gene confers a level of resistance to malaria, and is therefore selected for in populations exposed to malaria parasites.
鈥淪ickle-cell anaemia appears to confer an advantage in places where malaria is endemic鈥�
Advertisement
This is generally taught in most high-school biology courses as an example of human natural selection, as well as the idea that a trait is neither positive nor negative intrinsically: rather, its value is dependent on the environment.
However, another example of a positive trait that is necessary for survival in today鈥檚 environment is our adjustment to being able to cope with the high level of sodium in our diet.
In populations that have a low daily salt intake, such as some indigenous Amazonians, people can retain salt effectively; they lose less sodium in their sweat and urine compared with average citizens of the US. If they are subsequently exposed to a high-sodium diet, however, this ability to retain salt works against them, and many may suffer from hypertensive disorders and die at a very young age from heart disease.
鈥淪ome indigenous Amazonians lose less sodium in their sweat than average citizens of the US鈥�
Mark Bilger, Livonia, Michigan, US
We pay 拢25 for every answer published in New 杏吧原创. To answer this question 鈥� or ask a new one 鈥� visit newscientist.com/lastword. Terms and conditions apply.
This article appeared in print under the headline 鈥淪elected selections鈥�