Read more: 鈥�Unnatural selection: How humans are driving evolution鈥�
Perch in Lake Windermere in the UK used to live to a ripe old age. While the average age of fish caught and released by researchers was around 5 years, a few individuals were as old as 20. Then in 1976, an unidentified disease wiped out 99 per cent of adult fish and continued to preferentially kill older fish for years afterwards. Since then, no fish older than 7 have been caught.
According to of the University of Oslo, Norway, the perch (Perca fluviatilis) evolved very quickly in response. They now become sexually mature at an earlier age, which increases their chances of breeding before they get killed by the disease ().
Advertisement
While the disease is thought to have spread naturally in the lake, Ohlberger points out that many devastating disease outbreaks in plants and animals are a result of human activity. To mention just a few: Dutch elm disease was caused by fungi introduced from Asia; lions were hard hit by canine distemper spread by village dogs, and corals are far more susceptible to diseases when water temperatures are abnormally high, which is happening often as a result of climate change.
Anything that kills a significant proportion of a population has the potential to bring about very fast evolution. In frogs there is now some evidence of this: last year several research groups reported that some populations appear to be becoming resistant to a fungus that has decimated many amphibian species. It is also clear that human populations have sometimes evolved rapidly in response to diseases such as kuru, which attacks the nervous system.
So it seems plausible that by spreading diseases or creating the conditions in which they thrive, humans are indirectly forcing many organisms to evolve. 鈥淚 think this is a common phenomenon and has not yet been described because it is simply hard to prove,鈥� says Ohlberger. He points out that the long-running capture-and-release programme at Lake Windermere, which began in 1943 and just happened to coincide with the disease outbreak in perch, is pretty unique. In most cases we know too little about what populations were like before disease outbreaks to be able to tell if and how they have evolved in response.
Read next article: 鈥�Unnatural selection: The arms race against pests鈥�
