Read more: 鈥�Unnatural selection: How humans are driving evolution鈥�
In Finland, the tawny owl used to be mainly grey. But since the 1960s, the proportion of a brown subtype has risen fast. 鈥淭he frequency averaged around 12 per cent in the early 60s and has increased steadily to over 40 per cent nationwide,鈥� says of the University of Helsinki, whose findings were published earlier this year (Nature Communications, ).
His team that grey owls (pictured above right) have an advantage over brown ones only when there is lots of snow. As winters have become milder, the brown subtype has thrived. It is possible that this is because brown owls are better camouflaged when there is less snow, but it could also be because brown coloration is linked to another characteristic, such as higher energy needs.
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There are countless examples of how global warming is affecting life, from plants flowering earlier in spring, to species spreading to areas that were once too cold for them to survive, to birds becoming smaller. The vast majority of these changes are not genetic but due to plasticity: organisms鈥� built-in ability to change their bodies and behaviour in response to whatever the environment throws at them. At least a few species, however, like the owls of Finland, are already changing genetically 鈥� evolving 鈥� in response to climate change.
In North America, for instance, pitcher plant mosquitoes lay their eggs in pitcher plants and the larvae enter a state of dormancy in the winter months before resuming development in spring. Dormancy is genetically programmed, triggered not by falling temperature but by the shortening days. As the growing season has lengthened, mutant mosquitoes that keep feeding and growing for longer have thrived. Northern populations now go dormant more than a week later than in 1972, when studies began.
The earlier breeding of red squirrels in North America is also thought to be partly a result of genetic changes. Some families emerge earlier in spring, and they are doing better as the climate shifts.
Plants are changing too. When seed collected from field mustard plants (Brassica rapa) in California in 1997 and 2004 were grown in identical conditions, the 2004 strains flowered 9 days earlier on average (). The change was a result of drought 鈥� the plants have evolved to reproduce before they run out of water.
Rapid evolution is thus already helping some species adapt to a warming world, but it is no 鈥淕et out of jail free鈥� card. For instance, so far pied flycatchers in the UK to shift to laying eggs earlier in spring. And according to one model that specifically takes rapid evolution into account, global warming will kill off 20 per cent of all lizard species by 2080. The problem for lizards is that as the climate warms, they have to spend more time in the shade and less time feeding.
Organisms with long generation times and slow reproductive rates are the least able to evolve, says Stephen Palumbi at Stanford University. 鈥淎nd they are the ones that are already threatened. It鈥檚 a double whammy.鈥�
Even species whose evolution has kept pace with the slight warming so far will not necessarily keep up as the global temperature soars by another 4 掳C or more. Rapid evolution generally depends on the existing variation within a population, rather than on new mutations. 鈥淚t is limited to the kind of changes that can happen quickly,鈥� Palumbi says.
In fact, there is a catch-22 to very rapid evolution 鈥� the faster organisms evolve, the less able they are to evolve further. This is because fast change occurs when only a small proportion of each generation manages to reproduce, resulting in a dramatic loss of genetic diversity 鈥� the fuel for further evolution. In many cases, the size of populations will also plummet, rendering them vulnerable to extinction. 鈥淵ou could evolve really fast but just not make it,鈥� says of the University of Maine in Orono.
Read next article: 鈥�Unnatural selection: Living with pollution鈥�
