Movers and shakers
Migration and travel
The animal world provides some stunning examples of mass migrations, such as the millions of North American monarch butterflies that migrate over 3,200 km each year to spend the winter in fir groves in central Mexico. But animal migrations may also be the result of human interventions – accidental or intentional – with sometimes unwanted knock-on effects for other populations.
The UK’s native two-spot ladybird is currently in decline due to competition with bigger, hardier harlequin ladybirds that were imported from Asia into France and Belgium to help keep aphids from damaging crops. They crossed the Channel into the UK in 2004 by flight and on fruit, vegetables and flowers from mainland Europe.
Most humans are not migratory in the same sense, but past movements and migrations of people around the globe have profoundly changed human populations today. The forced migrations of millions of Africans to Europe and America as part of the slave trade have shaped the ethnic backgrounds of those populations.
In the 21st century international travel is easier than it ever has been, so people from different ethnic backgrounds are more likely to mix up their genes by having babies together. This should mean that human populations become increasingly less isolated and less marked in their differences. The hyper-connectedness of our world also has implications for the transmission of disease. The strain of H1N1 swine flu that emerged in La Gloria, Mexico in 2009 spread across 21 countries in less than a month, even reaching New Zealand, 15,000 km away.