1Every living species on Earth has changed slowly and steadily over many millions of years.
2This slow process, which is known as evolution, helps animals and plants survive in their environment.
3Animals that cannot adapt quickly to changes in their surroundings may eventually die out completely.
4The peppered moth in England is a very famous example of rapid natural selection at work.
5Before the industrial revolution, most of these moths were pale, hiding easily on light tree bark.
6When factory smoke turned the trees black, pale moths became easy targets for hungry birds.
7Darker moths survived and reproduced, so within a few decades most moths in the cities were dark.
8Camouflage is only one of the many clever adaptations that are found throughout the natural world.
9The arctic fox grows a white coat in winter and a brown one in summer.
10Desert cacti store water inside their thick stems so that they can survive long droughts.
11Even humans continue to adapt, although modern medicine and technology have completely changed the rules.