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Environments can change naturally over time, and, if this happens slowly, living things may adapt to these changes.
This is called evolution. Charles Darwin was the first person to explain evolution in the 1800’s.
Within one species, some individuals will have traits which are better suited to the environment than others which mean that they have a higher chance of survival.
This individual therefore, survives better than those without it, and so passes this trait on to its offspring. This is known as ‘survival of the fittest’.
Eventually, the individuals without the trait all die out and the species has gone through evolution.
Traits can become desirable due to a change in the environment, and this is called a selection pressure.
Peppered moths are a good example. Before the industrial revolution, trees were covered in lichen which is light in colour. This meant that the moths had light speckles on their wings so that they could be camouflaged, preventing them from being eaten by predators. The industrial revolution led to an increase in air pollution which reduced the amount of lichen on trees, meaning that the light coloured moths were not camouflaged anymore and so were eaten by predators. Moths which had darker speckles survived, and the species evolved.