The word adaptation does not stem from its current usage in evolutionary biology but rather dates back to the early 17th century, when it indicated a relation between design and function or how something fits into something else. In biology this general idea has been co-opted so that adaptation has three meanings. First, in a physiological sense, an animal or plant can adapt by adjusting to its immediate environment—for instance, by changing its temperature or metabolism with an increase in altitude. Second, and more commonly, the word adaptation refers either to the process of becoming adapted or to the features of organisms that promote reproductive success relative to other possible features. Here the process of adaptation is driven by genetic variations among individuals that become adapted to—that is, have greater success in—a specific environmental context.
Organisms can adapt to an environment in different ways. They can adapt biologically, meaning they alter body functions. An example of biological adaptation can be seen in the bodies of people living at high altitudes, such as Tibet. Tibetans thrive at altitudes where oxygen levels are up to 40 per cent lower than at sea level. Breathing air that thin would cause most people to get sick, but Tibetans’ bodies have evolved changes in their body chemistry. Most people can survive at high altitudes for a short time because their bodies raise their levels of haemoglobin, a protein that transports oxygen in the blood. However, continuously high levels of haemoglobin are dangerous, so increased haemoglobin levels are not a good solution to high-altitude survival in the long term. Tibetans seemed to have evolved genetic mutations that allow them to use oxygen far more efficiently without the need for extra haemoglobin.
Organisms can also exhibit behavioural adaptation. One example of behavioural adaptation is how emperor penguins in Antarctica crowd together to share their warmth in the middle of winter.
Over time, environments can change and become drier, wetter, hotter, colder, darker or sunnier. Since adaptations develop to help animals survive in a specific habitat, what happens if the environment begins to change, and those adaptations no longer help the animal? If an animal's food source disappears, adaptations that help them find that food will no longer be useful. Sometimes even a small change in temperature or water quality can mean big problems for animals that have adapted to survive under certain conditions. Altered environments have meant extinction for some animals. When habitats change, in order to survive animals must either move to new areas, or respond to those changes through adaptations. For example, a species living in water that becomes more acidic might adapt by slowly shifting its own body chemistry.
Adaptations may cause an increase or decrease in populations of animals with certain traits. An example of a changing adaptation is the case of the peppered moth. The peppered moth uses camouflage to blend in with the trees it perches on, in order to avoid being eaten by birds. About 200 years ago, light-coloured peppered moths were common, while dark-coloured peppered moths were rare. The lighter moths were more difficult for birds to see against the light-coloured tree trunks and light-coloured lichen on the trees, so they were more likely to survive. However, during the Industrial Revolution many forests became polluted with layers of black soot from the burning coal used in factories. Trees became darker, and the light-coloured lichen was gone. The lighter moths stood out against the dark trees and became easy prey for birds. After the trees became darker, the dark-coloured moths were better camouflaged and less likely to be eaten. They became more likely to survive and pass on their dark-coloured genes to their young. Over time, the dark coloured moths became the more common of the two-colour forms.
How would you like to live in the forest, hunt and gather your food, and use hand motions and grunts to talk to your friends and family? Millions of years ago, that's how our ancestors lived. Over the years, humans adapted to their changing environments by changing how they acted and looked until they became the most sophisticated species on Earth. Humans have hundreds of special features that help us survive, called adaptations, but we're only going to look at a few of the most important that really set us apart from other animals.
Bipedalism is just a fancy way of saying that we walk on two feet. Pretend you're racing a friend, at walking speed. Your friend just uses his or her feet, but you must keep your feet and hands on the ground. Who do you think would win? It's more likely that your friend would reach the finish line first because walking with just your feet is faster, and you don't have to use as much energy. Over time, our ancestors began walking on two legs, and eventually, their bodies changed so that they walked this way all the time.
This adaptation allowed early humans to use their hands for other things like using tools, picking and holding plants, and carrying babies. Having their heads up higher also let humans see their surroundings better. Other animals, such as some apes and birds, also use two feet at times, but humans are the only mammal that uses bipedalism as their main way of getting around.