Adaptation

An adaptation is a feature of a living thing that helps it survive and reproduce in its particular environment. Adaptations can be physical (a thick fur coat, a long beak, a poisonous skin), behavioural (hibernating in winter, hunting at night), or chemical (producing antifreeze proteins, fighting off germs). Almost every feature you see in a plant or animal is an adaptation that natural selection has shaped over many generations to help the species live where it lives.

  • Three main typesPhysical, behavioural, chemicalBody shape, action, chemistry
  • Most famous adaptationCamouflageBlending in to avoid predators or surprise prey
  • Camel's humpFat storageNot water, as people often think
  • Polar bear furTranslucentNot white; looks white by scattering light
  • Time to evolveGenerationsSometimes a few, sometimes millions
  • Trade-offAlwaysEvery adaptation has a cost as well as a benefit

Three kinds of adaptation

  • Physical adaptations: features of the body itself. Long necks on giraffes, sharp teeth on lions, thick fur on polar bears, succulent stems on cacti.
  • Behavioural adaptations: ways of acting that help survival. Hibernating, migrating, hunting in packs, building nests, mimicking other animals' warning calls.
  • Chemical (or physiological) adaptations: chemistry inside the body. Antifreeze proteins in fish that live in icy water, venom in snakes, the ability to digest tough plant fibres, the ability to make oxygen-carrying haemoglobin work better at high altitude.

Camouflage: hiding in plain sight

One of the most common kinds of adaptation is camouflage: blending in with the background to avoid being eaten (or to sneak up on prey). Examples:

  • Stick insects: look exactly like twigs.
  • Leaf insects: look exactly like leaves, complete with fake bite marks.
  • Snowshoe hares: brown in summer, white in winter to blend with snow.
  • Octopuses: can change colour and texture in less than a second to match almost any background.
  • Tigers: orange stripes look obvious to us, but blend with shadows in jungle grass when seen by their prey (most of which are colour-blind in red and orange).

Extreme adaptations

Some living things have evolved adaptations to live in the most extreme environments on Earth.

  • Camels can drink 100 litres of water in 10 minutes, can lose 25% of their body weight in dehydration without dying, store energy as fat in their humps, and have triple eyelashes to keep out sand.
  • Polar bears have translucent (not white) hollow hairs that trap warm air, plus 10 cm of blubber for insulation, plus black skin underneath that absorbs heat from sunlight.
  • Antarctic icefish have no haemoglobin in their blood (the only vertebrates without it) and produce special antifreeze proteins that stop their blood freezing in -2 °C water.
  • Cacti store water in their thick stems, replace water-losing leaves with spines, open their stomata only at night, and can shrink and swell with the rainy seasons.
  • Deep-sea anglerfish have built-in glowing lures to attract prey in pitch dark, and the tiny males have evolved to fuse permanently to the females' bodies as parasites.

Adaptations always have trade-offs

Every adaptation has a cost as well as a benefit. Polar bears have wonderful warm coats, but they would overheat in any warmer climate (which is why they cannot move south as the Arctic warms). Peacocks have stunning tails that attract mates, but the tails also slow them down and attract predators. Cacti can survive the desert beautifully, but they would die quickly in a forest where other plants out-compete them for light.

This trade-off is one of the reasons every species has its own niche. There is no "best" creature, only creatures perfectly suited to particular environments.

Fact The tardigrade (also called the "water bear") is one of the most extreme survivors on Earth. These microscopic 8-legged creatures can survive being frozen to nearly absolute zero, boiled at over 150 °C, dried out for over 30 years, exposed to massive radiation, and even the vacuum and radiation of outer space (one experiment took live tardigrades into orbit on the outside of a spacecraft, and many survived). Their secret is a clever set of adaptations that let them dry out completely, suspend their biology and rehydrate later.

Adaptations are not "designed"

It is tempting to talk about adaptations as if they were "designed" for a purpose: a giraffe has a long neck "to" reach high leaves; a polar bear has white fur "to" hide in the snow. But that is a shortcut for clearer thinking. No designer planned any of these. Each adaptation is the result of many generations of natural selection, in which random variations that happened to work better were passed on more often than variations that did not.

Many adaptations are also imperfect. The human spine is a famously awkward design: it evolved from a horizontal four-legged ancestor and was not built for the constant vertical compression of standing upright. That is why back pain is so common in humans. Evolution can only work with what is already there, so it often produces compromises and quick fixes rather than perfect solutions.

Did you know? Some animals have vestigial features: leftover bits and pieces from their ancestors that no longer serve a purpose. Whales have small, useless hip bones from their land-mammal ancestors. Snakes have tiny leg bones buried inside them. Some cave fish are born with eyes that never properly develop because they have no use in total darkness. These leftovers are great evidence for evolution.
Deeper dive: convergent evolution, when different lineages invent the same trick

One of the most striking patterns in nature is convergent evolution: when completely unrelated species end up with very similar adaptations because they live in similar environments. It is one of the most beautiful pieces of evidence for natural selection.

Examples:

  • Eyes: complex camera-style eyes have evolved at least 10 separate times in different parts of the animal kingdom, including in vertebrates (us), in octopuses (completely unrelated invertebrates), in some snails, and even in a few jellyfish.
  • Flight: powered flight has evolved at least four times: in insects, pterosaurs, birds and bats. Each time the basic problem (wings, lightweight bodies, powerful muscles) was solved from completely different starting materials.
  • Streamlined fish shape: dolphins, ichthyosaurs (extinct marine reptiles), tunafish and sharks all evolved roughly the same streamlined body shape, even though they are very distantly related.
  • Echolocation: bats and dolphins both evolved sonar systems for finding prey, completely independently, on opposite ends of the animal kingdom.
  • Carnivorous plants: plant-trapping insects has evolved separately at least 9 times in different families of plant.

Convergent evolution shows that nature has a limited number of "good answers" to common problems. Given enough time and the right environment, similar adaptations will appear over and over again, even in completely unrelated lineages. It is one of the deep underlying patterns of life.

For the process behind it, see natural selection. For how adaptations build new species, see species and speciation.