The Red Queen Hypothesis

The Red Queen in Through the Looking-Glass runs to stay in place. The hypothesis named after her says populations may need ongoing evolutionary change to maintain success as other species evolve. Success means surviving and reproducing. Inherited traits pass from parents to young and can become more common over generations. Animals do not choose new inherited traits because they need them. The hypothesis does not say every species changes all the time.

Bats locate prey using echoes from their calls. Some moths hear these calls and turn away. Some moths also produce clicks using sound-producing organs. In some species, those clicks disrupt bat echolocation. Ears detect sound; other structures produce the clicks. A moth defence can favour bat traits that improve hunting, such as quieter calls. This is a possible response, not a guaranteed next step.

Myxomatosis is a disease caused by myxoma virus. After the virus was introduced to control rabbits in Australia, many infected rabbits died. Inherited resistance became more common as resistant rabbits left more offspring. Virus strains changed too. Here the rabbit is the host and the virus is a parasite. Changes in host resistance can affect selection on the virus, and changes in viral infection traits can affect selection on the host.

Mosquitoes and fleas can carry myxoma virus between rabbits. A longer infection can offer more chances for transmission. That does not mean every virus evolves to become harmless or less deadly. Which variants spread depends on the conditions. Viruses do not plan to help their hosts. Evolution concerns differences in which variants spread, not intentions.

Darwin used a Madagascan orchid's deep nectar spur to predict a long-tongued moth. A suitable moth was described later. Nectar feeds the moth, while pollen carried between flowers helps the orchid reproduce. This beneficial partnership can favour changes in both species. Matching shapes alone do not prove how both traits evolved. A deep tube suggests looking for a visitor able to reach its nectar; it does not prove an exact tongue length.

Co-evolution means two species evolve because each affects selection in the other. Changing at the same time does not prove that link. A predator can favour prey defences; prey defences can favour predator traits that overcome them. Different interactions can favour different adaptations, adding to biodiversity. Other processes shape variety too. Arms races can slow or end when conditions change. Neither equal changes nor a permanent winner is guaranteed.