The principle of coevolution- Darwin’s astonishing predictive powers

In the years following the publication of On the Origin of Species, Charles Darwin became famous for his work on evolution. But he also had a reputation for his specialist knowledge – including on the biology of orchids.

In 1862 Darwin was sent a specimen of an unusual Madagascan orchid, which produced flowers with nectar at the base of a 25-cm- (10-in-) long trumpet. Darwin made a prediction: Madagascar must be home to a species of insect with a tongue that was 25cm (10in) long. His prediction was based on the idea that two or more species influence each other’s evolution, or coevolve – although the term “coevolution” wasn’t coined until the 1960s. Darwin might never have used the word, but he was conscious of the importance that the principle of coevolution might play in nature.

A famous example involves the initial appearance of flowering plants. In Darwin’s time the fossil record suggested that flowers burst onto the scene in the geological equivalent of the blink of an eye. This bothered Darwin, who believed that species evolved very gradually. Gaston de Saporta suggested the mystery might be explained by what scientists would now call coevolution. Perhaps flowers evolved so rapidly because they coevolved with insect pollinators, and this sped up the usually slow process of evolution. Darwin thought de Saporta’s idea was “splendid” (although scientists now think it was probably wrong, not least because fossils found since Darwin’s day show flowers evolved more gradually than once thought).

And what of Darwin’s prediction? About 20 years after his death, biologists found a species of Madagascan moth with an extraordinarily long tongue. In 1992, scientists confirmed that the moth does indeed feed on nectar from the unusual orchid.

Darwin suggested that some species of flowering plant have entered into an “evolutionary pact” with some species of insect. Flowers produce sweet nectar that provides insects with nourishment, while the insects (unwittingly) carry pollen between flowers as they sup on the nectar, helping the plants fertilize each other and produce viable seeds. If a plant has evolved flowers with difficult-to-reach nectar it stands to reason that an insect must have evolved a tongue to take advantage of the food.

Biological species don’t evolve in a vacuum. The evolutionary path a species takes is modified by its environment.

This means two or more species in the environment might end up influencing each other’s evolution.