How did flowers and their pollinators shape each other?

Flowers look the way they do because of the animals that visit them. Pollination syndromes are suites of flower traits shaped by natural selection from different pollen vectors, such as wind, water, birds, bees or flies. The traits include shape, size, colour, odour and the reward on offer. Tubular red flowers with copious nectar often attract birds, while foul-smelling flowers attract carrion flies or beetles. Flowers pollinated by wind are small and inconspicuous, with no scent and no nectar, but they produce large numbers of pollen grains.

The best-known story is Darwin's orchid. In January 1862, Charles Darwin received a box of orchids from Madagascar, including Angraecum sesquipedale, and was astonished by the length of its green spur, the tube that holds the nectar. He wrote to a friend about a nectary a foot long and asked what insect could suck it. Darwin surmised there must be a moth whose proboscis was long enough to reach the nectar at the end of the spur. As it fed, pollen would be rubbed off on its head and carried to the next orchid.

For some time the idea of a moth with a 35 cm proboscis was ridiculed. In 1903, Walter Rothschild and Karl Jordan discovered such a moth in Madagascar, which confirmed Darwin's prediction, 21 years after he died.

The orchid and the moth, the story says, shaped each other: the orchid's spur grew longer and the moth's tongue grew longer with it. Experts still debate how exactly that happened.