Nature did not invent flight once. Count the hardware and you get at least four separate inventions: insects, airborne over four hundred million years ago with membranes stretched between rigid veins; pterosaurs, whose fossils turned up in 1784 and whose wing, one researcher showed, was a genuinely separate solution; birds, flying for roughly the same span of time that bats and sugar gliders have been apart; and bats, the only mammals with true powered flight. The technical reality, as ever, is under the hood, and a 2023 paper in Science Advances goes straight to it.
The study starts from an embarrassment of convergent evolution. As many as seven living groups of mammals took to the air independently, from flying squirrels to marsupial possums to the colugo, a primate cousin. Every one glides on the same trick, a skin membrane between the limbs called a patagium. The question the authors asked is whether that membrane was reinvented each time or inherited. In the sugar glider, a marsupial, the patagium forms after birth, in the mother’s pouch, which gave the researchers a live window into its construction.
The detail that matters is a gene called Wnt5a. Its levels track the first skin changes, a bunching-up of the dermis called condensation and a thickening of the epidermis called hyperplasia. Dose cultured skin and engineered mice with extra Wnt5a and those early hallmarks switch on by themselves. Bats, placental mammals separated from the sugar glider by some 160 million years, show nearly the same Wnt5a pattern in their flank membranes. So, remarkably, does the outer ear of an ordinary lab mouse, a structure nearly every mammal carries with no flying ancestry at all.
Read that again. The machinery for building a wing surface predates wings. Gliders and bats set off on separate journeys into the air carrying a shared “molecular toolkit”, inherited from a common ancestor, and the same kit most likely sits in humans, doing things not yet understood. The pterosaurs, by contrast, grew their own solution to almost 12 m (39 ft) and some 127 kg (280 lbs) in Quetzalcoatlus northropi before vanishing around the K-T extinction some 65 million years back. Four inventions, and the mammalian one was less an invention than a renovation.
The authors are candid about the gaps. There is no flying mouse; precisely how Wnt5a does its work remains unknown. But the wider point stands. Birds answered the question of flight, in one account, “with difficulty”, and mammals answered it repeatedly, with borrowed parts; as the authors put it, “trying is in our DNA.”
Sources
- Marsupials and other mammals separately evolved flight many times, and we are finally learning how
- Flight, that is the Question | Dragon Theories | The Circle of the Dragon
