Wings — four inventions, four materials
Reference: Evolution of flight
Powered flight was arrived at at least four separate times by unrelated lineages — and each one built the wing out of something different. Nothing was copied from anything.
The four
- Insects — the first, and the odd one out: insect wings are not modified legs. They are separate structures, and an insect keeps all six of its legs as well. Their evolutionary origin is still genuinely argued over, with current evidence pointing at a dual origin combining body-wall outgrowth and tissue from the leg base.
- Pterosaurs — a membrane stretched along one enormously elongated fourth finger.
- Birds — feathers on a modified forelimb, with the hand bones fused. Feathers came first, for insulation and display, and were recruited for flight afterwards.
- Bats — skin stretched across four elongated fingers. A bat flies on its hands, and the thumb is still free and clawed.
Three of the four are vertebrates, and all three paid the same price: the forelimb stops being an arm. A bird cannot carry anything in its wings. A bat hangs by its feet because its hands are busy being wings.
What repetition on this scale means
The same solution reached four times from four starting materials is the strongest single argument that the environment is doing the specifying. Air has fixed properties. Anything solving flight in it converges on an aerofoil, because there is not much else that works.
The honest counter-reading is available and worth stating: repeated arrival at one solution is also what a shared specification would look like. This section does not settle that. It records which features recur, how many times, and out of what — and the recurrence is real either way. Where the two readings genuinely differ is limb count, because a specification could freely have issued six, and no vertebrate ever got them.
Every creature on this axis
| Creature | Wings |
|---|---|
| Horse | None |
| Bat | Skin on four fingers |
| Whale | None |
| Eagle | Feathered forelimbs |
| Shark | None |
| Octopus | None |
| Dragonfly | Four — not modified limbs |
| Frog and salamander | None |
| Snake | None |
| Oak | None (seeds may be winged) |
| Dragon Traditional | Membranous, additional to the legs |
| Pegasus Traditional | Feathered, additional to the legs |
| Griffin Traditional | Feathered, additional to the legs |
| Centaur Traditional | None |
| Sphinx Traditional | Present in the Greek form, absent in the Egyptian |
| Phoenix Traditional | Feathered forelimbs |
| Mermaid Traditional | None |