When Animals Shed Their Wings

And why the sea is boiling hot— And whether pigs have wings     ~ Lewis Carroll, Through the Looking-Glass

The sea is not boiling hot, though one day (about five billion years hence), it will be. And pigs certainly don’t have wings, but it’s actually not a silly question to ask why not. It’s a kind of jokey approach to a more general question: “If such and such is so great, why don’t all animals have such and such? Why don’t all animals, even pigs, have wings?”

Many biologists would say, “It’s because the necessary genetic variation to evolve wings was never available for natural selection to work on. The right mutations didn’t arise, and perhaps couldn’t because pig embryology is simply not geared to sprout little projections that might eventually grow into wings.” I am perhaps eccentric among biologists in not leaping immediately to that answer. I would add a combination of the following three answers: “Because wings wouldn’t be useful to them; because wings would be a handicap in their particular way of life; and because even if wings might be useful to them, the usefulness would be outweighed by the economic costs.” The fact that wings are not always a good thing is demonstrated by those animals whose ancestors used to have wings but who have given them up.

Worker ants don’t have wings. They walk everywhere. Well, perhaps “run” is a better word. The ancestors of ants were winged wasps, so modern ants have lost their wings over evolutionary time. But we don’t have to go back that far. Nowhere near. The worker ant’s immediate parents, her mother and her father, both had wings. Every worker ant is a sterile female fully equipped with the genes of a queen, and would sprout wings if reared differently, as queens are. The potential for wings is, so to speak, coiled up in the genes of all ants, but in workers it doesn’t burst forth.

There must be something wrong with having wings, otherwise worker ants would realise their undoubted genetic ability to grow them. The pluses and minuses for and against wings must be pretty finely balanced if a female sometimes grows them and sometimes doesn’t.

An illustration by Jana Lenzova, showing a queen ant shedding her wings.

Queens need their wings to found a new nest far from their original home nest. Wings also enable young queens to meet winged males not from their own nest. Workers, since they don’t reproduce, have neither of these two needs. They typically spend a great deal of their time underground, crawling through confined spaces. Perhaps wings would get in the way in the cramped corridors, galleries, and chambers of an underground nest. This possibility is vividly coloured by the fact that a queen ant, having mated for the only time in her life and then having flown to a suitable place to found her new underground nest, loses her wings. In some species, she bites them off, in others she rips them off with her legs.

To bite off your own wings is pretty drastic testimony that wings aren’t always desirable. They’ve served their purpose on the mating flight and the search for a new nest site. Surplus to requirements and probably an active hindrance underground, they are thrown away. Or eaten.

Admittedly, worker ants don’t spend all their time underground. They scuttle about foraging for food which they bring back to the nest. Even if wings are a handicap underground, mightn’t it still be a good idea to keep them so the workers could forage fast like their wasp ancestors?

An illustration by Jana Lenzova, showing ants co-operating to drag a millipede.

Well, wasps may be faster than ants but consider this: Foraging ants often drag home to their nest great lumps of food heavier than themselves: a whole beetle, for instance. They couldn’t fly with such a burden. Often, they collaborate in teams to drag even larger prey. Teams of army ants have even been seen dragging a whole scorpion along. Where wasps and bees forage over large distances for small parcels of food, ants specialise in food that is relatively close to home and which can be too large to carry in flight.

Even without a full cargo, flying is very energy-intensive. As we’ll see later, wasp flight muscles are little reciprocating engines, and they burn a lot of sugary aviation fuel. Wings themselves must cost something to grow. Any limb has to be made of materials that enter the body as food, and four wings for every one of the thousands of workers in a nest would not be cheap to grow. They’d be a heavy drain on the colony’s economic resources. Probably all these considerations tipped the workers’ balance towards not growing wings.

Termites are very different from ants in some ways, not in others. When I was a child in Africa, we called them “white ants,” but they aren’t ants, not even close. Where ants are related to wasps and bees, termites are closer to cockroaches. In their evolution, they independently converged towards an ant-like way of life from their cockroach-like beginnings, as ants evolved from their wasp-like beginnings. But there are important differences between the two outcomes.

Where worker ants, bees, and wasps are always sterile females, worker termites are sterile males as well as sterile females. But they are like ants in that the workers are wingless while the reproductive females and males (queens and kings) have wings, which they use for the same purpose as winged ants. And winged termites swarm in a similar way to ants—rather spectacularly at certain times of the year. I had childhood friends in Africa who, when the winged “white ants” were swarming, used to rush about stuffing them into their mouths—and, toasted, they were a local delicacy.

As with ants, and presumably for the same reasons (termites typically spend even more time in enclosed spaces than ants), queen termites shed their wings after the mating flight. Indeed, they turn into grotesquely swollen shapes, for whom the very idea of wings would seem like a joke. The head, thorax, and legs are unmistakably those of an insect, but the abdomen is a massively bloated, fat, white bag of eggs. The queen is just a walking egg factory—actually not even a walking one, as she is too fat to walk. She’ll churn out more than 100 million eggs during her long life.

Left: A winged termite queen. Right: The termite queen as wingless egg factory.

No birds bite their wings off. It’s hard to even imagine. The only remotely similar example I can think of among vertebrates is autotomy of the tail. From the Greek for self-cutting, autotomy is the shedding of the tail, or part of it, when a predator has caught it. It’s a useful trick that has arisen many times independently in lizards and amphibians. But never in birds. Unlike queen ants, no bird autotomises its wings.

Over evolutionary time, however, plenty of birds have gradually shrunk their wings, or even lost them altogether. Especially on islands—where more than 60 species of birds today (many more if you count extinct species) are known to have become flightless: among them geese, ducks, parrots, falcons, cranes, and more than 30 species of rail, including the tiny Inaccessible Island rail of Tristan da Cunha.

Why do island birds lose the power of flight over evolutionary time? Flightless birds are often found on islands too remote to have been reached by mammal predators or competitors. The lack of mammals has two effects. Firstly, birds, having arrived on wings, are able to take over the ways of life that would normally be filled by mammals; ways of life that don’t require wings. The role of large mammals in New Zealand was filled by the now extinct flightless moas. Kiwis behave like medium-sized mammals. And the role of small mammals in New Zealand is (or was) filled by a flightless wren, the Stephens Island wren (recently extinct), and by flightless insects, giant crickets called wētās. All are descended from winged ancestors.

Secondly, given that there are no mammal predators on their island, birds “discover” that wings aren’t necessary to escape being eaten. This is, presumably, the story for the dodos of Mauritius, and related flightless birds on neighbouring islands, descended from flying pigeons of some kind.

I put “discover” in quotation marks for a reason. Obviously, those ancestral pigeons, newly touched down in Mauritius or Rodriguez, didn’t look around and say, “Oh goody, no predators, let’s all shrink our wings.” What really happened over many generations is that those individuals who happened to have genes for slightly smaller wings than average were more successful. Probably because they saved on the economic costs of growing them. They, therefore, could afford to rear more children, who inherited the slightly reduced wings. And so, as the generations went by, the wings steadily shrank.

At the same time the bodies of the pigeons got larger. You could see this as diverting to other parts of the body resources saved through not needing to grow and service wings. Flying consumes plenty of energy, and diverting all that energy into other things, including increased size, makes a lot of sense.

Excerpted from Flights of Fancy: Defying Gravity by Design and Evolution, by Richard Dawkins and illustrator Jana Lenzova, published by Apollo. Copyright © 2022 by Richard Dawkins & Jana Lenzová.


This is a companion discussion topic for the original entry at https://quillette.com/2022/05/05/when-animals-shed-their-wings/
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Would be interesting to hear what the author thinks about this:

or this:

Are Genetic Mutations Really Random? New Findings Suggest Not.

Kinda blows the last 100 years of established scientific “fact” out of the water…

Thanks, those are most interesting links.

Not really. What the articles seem to be saying, is that the rate of mutation at a particular gene, can itself be altered by natural selection.

If mutations at a particular site might be good for you, then organisms which have high rates of mutation at that site, have a better chance of healthy offspring. That’s the message of the first paper, which says that humans exposed to the risk of malaria, have higher rates of mutation in genes which could protect against malaria.

Conversely, if mutations at a particular site are usually bad for you, then organisms which have low rates of mutation at that site, will have healthier offspring - that’s the second paper, about the weed Arabidopsis.

In the second paper, they even suggest the mechanism of this selection - modification of the “epigenome”, a set of auxiliary chemical properties which affect the expression of the DNA sequence.

So it’s a new layer to natural selection, but it’s not being treated as evidence for intelligent design, if that’s what you’re thinking.

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I’ve heard of this Dawkins fellow before but can’t seem to place him…

I think a lot of New Zealanders, surrounded as we are by those flightless birds that have stepped into niches filled by mammals elsewhere, would give the same answer.

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Great comment. I would only add that I’ve read a small amount on the subject of speciation vs. gradation. I think that epigenetics are incredibly important missing piece of the puzzle. My view is that a particular epigenetic advantage will quickly become prevalent within population, if it greatly aids survival or sex selection. One would also expect a degree of feedback between the organism over the generations and the new environmental niche.

Maybe it’s like a tin opener. Perhaps the initial lever which allows a species to exploit a new niche more thoroughly then in turn opens up a whole new wave of potential epigenetic advancements tailored specifically to the new niche. I don’t think we can ignore the group level either. I’ve often wondered whether the widespread development of homosexuality in animals might be a group survival expression predicated on glacial periods- with groups which have higher ratios of adults to offspring more likely to survive than groups that don’t.

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…“I am perhaps eccentric among biologists in not leaping immediately to that answer. I would add a combination of the following three answers: “Because wings wouldn’t be useful to them; because wings would be a handicap in their particular way of life; and because even if wings might be useful to them, the usefulness would be outweighed by the economic costs.” The fact that wings are not always a good thing is demonstrated by those animals whose ancestors used to have wings but who have given them up.” I have read Richard since his ‘meme’ theory book and greatly appreciate his contribution to the innovative thought and the popular conversation around evolution. I do find passages like the above a bit irksome in its anthropomorphism. And I find the general reaching for anthropomorphic language among evolutionary scientists attempting to find analogies that the average punter might understand, has made the education of the population in evolutionary theory, a bit stale and tainted with fiction. So, to be clear, there is no “wings wouldn’t be useful, wings would be a handicap, and definitely not outweighing economic costs, or wings are not always a good thing” except in that we as humans often mislead ourselves by using value or evaluative terms such as “usefulness”, “handicap”, 'economic cost" and “good”. Moving our human mindset for these e-value-ations to a clearer, this is what worked and how it came about, would be edifying. Indeed I am reluctant even to put a why on evolutionary outcomes because it hides the fact that evolution and nature as it is, came about as a flourishing in which 99% of mutations or variations are lost to species development, just didn’t work so didn’t propagate past even one generation. In otherwords, stuff just happens, and when certain stuff can react well with other stuff, more of that stuff gets made, then we have a flourishing of stuff all supporting each other, until something happens and the stuff just all dies. And then, if any substrate environment continues to exist that has the possibility for organic processes, more lively stuff will probably start to develop again. Richard did get to this point by the end of this excerpt for which I was much relieved.