.......but why DOES flight occur so rarely for mammals?
I’m not the best person to ask this, but from my very surface knowledge of evolution and biology, there are two speculated reasons I’ve read about:
1) It’s expensive.
Not in the sense you may be thinking of - animals won’t be crashing the stock market anytime soon (much as we might want them to) but in order to survive, all animals must balance their expanded energy that they use for Super Special Animal Moves like Fly, Swim, Forage, Tackle, etc, against their intake of energy (eating things).
For example, to maintain its ability to be Huge and Strong, an African elephant must consume about 70,000 calories a DAY. But with their food source being what it is, in order to meet this need, they need to graze for 12-16 hours of that day.
Flight requires quite a bit of energy as well, and requires more of it the larger you are. Therefore, in order to achieve powered flight (not gliding, which evolves much more frequently) an animal would need to be able to support its energy needs AND balance that with its size/weight.
Bats, the only mammals currently capable of true flight, digest things HELLA FAST and have thinner, more flexible bones. (Birds have hollow ones, which helps with the weight issue as well.) This means that they are more capable of easily balancing their necessary caloric intake against the energy they need to fly.
2) For many mammals, it’s unnecessary.
Evolution isn’t a conscious process - it has no goal in mind. Things which CAN happen - based on the resources and time available to a group of organisms - MAY happen.
But most often, evolution takes place due to availability or opportunity.
Say, for example, a food source.
Let’s take a look at a simple representation of an ecosystem with available food sources.
If the ecosystem has food in 3 niches (places)
in the sky
then what would happen if we plopped down some hungry Organic Things into it?
Well, if they can all only walk on land, they’re going to eat all the food and die of starvation pretty fast. Especially if one of the organisms is naturally better at it - has some sort of advantage that makes it easier for them to get the specific type of food.
BUT, if they all go after different TYPES of food, they could potentially stay alive as a species if they randomly evolve/develop an advantage for ANOTHER type of food.
Or sometimes they don’t/can’t.
And depending on what the needs are, some organisms will have more of a pressure to evolve specialized adaptations like flight.
But those pressures are not always present - especially for mammals, which have been, historically, pretty good at filling out other, non-air niches.
Plus evolving flight after you’ve already got other advantages is unlikely, given that you may have to take some evolutionary moonwalks to get to the correct stat set.
Anyway I feel like I got carried away with the yellow blobby things, but I hope that helps out... somewhat.
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