How The Nocturnal Bottleneck and Nipples Make Us Human
Almost every post here considers what humans do have, really. It’s a little tiring; realistically every world has its harsh environments and vicious species and a sophont to match. We probably wouldn’t be unique for our adaptability or our persistence or even adrenaline
But our evolution is fucked up as hell, to put it lightly.
Mammals went through what’s been dubbed the nocturnal bottleneck essentially since the start of the mesozoic right up until the Cretaceous ended the archosaur’s exclusive hold over the daylight. We lost a lot of things from every mammal spending most of its time in either a cramped, suffocating burrow or scrounging around in the faint hours of nighttime. Our blood cells lost their nuclei to hold more oxygen while we spent time deep underground, we lost protections against ultraviolet rays in our skin and eyes, we can’t even repair our own DNA using the light of the sun. Most aliens probably wouldn’t have such traits unless their evolution followed a very similar path to ours. They’d be able to see ultraviolet and wouldn’t have to worry about sunburn and all the wonderful privileges essentially all fish, birds, amphibians, and reptiles enjoy as we speak.
There’s also what we gained from spending so much time in the dark.
Brown fat is only found in mammals, it’s a special type of fat which bear cells with several oil droplets and are utterly jammed with mitochondria. This lets it make heat, a lot of it, fast. We don’t even need to shiver to induce this heat generation from brown adipose tissue - factor in our downright hyperactive mitochondria, and we can warm up quickly. Sure, it doesn’t have too much use in adult humans, but it keeps our infants warm and still provides a little boost the whole run we have in this universe.
Unless aliens also went through a time where their small ancestors had to face cold nights, they’d have to produce heat the old fashioned way when chilled. Aliens might have to shiver the whole time they’re in a cold room while the human watches in confusion, quite literally unshaken, and wonders if the room is a lot colder than the thermostat set to 60 says. The aliens stare at their companion in confusion, it’s just a normal temperature to shiver at after all, how is the human sitting so still?
Our small ancestors spending all their time out foraging at night is also why we have such a good sense of touch, smell, and hearing. They were more important senses than vision (we’re lucky to have even redeveloped basic color vision, frankly) at the time and place and simply ended up continuing to serve us well. Birds and reptiles rarely have acute senses of smell and the latter especially are lucky to have acute hearing, and birds rarely have impeccable hearing themselves either. Our skin is free of scales and honed to sensitivity, and our external ears and complicated ear bones provide an immense range of hearing (from 20 all the way to 17,000 hertz!).
Aliens might not be able to pin down the chirp of a cricket or the light click of a lock being picked. The human might be the only one on board a ship that can pick out the finer sounds of the engine’s constant thrum and know the critical difference between when everything is fine and when something is wrong. The human could probably pick out the sounds of an approaching enemy’s careless footsteps - they’re only as light enough for *them* to stop hearing them, after all - and be the one to see the horrified expression (well, more on that later) on their face when we get the drop on them in spite of their perceived stealth.
But perhaps the most versatile, convoluted, amazing, and utterly unique trait we have is right on your face this instant. Lips.
Lips in most animals are a simple seal to hold in the mouth’s moisture and protect the teeth, even if they’re supple they’re NEVER muscular except in mammals, and we have only one thing to thank for it; milk and nipples. Lips evolved exclusively to allow babies to suckle, it required a vacuum to be created in the mouth, and with no other animal having anything like a nipple it never happened in other animals. Many animals make milk, to be frank, but no other animal has nipples.
Your cheeks and lips are a marvel among tetrapods, no other animal can suck like mammals can. Aliens wouldn’t have straws or even be able to sip from the edge of a glass, they’d have to have a proboscis or simply tilt the whole thing back. Aliens likely won’t have woodwind instruments or balloons you can blow into. We take so much about our lips for granted. Hell, our muscular faces are vital for expressions, we’re probably absolute facial contortionists among a cast of creatures with mandibles and beaks and expressionless scaly maws. Aliens might find us ridiculously easy to read, if anything, compared to their own kind (all the better to deceive them) - or perhaps they’d find us hard to decipher anyways, with our lack of color-changing skin or erectable crests of bright feathers. Baring teeth might not be seen as a sign of aggression in most of the universe, smiling would be all too distinctly human.
Perhaps with how infectious we are sometimes, that’s what we’d contribute to the universe; others might have to make do with opening their mouths just enough to show their teeth or splaying their innumerable mouthparts with just the right curve, but perhaps we’d teach the galaxy to smile, one ally at a time.
Wouldn’t that be amazing?
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