Chapter Text
Rocky was curious about Human biology.
That didn't narrow it down.
He was curious about their evolutionary biology.
Rocky had five limbs, Grace had four. All of Rocky's limbs could be used as hands and feet while Grace's limbs could only do one or the other.
It was a strange design. Very inconvenient. They had already encountered the problem of what would happen when Grace needed a third hand but couldn't have them. What about if he needed more legs? Bipedal--the word for what Grace was--design was awful for running. It seemed awful for most things, in Rocky's opinion, when you looked at their proportions.
Legs seemed like highly inefficient locomotion tools, but Rocky had a theory that was more Grace's fault than Human evolution's fault. Rocky has never tripped over his own limbs before.
Grace explained that it had its purposes and benefits, and that Rocky shouldn't be too harsh to judge the evolution of a species that was lightyears away on an entirely different planet. Rocky was going to keep judging, but he stayed quiet as he listened to Grace explain how bipedalism was more energy efficient, gave Humans greater fields of vision, and resulted in better respiration which opened up the pathway to brain growth.
So by evolving into something incredibly flawed they made themselves smarter.
How stupid. But interesting all the same.
But their design raised a lot more questions for Rocky. After Grace showed him what other organisms on Earth looked like he realized that Humans had very long legs. He also learned that in Humans their leg sizes could vary, not just in width but in length. Eridian leg length always remained perfectly proportionate to an eridian's carapace size.
He asked Grace if he was one of the Humans who had long legs, to which he responded that he was pretty leggy.
Rocky's not sure why he decided to answer it like that.
When asked why Humans were so 'leggy', Grace responded with that it was how they evolved to hunt.
That intrigued Rocky. Why wouldn't it? While Grace's hunting skills were highly questionable--Rocky reiterates that he has never once tripped over his own limbs--he was still a member of his planet's 'Top Dog' species. Why them referring to themselves as a lower lifeform was a compliment Rocky would never understand, but the point still stood.
Eridians were ambush predators, not pursuit predators. As great as five legs were, they did happen to be less energy efficient, so chasing after prey was a taxing hunting strategy. The most common eridian hunting strategy was to camouflage oneself as a rock and wait till prey got close. Then, when it's guard was down, they'd spring out and lift up their hindest leg to deliver a swift but punishing attack that would kill the prey almost instantly most times.
Like a mantis shrimp, Grace had said. Or a 'blunt force damage scorpion', whatever that meant.
One method included holding it down and blowing steam out of their radiators on the prey to cook it to death. Another involved gripping the prey tight and bashing it around till it died. A bit brutal, but eridians evolved to have durable carapaces and dense body weight so they couldn't be batted away or stopped easily.
Humans obviously weren't built for such tactics. So what were they built for, then?
Grace explained to him that Humans were persistence hunters.
"Stupid name. All hunting persistent unless hunter gives up," Rocky interrupted.
"Okay, fine, endurance hunters. Now don't interrupt," Grace scolded.
To hunt, Humans would just follow the prey, doing a mix of walking and running to conserve energy while making sure it didn't escape. They'd use the low endurance of their prey to their advantage, knowing that it'd have to take breaks each time it sprinted. And they'd simply just keep following it until those breaks got shorter and shorter until eventually, the prey became too exhausted to keep up its escape attempt, and when it was down the Humans would kill it.
Long distance running, it was called, that Humans evolved perfectly for. They were cursorial beings.
One of their muscles, the tendon, was longer than it was in other species which made it better for locomotion on flat ground. Their feet had arches that provided "spring action" which reduced the energy expended while running. The same went for many other structures inside them. Compared to other Earth animals they had a significant lack of hair covering them which helped them cool down in the heat unlike their prey.
The grossest advantage of all, however, was sweating. Humans already leaked so many disgusting fluids, and did so way more frequently than eridians were known to do. Sweat was one of those fluids and was unfortunately great for thermoregulation.
Rocky would be willing to look past every evolutionary trait in Humans that he insulted if they'd be willing to try and evolve into something less leaky. They could stay blobby if they insisted, just not leaky.
All in all, their evolution made sense when Grace explained it and, despite Rocky's complaining throughout, did seem very beneficial. He could say all he wanted about inefficient Human design because whether or not it was true by the end of the day, they were still the leading animals of their planet. So obviously, it worked.
But Rocky still had questions.
"Why animals not just fight back, question?"
Grace put a hand to his chin in thought, and Rocky mimicked it over his carapace's "face."
"For starters, we hunt in packs, so the animal was likely outnumbered and knew fighting would be dangerous."
"What if animal bigger than Human? It still not fight back, question?"
"Well the trick with bigger animals was to keep them scared. Most animals, including the big ones, were prey animals. So they'd choose flight over fight. We'd use traps and weapons--like projectiles--on them to keep them injured and afraid. Then we'd follow them so insistently they didn't have any time to rest and gain confidence in the idea of fighting back, assuming that kind of thing crossed their minds. It wasn't a perfect system--plenty of people died during these hunts--but it worked well enough for us to have done it enough times that historians could find evidence of these hunts."
"And how humans not lose prey, question?"
Grace shrugged. "Because humans can jog for hours, but these animals could only run for a few minutes. Sure, they were faster, but they didn't have the stamina to do it long enough to escape. It also didn't help that they were likely injured from a trap or ambush before running. These hunts would last a few hours, usually. But if the animal did get far enough away we'd probably just track them by following their footprints or blood trail."
"Amaze. Human hunt so good, but now trip over own shoelaces. What go wrong, question?"
"Wh- hey! Nothing went wrong, we're all fine!" Grace sputtered indignantly. "Shoelaces just do that sometimes."
Rocky chortled. The noise sounded like a ton of chirping birds. "Grace would make awful hunter. Eridians still capable, but Humans not."
"Okay, so I've tripped a few times. That doesn't make me incapable. I bike! And exercise! I've never hunted but I wouldn't be, like, horrible at it. I could actually be a lot more capable than most people."
Rocky continued to laugh in the Human's face even as he crossed his arms and huffed. "Prove it."
"Prove it?"
"Yes. When we get to Erid, prove it. Grace hunt Rocky."
"Fine, I will!"
"Grace will fail."
"I will not."
"We see," Rocky replied in a teasing voice.