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I have a species of ambush predators that are going to be sentient space-farers one day. But to get them on that path I need them to evolve hands, which will lead to tools, and so on.

They come from a world of wide open grasslands, mountainous regions and canyons, no large forests.

The predators themselves are built roughly like tigers, they lack a tail, and instead they have several long flat antenna growing off their heads that they use to entangle prey after jumping onto it in order to bring it down.

What can I introduce to their grassland environment to help them develop dexterous grasping hands?

I can give more information on both the world and predators as needed.

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    $\begingroup$ Couldn't you just make the antennas prehensile? That would have a practical use in their original role, and would have the necessary dexterity for tool use. Admittedly, they'd lose the leverage of having arms, but if they have strong necks, those could suffice in a pinch. $\endgroup$ – user70585 Mar 14 '18 at 21:55
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    $\begingroup$ Normally for this kind of question I'd put an answer that would summarise down to 'make them arboreal' but you've already stated that forests are not big on your planet. Truthfully, the one thing you can introduce to your grassland to create hands would be trees. It's the ability to use a dexterous hand to grip branches and climb that makes a hand more useful in evolution before tool building is possible. $\endgroup$ – Tim B II Mar 14 '18 at 22:27
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    $\begingroup$ Worth noting is that evolution is typically "Things showed up that were useful and stuck around" rather than "Something was needed so showed up" - Putting the same situation towards a group of animals and letting them evolve will produce different results each time dependent on the group of animals. Crows are smart, and use tools, but have no "Hands" to speak of. $\endgroup$ – Andon Mar 14 '18 at 23:25
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    $\begingroup$ I'm with @TimBII, let's add to it a reason to be preferred. Cats love climbing trees, but let's give them a predator that can also climb trees. One day, the genetic die roll leads to a cat with slightly longer and more flexible digits... the beginnings of a hand. Because this cat has improved dexterity and control, it can avoid the predator better than its siblings and survives. It breeds, and two of its offspring have the genetic "improvement." Soon they all have it, and someone develops this weird thing called a knuckle, and it happens all over again. $\endgroup$ – JBH Mar 15 '18 at 0:16
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As others have mentioned, the basic food web needs to change. Felines pouncing on game don't really require hands so much as claws to hold and pin. Reasons this setup could require hands:

  1. The feline is (slowly) forced towards omnivory and/or out of the apex predator spot. Specifically, food that requires preparation or overcoming some passive barrier of some kind. If you can just get the nutrients from biting something, the big brains and dexterous hands won't develop. Look at scavengers like rats or raccoons.
  2. Bipedality becomes useful in addition to another mitigating factor. The grasses become too tall and thick, or the prey evolves some way to totally avoid detection from ground-level might point towards bipedality, but that bipedality might only need tiny T-rex arms. You'd need some reason to use those now-freed-from-walking digits. Complex social requirements? A longer onboarding process for young? Taking down prey suddenly requires eye-gouging ala Three Stooges?
  3. Tool use. Prey starts using burrows that require you to use a stick to get them out. Lean times has the felines start eating bugs like termites where obtaining them at a distance is the best way to avoid being bitten by the whole mound. Prey develops some armor that outdoes the felines' bite strength or teeth sharpness, requiring the use of a rock to break it open.
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    $\begingroup$ I'm marking this as the best answer because it's offering some options to drive them where I want to go, rather than just saying it can't happen. I'll probably be making a follow-up question inspired by these points. $\endgroup$ – Giga Mar 16 '18 at 16:22
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What would it take to make this “Big cat” species evolve hands?

There would have to be an advantage to having hands. Say... if they dwelled in the trees. Not just climbing up big trees and laying on big lower branches for napping and scanning, but actually living up there, jumping from branch to branch and tree to tree, where opposable thumbs really useful for grasping.

Of course, there aren't dense forests (where hands are needed for leaping -- and grasping) from tree to tree in the grasslands. That's why there aren't any hand-grasping creatures except man in the African Savannah or the American Great Plains. But where did man evolve from? The trees.

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Polydaktyly (having additional toes on each foot, including opposing "thumbs") is a mutation that occurs naturally in cats and it is speculated that polydaktyly was evolutionary advantageous for ship cats (it is frequent in cat populations founded by ship cats at many places of the world).

So it is not too far fetched that a big cat evolves some kind of "hand".

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You already mentioned that they jump on their prey and then bring it down.

Have you ever tried to grapple with someone without using your thumbs? It's hard. Even with the antennticles, that might be your evolutionary pressure right there.

Also, my house cat "grips" things between her paws all the time. And at least here on Earth in the real world, it's easy for most species to adapt extra digits when needed.

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  • $\begingroup$ +1. But what is an antennticle? $\endgroup$ – Renan Mar 15 '18 at 14:27
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    $\begingroup$ @Rennan Giga described the cats as having "...long flat antenna growing off their heads that they use to entangle prey after jumping onto it in order to bring it down." Since grappling and entangling are usually what tentacles do, antenna + tentacles = antennticles. Should have spelled it antenntacles, but hey, it's out there in the world now. $\endgroup$ – KernelOfChaos Mar 15 '18 at 19:26
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The hands would appear when the brain requires them. To have a need for hands, the animal would need to handle small objects. Thus, I can suggest several ways for you.

First, obvious, is a gradual decline of prey that you can leap upon, with the increase of prey that you can just pick up. Cats gradually turn from carnivores to insectivores, may be rodent eaters. Then hands will evolve for the ease of picking, the use of tools in form of sticks for digging, so on.

Another, more fantastic. Introduce a plant to your world, that has fruits that are deadly poisonous to touch. It may be like a chestnut with deadly spikes, or it may contain the poison inside and the hit makes it to burst open. You carnivores learned to pick those objects and hurl them at their prey. More agile ones are better hunters, so agility with small items increase.

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    $\begingroup$ Cats are rodent eaters, but don't have hands. $\endgroup$ – RonJohn Mar 15 '18 at 11:31
  • $\begingroup$ A typical prey of home cat is 1/4 - 1/8 of its size. Did you ever watch a cat trying to catch a pillbug? Cat wishes it had hands at these moments. $\endgroup$ – Barafu Albino Mar 15 '18 at 12:53
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    $\begingroup$ They do. Each time they need a pair of hands they meow and a pair of hands appears. $\endgroup$ – Censored to protect the guilty Mar 15 '18 at 14:29
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    $\begingroup$ The hands would appear when the brain requires them. A quick skimming over The Darwin Awards defeats that argument (just kidding). $\endgroup$ – Renan Mar 15 '18 at 14:31

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