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I'm trying to design a mammal that lives in trees. I'd like its hands to be good for climbing, but not good for using tools.

What aspects of the hand would make it good for climbing and not good for tool use?

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Lots of creatures climb, few creatures create and regularly use tools. Fewer still if you want human level dexterity in the hands.

Options

  • Hooves. Goats are amazing climbers on mountains...less so in trees but just an example.
  • Spider monkey hands, they don't have thumbs, they use their digits to hook around tree limbs.
  • Cat paws (as mentioned by Tim) I would look specifically at Jaguars. They spend a whole lot of time in trees.
  • Rodent paws (as mentioned by Aify)
  • Bear paws, sun and black bears are pretty darn good climbers

So the common themes here are.

  1. No opposable thumbs. This makes tool use more difficult and would increase wear on a tool, a firm grip is key for not stripping a screwdriver head for example.

  2. Claws. They are sharp. They break things.

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    $\begingroup$ As it happens, the ability to curl the little fingers independent of the others is almost as important as an opposable thumb. Try holding a tool if you have to curl all your fingers the same amount. $\endgroup$ – WhatRoughBeast May 23 '16 at 22:14
  • $\begingroup$ Goats climb trees surprisingly well $\endgroup$ – Separatrix May 24 '16 at 9:39
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The first thing that come to my mind is a Sloth. Just think of trying to use any tool with claws 4 inches long. Then think of trying to climb with grappling hooks!

Their specialised hands and feet have long, curved claws to allow them to hang upside down from branches without effort. They usually eat, sleep, and even give birth hanging from limbs. They sometimes remain hanging from branches after death even if shot from below by humans.

https://en.wikipedia.org/wiki/Sloth

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All you have to do is look into nature.

Geckos use setae in order to stick to surfaces, and if your hands have setae it would allow the creature to climb smooth surfaces easily (perhaps really large trees with smooth bark?).

But climbing can't just be generalized to smooth surfaces, and you mention trees - so what other aspects can help improve this? Well, snakes can climb trees. Snakes get their friction from their scales, which could also damage tools, so this counts for double points!

But whenever I think of climbing trees, I think of squirrels. Have you ever noticed how damn fast they move up them? I'd use their paw design - 4 longish fingers with claws on the end, with no opposable thumbs. Turns out, opposable thumbs are pretty important for using tools.

The verdict? Use a combination of natures finest. Style your mammals hands after squirrel paws, but also give them some scales and perhaps setae on the finger tips.

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  • $\begingroup$ Most climbing rodents really. Racoons are good climbers, so are quite a few weasels and some porcupines actually. $\endgroup$ – James May 23 '16 at 21:03
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    $\begingroup$ If someone showed up at the construction site with setae on their 'hands', I'd start to worry about my job security real quick. "Hey, why can't you keep up with Sticky? See, look, he can use seven screwdrivers at a time." $\endgroup$ – Mazura May 24 '16 at 2:09
  • $\begingroup$ @Mazura well I mean, I don't see how setae will help you use seven screwdrivers whatsoever - especially since it's not possible to rotate your fingers separately of each other in their own joints... $\endgroup$ – Aify May 24 '16 at 3:04
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    $\begingroup$ My point is that setae would be an asset, not a hindrance (usually). Mr. Sticky could hold nails, one (or more?) in each finger; I'd still have to use my mouth to hold the extras. $\endgroup$ – Mazura May 24 '16 at 3:57
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Have it use the cat design rather than the monkey design for climbing.

In other words rather than grasping/manipulating hands it has more simple paws with claws that it uses to grab into the bark of trees rather than hands it uses to grasp branches.

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  • $\begingroup$ I don't know that I would qualify paws as simple Mr Tim. They may not be human features but they are masterpieces of natural selection. Retractable claws to keep them sharp, padded for stealth, rough for climbing...oh and they can tear the throat out of virtually anything...so that's good...unless you've angered a wild cat recently. $\endgroup$ – James May 23 '16 at 21:02
  • $\begingroup$ They are simple in their utility in terms of fine manipulation. Tool manufacture and usage. Well evolved for their purpose I agree. $\endgroup$ – Tim B May 23 '16 at 21:17
  • $\begingroup$ Mainly just giving you a hard time... :) $\endgroup$ – James May 23 '16 at 21:40
  • $\begingroup$ @James you just reminded me of the time when I was a teen and a girl convinced me to try to pick up a wild kitten that was in the road. In the space of about 1.5 seconds my hand got more thoroughly shredded than I could have imagined was possible... *shudder* $\endgroup$ – Dan Henderson May 25 '16 at 14:04
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It's not the hand, but the brain

The ability to use tools effectively comes from the brain's ability to adopt this dead unfeeling extension as part of its body image.

A paw designed for swinging from branches or climbing or otherwise grasping in general might seem to make a perfectly good hand: if it can grasp a branch and hang on with enough force to support his own body weight, certainly then he can grasp the handle of an axe, right?

But, even with the grasping ability, he can't actually use an axe because his brain doesn't have the circuitry to make it function as an extension of his arm. It takes a great deal of practice to hit anything and the skill only works on that "trick" and doesn't generalize.

Note that I'm not referring to other aspects of intelligence. These creatures many have complex social interactions with politics and schemes, remember vast territories of resources and what signs indicate what to expect of the world around them. But using tools is a particular brain feature, and one we take for granted.

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  • $\begingroup$ I'm sure it doesn't take long for a dumb animal to realise he can pick up a thigh bone and smack his love rival over the head with it, despite what the monoliths say. That said, birds are adept tool users using only their beaks. $\endgroup$ – gbjbaanb May 24 '16 at 15:20
  • $\begingroup$ Some birds use tools. The New Calidonian Crow in particular is showing adaptations for tool usage. My pet pionus OTOH has a hooked beak which isn't good at manipulating things, and zygodactyl talons which are. He has flown off with my carving knives and has taken and opened my folding pocket knife, but the screwdriver alludes him. $\endgroup$ – JDługosz May 24 '16 at 17:59
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Bad for tools? Just take away the thumbs.

Good for climbing is very open-ended, as the other answers have showed with plenty examples. Here is a fun one:

Hands with lots of tiny retractable claws all over the palms

You put your hand against vertical rock, and any cracks will get filled with your little palm-claws, giving you heaps of purchase. These claws would give a world of pain when you slap someone, too!

A downside is a slimy surface would be impossible to climb, but you can use that as part of the ups/downs of the system.

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Give it sloth hands.

enter image description here

Big curved claws, useful for climbing and hanging from trees but useless for tool use.

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