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In my world there human-animal hybrids. My protagonist is a snow leopard-human girl (outwards looks almost completely human, except for the tail). These hybrids have been created through experiments, so there is no evolution in play.

So I can also play around with sci-fi-ish elements (and/or magic). What would be ways for a cat-human hybrid to achieve more agility?

For example, from what I understand, because the spine has to support the skull, it kinda loses flexibility. If these hybrids would be given implants, could it give some flexibility back?

Additional informations:

  • These hybrids vary greatly, a few walk on all fours, others don't, others are digitigrade and so on
  • I'm mostly interested in my main character. She looks and moves like a human, unlike most hybrids she grew up with humans and only at 13 she began to learn about her hybrid side (story takes place 10 years later)
  • Her animal characteristics are tail, eyes and claws, and she's short. And I would like to have also muscles like felines (if it has advantages)
  • I want her to still fit in with humans, but be able to move with more agility, for example climb, jump, sprint...
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    $\begingroup$ Could you edit to add any constraints you want to stipulate? For example, your comment about the spine implies that your human-leopard hybrids need to walk upright. Do they have to broadly fit in human-centric society -- posture, clothing, daily routine, etc? How different can they be besides the tail? $\endgroup$ – Monica Cellio Apr 21 at 20:13
  • $\begingroup$ define cat like agility, What thing do cats do that you think a primate of the same size could not? most of the agility advantages cats have are due to size. humans have big agility advantages over cats in the arms and legs, a human can scratch their own back for one thing. – John 5 mins ago $\endgroup$ – John Apr 21 at 23:32
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    $\begingroup$ Tail helps for balance, especially in the air. Humans have very low density muscles - it helps us swim otherwise we'd sink like other primates. So higher density muscles would be nice for added strength and speed without adding any bulk. $\endgroup$ – MParm Apr 22 at 0:51
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    $\begingroup$ @MParm Human muscle density is the same as other animals, we have different muscle recruitment not different muscles. Also chimps can swim, they don't naturally, but they can learn too, much like people can. humans float better becasue we have more fat in our body. $\endgroup$ – John Apr 22 at 1:40
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    $\begingroup$ "Cat-like agility" would be a downgrade for a human. Cats can crawl, walk, run and jump and that's it. We can do all that: and in addition we can swim, we can dive, we can brachiate (which only us monkeys can do), we can hop on one foot, we can move feet first, we can stand erect for a long time, we can kick and we can punch; we have much better motor control; we can move our fingers individually; our forelimbs have very much wider possibilities of movement, etc. etc. $\endgroup$ – AlexP Apr 22 at 20:11
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Interesting question! I have some basic and anatomical considerations that might be of help to you.

Since the hybrids are created using technology (gene editing and so forth), your genewizard scientechs need to do things like these:

  • Ensure that the balance centers of her brain derive from cat genes
  • Derive her balance, movement and recovery instincts from her cat forebears
  • Derive her tail, its musculature and its nervous apparatus from the cat, but see below for specific anatomical considerations
  • Apart from genetic manipulation, you'll want to make sure her natural abilities and instincts are well trained.

You don't need implants in the spine, you'd need to remove bone, if anything. The human frame is not built to move like a cat. If you want a catgirl that looks mostly human and has a basically human body, you're going to have to accept some trade-offs. I think if you do the above three points, she'll be considerably more agile by nature than any non-hybrid.

One thing I'd point out, since your catgirl has a tail, is that almost every artist that draws furries gets the tail wrong, from a human-beast hybrid anatomical perspective. Just be aware that a functional and anatomically correct furrygirl won't look like the vast majority of furries you see in art.

Take a look at this furry girl here (cat-human hybrid by mrpersonperson of dA --- Don't worry, totally SFW!) :

enter image description here

And now compare the human skeleton:

enter image description here

with the cat skeleton:

enter image description here

noting the differences between the pelvis and placement of the tail in all three. Notice that the human tail (yeah, we have tails, but they're entirely internal) curves inward and how the gluteus maximus curves outward. Notice how mrpersonperson stuck his furry's tail way up high in the lumbar region of her back. More important than supporting the skull, the spine has to weld the pelvis together to support the whole body! That means she will have no sacrum, no bone to hold the two halves of her pelvis together. She'll collapse, most likely, and certainly not be able to walk let alone leap about gracefully as a cat!

I point this out to bring your focus to the tail. The cat uses its tail quite a lot for balance and agility. Your catgirl will not really be able to do this with a basically human body. This is where her feline tail will end up having to be:

enter image description here

Its bones and musculature will partially push her glutes off to either side, probably giving her a weird gait and certainly making it difficult for her to sit like a human.

Mrpersonperson should have had his furrygirl's tail emerge approximately where her g-string disappears between her glutes.

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    $\begingroup$ If we look at the human tail bone, it may be possible that the tail bone in hybrid humans is curved outwards and is more horizontal than it is is regular humans, maybe even creating an almost ‘S’ shape. This would allow for the tail to protrude outwards much higher than your last image shows, perhaps being as high as it is in the first image (though, if that is whats happening, the angle is slightly off). $\endgroup$ – Liam Morris - Reinstate Monica Apr 21 at 20:51
  • $\begingroup$ @LiamMorris --- My issue isn't with the tail per se, just noting for the OP's information where the tail comes out on a human body. It's not where most artists put it! $\endgroup$ – elemtilas Apr 21 at 23:28
  • $\begingroup$ primate of the same size are already far more flexible and agile than cats, What advantage to you think you will get from their balance center, the one big advantage cats have (the tail) is already being added. $\endgroup$ – John Apr 21 at 23:28
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    $\begingroup$ @John --- Tail by itself is useless. Humans don't know what to do with them. A furry hybrid will need the genes to not only grow a tail, but also grow the musculature & nervous network to make it function, plus the base instinct set to use it naturally. She will also have to train her mind & body how to work the thing consciously. Since it's a given that she's got a tail, it might as well be put to good catlike use, rather than the limp and useless human alternative. $\endgroup$ – elemtilas Apr 22 at 1:14
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    $\begingroup$ @elemtilas humans don't know what to do with arms and leg either, they have to learn to use them. Cat instincts won't help a creature with a human body anyway. $\endgroup$ – John Apr 22 at 1:24
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You don't have to do anything, humans are already more flexible than cats

You have already given her the only advantages you can, if she has a tail and claws she can do anything a cat of her size could and likely a lot more, agility wise. the advantage house cats have is size, smaller animals can move faster. Cats are not more flexible than humans, humans are actually really flexible if they put any effort into it, far more than cats. Humans evolved from primates they are amazing climbers and jumpers and can contort themselves in ways cats could only dream of, like everything in hte below image.

enter image description here

The only other tangible advantage you could give them is better muscle recruitment, which is why large cats can jump so high, but that will cost her fine motor control. So she can jump 18ft but she can't write her own name, not a great tradeoff. this is more strength than agility anyway.

Keeping her body mass small will help, mass is the biggest limiting factor for agility.

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  • $\begingroup$ This is the correct answer. Humans are apes, primates, we are way more agile than cats. Our limbs have much wider movement abilities, our motor control is much finer. $\endgroup$ – AlexP Apr 22 at 20:05
  • $\begingroup$ OK, and now let's compare flexibility in the majority of cats and humans. I think I can do the 2 standing poses in your image and that's it. Then again, if I also got up at 3AM to work out by randomly running through the house, I might be able to do more... $\endgroup$ – R. Schmitz Apr 23 at 22:17
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    $\begingroup$ @R.Schmitz scratch your own bum, cats can't do that. humans have discoupled shoulders and rolling hip joints which allows for a huge range of motion. $\endgroup$ – John Apr 23 at 23:14
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Scale body size down and metabolism / perceptual speed up.

Small animals with high metabolic rates (e.g. songbirds, chipmunks) process visual stimuli faster than larger, slower metabolizing animals do. It makes sense. What is the point of perceiving what is happening if you are too slow to do anything about it? But if you are able to move fast you have to be able to process sensory stimuli fast or you are literally flying blind. Move your cat woman's size down and metabolism and perceptual speed up.

From: Metabolic rate and body size are linked with perception of temporal information Kevin Healy et al

In a broader context, it might be expected that manoeuvrability, a vital component of an individual’s ability to respond to the environment, may be one of the main factors determining whether it is necessary to invest in costly temporal information processing. Manoeuvrability, as defined by the ability to change body position or orientation, generally scales negatively with body mass. This negative scaling emerges primarily through the increased inertia and decreased limb stroke rate associated with large body size …

These arguments show that, owing to the laws of physics, larger animals physically respond less quickly to a stimulus. Hence we expect selection against costly investment in sensory systems with unnecessarily high temporal resolution in large animals, as information on such timescales can no longer be utilized effectively. This may explain why larger vertebrates, along with those with low metabolic rates, had lower temporal resolution in our study.

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    $\begingroup$ Cats have twice the resting heart rate of humans. Which means they live half as long and twice as fast. That's where their 'agility' comes from, aside from the obvious corporeal differences. $\endgroup$ – Mazura Apr 21 at 22:53
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Smaller and thinner is always more agile.

Less fat and smaller internal organs also help - at the cost of endurance and ability to use low-energy foods.

Bones should be lightweight and not too easy to break - so fill them with some air, like a bird's bones. Even if that means broken bones require longer treatments.

Some of the brain could go down into the spine (as with birds again) - especially anything related to motoric abilities. Improves reflexes, allows for a smaller head without reducing intelligence and strengthens the spine without adding unnecessary weight.

Stealing photosynthesis from the plants (ideally black, brown or red ones, as green is not a cat-like color) helps to recover strength while resting, even if it only makes a small percentage for a warm-blooded being.

Some animals like Kangurus can 'spring-load' their muscles. This allows jumping around without using a lot of energy.

The larger the frame, the more the bones need to support the muscles - make bones near important muscles across joints extend a little bit for a better angle the muscles can use. Muscles can overlap by splitting the extension into a Y-shape on one side, which also stabilises the joint. Only works for joints limited to one direction, like knees or elbows.

A muscle along the back could help go quickly from a crouch to a jump, or from absorbing a landing on two feet to jumping again. Useful as your 'cat' will usually not use all four paws for movement, I assume.

The hind legs can be a little short for a human - allows switching to running on all fours if needed, for extra-fast sprints. Here, the strengthened back muscle will also add to the speed.

A relatively long neck will help move between upright and quadropedal movement, and also be good for fast jabs - like a snake or a bird.

4 or 6 small boobs are better than 2 large mammaries. However, if you want your cat-woman to be sexy for humans, use the place well - fat, water and oxygen storage, for energy, dry spells and diving, respectively. Similar to some animals expanding their throat, your cat woman could then use her mammaries to signal attraction.

Make your tigress cheat a little - shoes with a blade spring each, an elastic climbing rope with knots for easier climbing (shoes should have a small gap between toe and other digits, to make use of this), knee and elbow protectors for wilder maneuvering, a flight suit for jumping from large heights and other such accessories.

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I agree with pretty much every answer on here so far since agility is many different things, but there is one other factor to consider that I think will make a bigger difference than any of them. When a cat stands at rest, their legs are bent. But humans normally stand with legs straight. Our straight design gives us a longer stride allowing us to run faster and support ourselves better with our inferior number of legs, but it comes with some hefty trade-offs.

Any time a human wants to react to something, we must first bend our legs/arms in, then respond. A big part of why we perceive cats as so much more agile than us is that they have no delay. With legs already bent they can go straight from a restful stance to a lunge. The bent design also means they can allocate their muscles differently. While we need our legs to be strong in all directions for support and versatility, a cat has most of its hind-leg muscles allocated for pushing backward with a strong heave, and just enough for bringing forward to repeat. This is why they can push forward so much harder than us.

So to answer the question, give your cat-girl bent legs, and have her move more like a monkey than a person. She should be able to stand up well enough to do people things with her hands, but if she wants to run, she drops to all fours, because on 2 feet, she'd be a slower and more easily worn out than her straight legged friends.

enter image description here

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    $\begingroup$ This answer probably could be improved with actual pictures of cats standing up since that is something they do. I've never seen one walk that way before, but it would still probably be a good (and cute) reference. $\endgroup$ – Muuski Apr 22 at 19:58
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    $\begingroup$ Important reference material: youtu.be/UR6IpfAsHQ8 $\endgroup$ – Nosajimiki Apr 23 at 6:47
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Have muscles like felids

Human muscles are heavily optimized for endurance, but the price is they are quite weak for their size. Felids in contrast have muscles optimized for strength and peak power, which gives them much more agility, but at the cost of endurance. That's why even the most active cat will fall off after at most 20 minutes of play, while humans can with a bit of training run for 10 hours straight.

With muscles optimized for strength and human body plan, you'll get something closer to an ape, but they are just as agile as felids, if not more. You can put retractable claws on the legs for traction control. On hands they are unfortunately incompatible with useful fingers—the claws are in place of nails and are retracted by curling the fingers up—but if she's running on two like human, she does not need them there anyway.

Tail is not particularly relevant. elemtilas is correct about its position, but it's mostly cosmetic—bobcats and manx cats are no less agile and neither are old world monkeys. It may be useful for small attitude corrections in jump or fall, but the main corrections are done by bending the back and rotating limbs.

You do want to keep the weight down, but the stronger muscles will need correspondingly strong skeleton, so the body build will probably come up as rather robust. But felids are not particularly slender either; they are strong and powerful.

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