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I am writing a story about a man who survived a plane crash and found himself on a desert island after some time finds out that he got to another planet, and then there he meets a reasonable upright hyena with whom he comes into contact and begins to establish life together, preparing for winter.

Because of what, in the course of evolution, four-legged predators living in the savanna can move from exclusively quadropedal movement like all four-legged animals to biaidal like humans, but so that they still have the opportunity to move and hunt on four legs?

Hyenas have an average height of 160 cm — they are small compared to humans. In particular, our hyena is quite tall — 168 cm. It weighs about 65 kg. Overall, slightly less than the average person. The man himself is quite heavy — about 85 kg and 190 cm. He can easily pick it up and "transport" it. But at the same time, hyenas are more wiry than humans, and much stronger — it will not be difficult for her to lift a mass slightly exceeding her own weight and move it again.

Hyenas can run up to 30 km/h on two legs, while on four - up to 60 km / h. How long they can work depends on many factors, in particular temperature. So, at a temperature of +20 ° C, a hyena can run at maximum speed for no longer than twenty minutes, but at +5-10 it is already one hour, but this is the limit, because then her body reacts very weakly to cold and loads at the same time. Hyenas themselves usually run for no more than five, a maximum of ten minutes – during this time the hunt usually ends, so it becomes pointless to continue running regardless of the result, and then they sleep in a state of siesta until the end of the day. But in general hyenas are very hardy, no worse than a wolf, however, due to the fact that they live in a hot climate, they are capable of extremely powerful, but short-term work. So, Aisha with a rush of adrenaline can literally catch up with a deer and wring its neck or crush its spine with its jaw. When there are a lot of hyenas, each makes a maximum of one lunge and retreats, and this is enough for the victim to be incapacitated. Crush the victim's leg, and she will not run away, so when hunting hyenas, the main thing is to drive the prey and make one or two accurate and powerful bites. Tactics were changed only by the appearance of the throwing spear. Hyenas, like wolves, are able to move huge distances, but slowly – they take a long time to prepare for hunting or even ambush, often at a watering hole. But from the point of view of technological physical labor, a person undoubtedly wins because of the possibility of sweating.

Frank Thompson 4
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    In principle, it's always the same process: the changes that provide advantages tend to spread into population as they are inherited by offspring (or the genes are spread via other means). The changes are typically tiny, but in the long run they accumulate into larger ones. The exact evolutionary path of your hyenas is another question. There are plethora of ways it can happen, and no one can figure out the ultimate best solution to that problem. So, in the end, you can tell whatever story you want. – Jani Miettinen Oct 08 '23 at 12:24
  • However, why should they walk on two legs – what does it give them? – Frank Thompson 4 Oct 08 '23 at 12:46
  • Wolves and hyenas will not walk like us on two legs – they are predators who need to run on four, and such changes require an appropriate need and millions of years of evolution, which we do not have and what we do not need, because a quadrupedal can have more or less normal hands. – Frank Thompson 4 Oct 08 '23 at 12:47
  • This could provide some insights: https://en.wikipedia.org/wiki/Bipedalism – Jani Miettinen Oct 08 '23 at 12:47
  • Full-fledged vertical walking like humans will not help them in anything, it will require millions of years of evolution when they will already be intelligent and will make something with their paws, hands and teeth and graze cattle, and, probably, on the contrary, will worsen their ability to run on four legs, which is a priority for them: how can Aisha simultaneously is it normal and all day long for people to walk on two legs, and it is also very easy to walk and run like an ordinary terrestrial hyena on four, stretching up to sixty kilometers per hour (versatility is not easy)? – Frank Thompson 4 Oct 08 '23 at 12:47
  • Top predators (and hyenas on an island will be the top predator) do not have the evolutionary pressure to change. Humans developed bipedalism in response to being preyed upon. It gave us the ability to walk through the heat of the day when predators were asleep. – David R Oct 08 '23 at 14:23
  • "Evolution of quadriped to biped" is an often asked question here. Unless you are asking specifically for suicidal consideration for Earth's hyenas, this is a duplicate of on of the other questions. Even then, this has to be extremely similar to any thing else. –  Oct 08 '23 at 16:26
  • About half the questions in this search are very similar. –  Oct 08 '23 at 16:31
  • There is a very high chance that this is a duplicate of either Would intelligent life evolve any other body plan than humanoid? or Evolution of werewolves. It's not enough to be hyenas. Please read the two links and [edit] your post with an explanation for why they don't answer your question. Thanks. – JBH Oct 08 '23 at 22:51

2 Answers2

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For humans, it is suspected that they adapted to bipedalism (from knuckle walking; like a gorilla in a forest) as a result of climate change, that disfavored forests and jungles, and created vast grass plains.

Apes can already lift themselves up to two legs to see further, and some gorillas can walk a considerable distance (or for a considerable time) on two legs. However, it is not comfortable for them, because their pelvis is not adapted to this form of walking.

Even dogs can do this, I've seen dogs walk about a block "standing up" on just two legs. It's kind of a hopping walk, and easier for small dogs, but a proof that quadrupeds can do it.

On the savanna, however, very tall grass meant that the early apes transitioning from the forest couldn't see threats, prey or anything else around them while knuckle-walking, and had to "stand up" pretty much all the time.

For your hyena, I'd pose a similar evolutionary paradigm. Give the hyenas a bigger enemy, on the savannah, something that hunts hyenas. Big enough to see over the tall grass, big enough to be faster than them, big enough to kill and eat them. Much like lions on the savanna, for humans. But it can be any large carnivore, a huge bird of prey, a freakin' velociraptor type predator. The hyenas need to see it coming a mile away. And they develop intelligence, and their front paws evolve to better use tools, for the same reason humans did, because the velociraptor type predator that you invent is like a lion, a brute force killer that can be outsmarted.

If you want something to evolve (like intelligence in humans, or bipedalism, or tool making, or language), you need to invent a reason for that thing to be a trait that increase survival and/or the odds for reproduction. (Some things, like the peacock's tail, do not increase survival rates, but actually decrease them. However, for males a large symmetric tail is a sign of good health and nutrition, and gets selected by females, so while reducing the chances for survival, it increases the chances of peacock reproduction even more.)

I thought hyenas mostly scavenged. But in any case, your hyena's bipedalism, that preserves their ability to run and hunt on all fours, will take a special kind of pelvis to be comfortable and efficient in either positon. I wouldn't get into the details in fiction, I'd just have the "unusual pelvis configuration" mentioned at most, to cover that base for analytic readers (like me).

Amadeus
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  • The problem is that I do not know why these intelligent hyenas can develop erect walking, because in the case of the option you proposed with high predators, it would be enough to hunt in a pack, where one hyena would watch the horizon and, if anything, could give a sign to others. – Frank Thompson 4 Oct 08 '23 at 15:09
  • @JaniMiettinen Intelligence at the human level seems to be an exceedingly rare occurrence, just based on our empirical experience. In fact, one animal behavioral researcher I read says everything humans do, we see in animals. Verbal and Sign Language, planning, the ability to do arithmetic, the ability to process abstractions, a theory of other minds, etc. It is just that humans take it further than any animals. Something happened in humans that did not happen in millions of other species. I think the odds of two species with human level intelligence evolving separately is very near zero. – Amadeus Oct 08 '23 at 16:29
  • @JaniMiettinen You mentioned two species of intelligent animals, the "high predators" (I presume my velociraptor-like species that eats hyenas) and the "hyenas" themselves. My point is that this is a highly unlikely scenario, for two separate species to develop high intelligence simultaneously. – Amadeus Oct 08 '23 at 17:08
  • @JaniMiettinen Then you don't understand my last sentence. To an extent intelligence is a feedback loop, but there is a reason we don't have a 1000 species on Earth with human level intelligence! For the purpose of this specific question, we need hyenas with human level intelligence. (HLI) Yes, they probably gained that by being hunted by some animal, but the acquisition of HLI is so incredibly rare that is is extremely unlikely any species but the hyenas would evolve it. Thus "high predators hunting in packs and intelligent" is exceedingly unlikely to get the hyenas "in trouble". – Amadeus Oct 08 '23 at 17:15
  • @JaniMiettinen octopi, corvids, many apes, elephants, dolphins, yes. Many develop and use simple tools. None of them have invented even a simple flint knife, or a multipart tool, or armor. An elephant could easily carry a 50 pound club, and use it to fight the big cats that sometimes hunt them and manage to kill them. Yet they do not. Humans occupy a distinctly different plateau of intelligence. – Amadeus Oct 08 '23 at 17:22
  • @Jan Then you apparently misread my answer. I did not edit my answer, If I had an edited answer shows that it was edited, when and by whom, in-between the "Share Edit Follow Flag" at the bottom and the answer's author. The question I was answering, written by Frank Thompson 4, was also not edited. – Amadeus Oct 08 '23 at 22:19
  • ...and essentially those hyenas evolve into kobolds or "inu" type creatures - bipedal, intelligent, with distinct hands, but unable to run on fours. Alternative monkeys if you ask me, just out of dogs. – Vesper Oct 09 '23 at 06:50
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Short answer is they can't and won't

You can always hand-wave and say "and then there were walking hyenas" but it's not something I think can evolve.

Hyenas have a digit-grade stance, which means their skeleton is built to walk where our knuckles start. This is to make the skeleton springier and better for running. Primates, bears, raccoons, and a few other species are plantigrade which is generally more versatile for climbing, holding stuff, etc. but it's also usually slower for running. The ancestor of all carnivores appears to have been plantigrade (as seen in species from the family Miacidae, the earliest carnivores) and evolving into a digit grade stance seems to be a one-way street. Meaning, you can't evolve back into plantigrade (to the best of my knowledge).

My advice would be to hand-wave it or choose a species from the family of bears, raccoons, civets etc. that are plantigrade to evolve into your bipedal species. Some marsupials are plantigrade and also have thumbs so that could be fun to play with. I would personally choose the cuscus! https://en.wikipedia.org/wiki/Sulawesi_bear_cuscus

Whatever species you choose, you can say that they were arboreal or semi-arboreal and as the world got drier during the Quaternary (when ice ages started) and forests turned into savannas they traded their life in the trees for running along the ground. Also occasionally reaching to grab things that are high up is useful when your bipedal for fruits or any food.

Jacob Dembitzer
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