Worldbuilding Stack Exchange is a question and answer site for writers/artists using science, geography and culture to construct imaginary worlds and settings. It only takes a minute to sign up.
Sign up to join this community
I'm writing a fictional story where non-primate mammals (and marsupials) evolved into different species of humanoids which roamed the earth.
In my world humanoids have evolved from animals such as bears , sloths and koalas including extinct animals such as Chalicotheres.
I'm wondering what evolutionary pressures could lead to the rise of such species.
Feasible
Primates evolved from a non-primate precursor, according to scientists, around 65 million years ago. So, there's nothing preventing the body structure of humanoids from arising given the right set of influences into a humanoid shape. The real question is why humans are human shaped. And the answer is intelligence.
Humans were designed with intelligence in mind. Being bipedal with thin but flexible fingers isn't an advantage unless you can do something better with the arms than if they were feet, like use and make simple tools or manipulate the environment to your advantage. Bears, for instance, derive an advantage from having four powerful limbs for movement, so if you want to have them become a humanoid, you need to give them a reason to use arms - and that's intelligence.
Evolution is a combination of random mutation and natural selection.
In our case, we exist because one of our ancestors had a mutation that caused the lumbar curve, i.e. where the lower spine curves the wrong way. That allowed standing and walking upright, which made it easy to see over tall grasses (a relatively recent development itself on an evolutionary scale) and use hands for carrying tools or weapons instead of walking, which in turn drove increased intelligence to better make/use said tools and weapons, all of which were huge selection benefits. Many other, lesser mutations refined that new form over time into what we are now, but that was the key.
Our primate ancestors were a bit smarter than other mammals, but nothing else really set them apart—or does so today, if you exclude us. If the same mutation happened in other mammals, you could easily get other bipeds, and they would likely evolve higher intelligence as a result just like we did. Convergent evolution to where they all appeared "humanoid" probably depends on how strictly you define the term.
So there’s according to Wikipedia 12 theories on why humans became bipedal, I remember there being more.
Anyways here’s a nice explanation for reasons to give your species human-like bipedalism: https://en.m.wikipedia.org/wiki/Bipedalism#Evolution_of_human_bipedalism
The problem you’re gonna run in to is that a lot of these problems we might have evolved towards bipedalism to fix are just things primates sorta suck at but other animals have better solutions for, like defense or travel, or they’re things that require a ton of specialized primate abilities to make into a good solution (like we were good at reaching for branches. Which may work for koalas but not sheep).
The one thing I could see working is introducing a very deadly predator in the food chain that’s proportionally more intimidated by large-sized creatures. It is a cheap way to make yourself appear significantly bigger.
Also based on that picture your animal has fingers, low facial prognathism, a butt, ability to use tools, non-rhiperian nose, and maybe a chin and maybe permanently enlarged breasts which are all pretty unusual physical traits it’ll take a lot more working to evolve if you wanna use them.
