To quote u/PhaiLLuRRe -
I don't know why it is that these things bother me---it just makes me picture a seven year old first discovering things about an animal and, having no context about the subject, ranting about how stupid they are. I get it's a joke, but people take it as an actual, educational joke like it's a man yelling at the sea, and that's just wrong. Furthermore, these things have an actual impact on discussions about conservation efforts---If every time Koalas get brought up, someone posts this copypasta, that means it's seriously shaping public opinion about the animal and their supposed lack of importance.
Speaking of stupidity and food, one of the likely reasons for their primitive brains is the fact that additionally to being poisonous, eucalyptus leaves (the only thing they eat) have almost no nutritional value. They can't afford the extra energy to think, they sleep more than 80% of their fucking lives.
Non-ecologists always talk this way, and the problem is you’re looking at this backwards.
An entire continent is covered with Eucalyptus trees. They suck the moisture out of the entire surrounding area and use allelopathy to ensure that most of what’s beneath them is just bare red dust. No animal is making use of them——they have virtually no herbivore predator. A niche is empty. Then inevitably, natural selection fills that niche by creating an animal which can eat Eucalyptus leaves. Of course, it takes great sacrifice for it to be able to do so——it certainly can’t expend much energy on costly things. Isn’t it a good thing that a niche is being filled?
Koalas are no exception, when their teeth erode down to nothing, they resolve the situation by starving to death
This applies to all herbivores, because the wild is not a grocery store—where meat is just sitting next to celery.
Herbivores gradually wear their teeth down—carnivores fracture their teeth, and break their bones in attempting to take down prey.
They have one of the smallest brain to body ratios of any mammal
It's pretty typical of herbivores, and is higher than many, many species. According to Ashwell (2008), their encephalisation quotient is 0.5288 +/- 0.051. Higher than comparable marsupials like the wombat (~0.52), some possums (~0.468), cuscus (~0.462) and even some wallabies are <0.5. According to wiki, rabbits are also around 0.4, and they're placental mammals.
additionally - their brains are smooth. A brain is folded to increase the surface area for neurons.
Again, this is not unique to koalas. Brain folds (gyri) are not present in rodents, which we consider to be incredibly intelligent for their size.
If you present a koala with leaves plucked from a branch, laid on a flat surface, the koala will not recognise it as food.
If you present a human with a random piece of meat, they will not recognise it as food (hopefully). Fresh leaves might be important for koala digestion, especially since their gut flora is clearly important for the digestion of Eucalyptus. It might make sense not to screw with that gut flora by eating decaying leaves.
Because eucalyptus leaves hold such little nutritional value, koalas have to ferment the leaves in their guts for days on end. Unlike their brains, they have the largest hind gut to body ratio of any mammal.
That's an extremely weird reason to dislike an animal. But whilst we're talking about their digestion, let's discuss their poop. It's delightful. It smells like a Eucalyptus drop!
Being mammals, koalas raise their joeys on milk (admittedly, one of the lowest milk yields to body ratio... There's a trend here).
Marsupial milk is incredibly complex and much more interesting than any placentals. This is because they raise their offspring essentially from an embryo, and the milk needs to adapt to the changing needs of a growing fetus. And yeah, of course the yield is low; at one point they are feeding an animal that is half a gram!
When the young joey needs to transition from rich, nourishing substances like milk, to eucalyptus (a plant that seems to be making it abundantly clear that it doesn't want to be eaten), it finds it does not have the necessary gut flora to digest the leaves. To remedy this, the young joey begins nuzzling its mother's anus until she leaks a little diarrhoea (actually fecal pap, slightly less digested), which he then proceeds to slurp on. This partially digested plant matter gives him just what he needs to start developing his digestive system.
Humans probably do this, we just likely do it during childbirth. You know how women often shit during contractions? There is evidence to suggest that this innoculates a baby with her gut flora. A child born via cesarian has significantly different gut flora for the first six months of life than a child born vaginally.
Of course, he may not even have needed to bother nuzzling his mother. She may have been suffering from incontinence. Why? Because koalas are riddled with chlamydia. In some areas the infection rate is 80% or higher.
Chlamydia was introduced to their populations by humans. We introduced a novel disease that they have very little immunity to, and is a major contributor to their possible extinction. Do you hate Native Americans because they were killed by smallpox and influenza?
This statistic isn't helped by the fact that one of the few other activities koalas will spend their precious energy on is rape. Despite being seasonal breeders, males seem to either not know or care, and will simply overpower a female regardless of whether she is ovulating. If she fights back, he may drag them both out of the tree,
Almost every animal does this.
which brings us full circle back to the brain: Koalas have a higher than average quantity of cerebrospinal fluid in their brains. This is to protect their brains from injury... should they fall from a tree. An animal so thick it has its own little built in special ed helmet. I fucking hate them.
Errmmm.. They have protection against falling from a tree, which they spend 99% of their life in? Yeah... That's a stupid adaptation.