Krdytkyu

There are many tiny humanoids in fiction, the Arquilians of Men in Black, the Gargantians of Buzz Lightyear Star Command and a few others. This raises the question, is it possible for a humanoid species to evolve to be so small?

Let's try to stick to natural evolution only and no tiny machine sentient entities.

1. Can primates be very small and live an independent existence?

Answer: Yes, for example the Pygmy Marmoset. https://en.wikipedia.org/wiki/Pygmy_marmoset

2. Can humans be very small?

Answer: They can certainly be small. https://en.wikipedia.org/wiki/List_of_the_verified_shortest_people

NOTE - At this point I have to attend to real life so will have to continue this later.

There are two implicit questions here:

1. Are there any physical factors about humanoid bodies that prevent functioning at that scale.


2. Can a creature that small be intelligent

Mammals come in a range of sizes, all the way from tiny (the Etruscan Shrew weighs 1.8g) to huge (an African elephant can weigh 6 tons), so a human's fundamental biology seems like it shouldn't have issues. However, you will notice that all small animals tend to use all four limbs for motion. Even squirrels with relatively dexterous hands use them while running. I think this is because as you get smaller, terrain gets relatively larger. As a result, the smaller an animal is, the better it has to be at climbing, and at small scales this probably favours claws over gripping-fingers.

The other question is one of intelligence. Can a small creature be sapient? Well, this is an impossible question to answer really, because we can't really figure out what it is that makes humans different to animals from an intelligence perspective. Some thing that may offer clues is the brain-body-mass ratio. Man definitely falls near the upper end of that, and you can see a definite increase of "intelligence" as the brain mass increases. However, even animals with brains 5-6 times heavier than humans don't seem as intelligent. And on the other end of the scale, the Portia spider has a body 5mm long (and so a head that is extremely tiny), and yet it exhibits the ability to "hunt in ways that seem intelligent". This includes the ability to plan routes to prey that take it out of visual contact.

I have a theory that the physical form of an animal dictates it's intelligence. I think that (given an evolutionistic model), any creature with sufficiently dexterous manipulators, sufficient perception fidelity, and with the ability to communicate with others of it's species should be able to become intelligent given enough bootstrapping time. So if you had a miniature humanoid creature and left it for long enough, that theory states that the creature will become intelligent.

So in short: I can't see any reasons why it wouldn't be plausible.

I'm not sure how small we're talking, but take a look at chimpanzees.

Now if you had a chimpanzee become more intelligent (i.e. more synapses and more oxygen-rich blood flowing to the brain, as well as heat dispersion), for reasons such as gaining an advantage over other species or navigating complex and ever-changing environments, it would be quite imaginable.

The main issue I spot is heat dispersion, since the surface area is considerably small when compared to the volume of the head. Some of the heat may be transported through the blood, perhaps leading to large ears (such as in African elephants or desert foxes) or tongues (thing panting dogs) to dissipate the heat.

A more exotic solution might be to shape the skull in such a way as to increase the surface area, perhaps with deep wrinkles or folds, though this may come with structural integrity issues, and will not transport the heat in the center to the surface very quickly. It may also impede the room for the organs, perhaps even causing a split brain for a U-shaped skull.

Other than that I don't see a problem whatsoever.

EDIT: I'm completely wrong as pointed out in the comments, it's the larger the animal the harder it is to manage heat. Pity though, may have been interesting.