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Ever since I was young and interested in science
fiction and in evolution, I often scoffed at the big-headed people that
were supposed to man flying saucers - why, I said, would billions of years
of evolution, a long series of random and chaotic events, have produced
creatures that were recognizably humanoid on another planet?
But recently I've been giving it a bit more
thought. You might be surprised
at how likely it is for an intelligent species to be at least vaguely humanoid...
We'll take it step by step.
First, we have to agree that the sort of life
under discussion would have developed in some sort of water environment
(not absolutely necessary, but it's hard to get the complex chemistry to
work in the atmosphere of a gas giant planet, and other possible liquids don't
dissolve things well enough to get an appropriate complex chemistry going - I wouldn't discount the possibility at all,
but we'll just avoid the long list of unknowns by sticking with
aqueous-based systems). You also need lots of energy input for high-level
biological organization, probably sunlight on an Earth-like
planet... Again, other energy sources are possible (our distant
ancestors may have organized using geothermal energy) but have limitations
that would probably keep life too simple.
First, on a pathway to intelligence, you're
going to have to go through nervous systems. That sort of
quick-response system gives
you some animalistic form of life. Intelligent plants are an
interesting science-fiction idea, but evolving them would be tricky -
animal-plant types could get you there, I suppose, but it's hard to see a
big advantage for intelligence if you can get most of your nutrients just
basking in the light.
Next, movable life forms (animals) that have a preferred movement direction
evolve a front end with most of the senses and processors there (an
evolutionary process called cephalization), and a bilaterally
symmetrical (with "matching" right-and-left-side structures) form behind it for efficient locomotion. Animals that
don't move this way shouldn't develop the central processors necessary for
intelligence. That gives us animals with a head end, complete with
brain and a lot of front-loaded sense organs, and pair-matched limbs...
Life may have evolved in water, but living in water is unlikely to lead to
what we consider intelligence in a science fiction universe - that is,
technology or advanced manipulation of tools. You could make a case for cephalopods
(octopus, etc.) being smart, and potentially highly intelligent, but
there probably are limitations to what sort of advanced technology could
be derived while living in a salt- water environment. Electricity as we
know it is pretty much out. Marine life would have many other
materials-based technological disadvantages as well. You may want to
look at whales as a form of intelligent life, but
they barely qualify as science-fiction "sentient life" (and
there are better explanations for their brain size than smarts). So we
need animals adapted to land and atmosphere, and they need...
Land animals need legs. How many legs? It seems like more legs could bear
more weight, but what you actually see in fossil history on Earth is a reduction in leg
numbers in groups like insects and spiders (whose construction materials
and organization - skeleton on the outside - limits
their potential size and, unless you're going for a hive-mind, their intelligence
levels too). Is four legs a good number? That's the most unpredictable aspect -
our fishy ancestors, and their first land-living descendants, had four, pretty much across the board, but
it's unclear whether that would be a functional preference rather than
luck-of-the-draw. Eventually, to get intelligent animals you need to get at least
one set of legs free of weight-bearing responsibility - this leads to the
manipulation abilities (hands) that, in humans, led to vast development of
our brain abilities after birth (being carried reduced immediate sensory
and coordination needs in infants and allowed their brains a longer time
to develop), as well as our being able to carry
tools around. Carrying the same tools around for a while puts a premium on design efficiency and
durability (technology), as
well as instructional communication - although early human communication probably had more
social underpinnings than technological ones (social organization, though,
seems like another "must have" in our evolving thinkers). Our
likely candidates for smarts would have internal skeletons (greater size possible, so
bigger brains) and jointed legs, a trait which shows up in wildly
different groups as a natural answer to the challenge of moving quickly
around on land. You could make a guess about joint number and limb
placement that would probably get you something similar to what you find
on our planet's animals.
What's on a land animal's head? The pertinent senses from way back when are
sight, sometimes in a flat facial plane to facilitate depth
perception (can you manipulate tools efficiently without depth
perception?), found often in predators and active tree-climbers; hearing, with binocular detectors well separated to localize sound (that
could be located someplace other than the head, though); taste somewhere
near the mouth (but in animals with a long history of hands, they could be
there), which would be on the head, and probably smell (a powerful
component of taste) in the vicinity. Neither of these last two is too well
served with bilateral structures, so something central is more likely. The
really complex level of communication skill you'd need for intelligence would probably be
at least somewhat sound-based, although visual (as in squid skin-pattern
shifting) is possible, and you could go with telepathic although it's hard
to support it from a physics standpoint (sort of - you can support pretty
much anything if you dig far enough into quantum mechanics, though).
What do we get? Something at least partly upright, with jointed limbs
matched right-to-left, some sort of grasping/manipulating hands and a head
probably moved more above than in front of the body. A couple of eyes
(single lens, which is a better system than multiple lenses [compound
eyes] if you've got the room), a mouth, some sort of nose, possibly ears.
Humanoid? Maybe. If velociraptors had had a chance to keep evolving, would
their intelligent descendants be humanoid? Depends on how you define
"humanoid."
Should intelligent, technological aliens be "Star Trek"-style
humanoid, like earth people with minor variations? Not without some religious implications, I would think. Could
they be humanoid within a modern TV budget? Definitely.
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