Convergent evolution with aliens.

I had wrote this up a long time ago and posted it, but i liked the thought and saved it in a file, so why not repost. I'll make a blog post of it too.







Convergent evolution in the universe.


I think, and im a minority in this typically, and also a layman so i am not trying to say i am more intelligent than anybody else when i say this, it is just my personal speculation,
That bipedalism with 4 limbs might be more common than some think, and that the humanoid form might be itself pretty common.
This will be long winded....

note. I am fully aware i am basing this on one example, earth, and that that lends itself to inherent bias from viewing one successful example.

Point one, bisectional symmetry.
Bisectional symmetry seams to be extremely efficient at achieving the neccisary actions to development, if we were based on one singular form, one blob, (one leg, one eye one ear etc etc) This makes many functions difficult. One eye does not compute depth perception and environmental dimension very well at all, even if you could spend optimal biological resources on making one super powerful eyeball, it would likely require more computation in the brain, thus more brain matter and/or energy usage to calculate the neccisary three dimensional space at a distance, because the dataset it receives (what you see) would lack dimensional context and would have to be internally calculated within the brain with the lower quality "data". Would also limit field of vision without making the eye take up an extreme amount of space to gain that field, which would leave that one very important organ open to horrible injury, and also reduced its capacity for fine focus, as it would be built for wide view over pinpoint, constructed to take in and compute a wider scope of information rather than calculate finer points, which would naturally have its disadvantages.
Threading a needle for such a creature for example would be a gargantuan undertaking.

One free appendage (arm) Should be pretty obvious when it comes to disadvantage, carrying while still manipulating other things, or getting one thing to interact with another etc etc you get the idea.
A trisected species, at first thought, more limbs, more stuff the better right?
Sure,  3 eyes in varying position, extremely wide field of view that could overlap for at least some depth perception and calculating 3d space,
3 legs, extremely stable locomotion able to move omnidirectionally with extreme ease.

(though bisectional animals, like on earth, achieve this easily by simply adding a new pair of limbs when needed, without a third portion of the brain needing to be added to support it, by the way)

3 arms, well, seams obvious right? 3 limbs free for manipulation, pfft seams a straight forward plus on the face of it.
But heres an issue with having 3 of everything, or being trisectional as a creature, this typically means dedicated computational locations in the computational matter, as in, your brain gets carved into thirds as well.
The fine motions of all three body sections require independent computation to handle their entirely different angles, especially when used in unison. All the muscle groups are in 3, all the organs are made to support 3, and the brain is working the greater workload of perpetually operating 3 entire sets of all of this organisms musculature, external features and extremities.
To operate EACH OF these sections at performance, and to build them at comparable performance  to a bisectional species, requires either an entire third more resources to remain on par, (in conjunction with a brain, which is an extremely hungry organ throughout life, doing comparative calculations through 3 independent sections to work them in conjunction. That makes for an extremely hungry bit of grey matter)
or to remain resource efficient, to have each section of those 3 that much more below par, less strong, less dexterous, comparatively less in size, less complex, whatever or whatever combination solves the issue of finite resource management and investment.
Having 3 eyes and the resource and computational requirements and extra bit of complexity in the brain having to communicate between its sections,
Just to gain the benefits of another 3rd eye of complexity on par or surpassing a  bisectional species 2,
Is yet another situation of requiring more resource and more computational power, when with just two you already achieved depth perception and the ability to compute three dimensional space,  so you are getting nowhere near the leg up Two is over one, benefit it may be.
It becomes a situation of diminishing of return,
When you could just spend those resources on two, REALLY REALLY GOOD eyes far more efficiently while achieving all neccisary functional baselines.
(think of it as designing your improved car to have a bigger engine, over designing it to have 2 engines, thus wasting space, duplicating complicated components etc, silly and not worth it and likely to require design issues that would result in diminishing returns, as previously mentioned, theres a reason sports cars dont just "add another engine", they improve the one they got)
So, in my humble opinion, my money is on it that Bisectional symmetry ALWAYS wins out over unisectional (unidirectional? idk) and   trisectional, and bisectional would drive trisectional into extinction in mere moments.
I think a bisectional invasive species would murder a trisectional ecosystem like the juggernaut running through rice paper walls.

Second point. Being bipedal with just 4 limbs.
Note, this one i feel is far, FAR FAR more likely to have deviations than creatures with trisectional formats. Im pretty solid in my expectation on everything being binary just out of efficiency sake. However 4 legs, at the end of the day, is a lot easier to make like each other and operate similarly and in conjunction than 3, one reason being 2 limbs or one limb, or six, on one half of a symmetrical body plan, can all be dedicated to one half of the brain portion dedicated to the function of those limbs, and only has to communicate in conjunction with one other half that controls 1, 2 or six limbs. Lending to that binary efficiency i was suggesting, given that they would both also be operating extremely similarly with less concern needed on total amount of neccisary angle capability in every limb.
However, the more you add, even if you can sort of standardize things better in this fashion, it still does ADD to computational needs, and thus resource needs. As well as the resource needs to upkeep those limbs themselves.
One of the reasons it is speculated we have the large brains we have for example, has a lot to do with the reason we have the shortest guts of all the apes.
Once our food (through developing omnivorous and cooking) became more varied and plentiful and digestible, (comparatively)
our guts shrank, which are also relatively expensive organs, as far as calories and other bio resources are concerned,
And we were able to dedicate those resources to our big ol super powered brains.  
This has also been found in some experiments i read years ago in selectively breeding fish for intelligence, by breeding those that finished mazes the quickest.
Their guts shrank, and their grey matter increased slightly. (given we could give them regular high amounts of food to make that possible for them).
So, Even as bisectional creatures, if you have numerous limbs, and all the supportive expensive components etc to support such a situation, (which includes more gut and brain dedication)
you require prohibitively more resource to support your system.
Thus, somewhat incentivizing a standard bipedal, two arm, two eye format for intelligent, technologically developing species.
Bipedal two arm form seams to, logically, have the most resource efficient blueprint, require the least amount of complexity neccisary to achieve all the basic environmental manipulation requirements,
To leave the most room (resourcefully) for the most likelihood to develop the neccisary brain power to be a technological species to begin with.

That is my story and i am sticking to it. lol.  That is the reason i am on team bipedal humanoids are everywhere.
Though likely far far far more different still than a simple star trek makeup job lol.
At least, i think its a matter of probability.
All the others are possibilities, and the universe is huge, thus, naturally, they have a good chance regardless,
I just happen to think the humanoid -ish but still very different from sci-fi tv shows form, is, in my opinion, probably extremely common,
And our form is probably not at all that special.
Many argue that it is anthropomorphic bias to assume other things are like us in this circumstance void of any connecting variables, you know, because their aliens.
I think it is just as viable to argue it is a bias to assume we are specifically special in our layout plan, and we may find out that its pretty run of the mill, as a system that is simplest for acheiving the neccissary goals.