How evolution explain two legs, two hands, two eyes
Plz explain this to me.How evolution explains the simultaneous development of two similar body parts?Why Two eyes and not one?Science claims that a special neuron was developed some time long ago by a microorganism and that sun hit that neuron and at some point an eye was created.But why two eyes?Two neurons existed?Why not three neurons?Why no creature has one three or five eyes?
Praeses
Re: How evolution explain two legs, two hands, two eyes
Embryos split symetrically, it's more efficient that way.
The whole problem with the world is that fools and fanatics are so certain of themselves, but wiser people are full of doubts.
-Betrand Russell
Re: How evolution explain two legs, two hands, two eyes
So this means we should have two noses also?Originally Posted by Himster
Comes Rei Militaris
Re: How evolution explain two legs, two hands, two eyes
We have two nostrils.
One thing is for certain: the more profoundly baffled you have been in your life, the more open your mind becomes to new ideas.
-Neil deGrasse Tyson
Let's think the unthinkable, let's do the undoable. Let us prepare to grapple with the ineffable itself, and see if we may not eff it after all.
Tribunus
Re: How evolution explain two legs, two hands, two eyes
Praeses
Re: How evolution explain two legs, two hands, two eyes
If Dara O'Brian wasn't an atheist I'd probably call him a prophet, he's so cool........and big, he's like 20 feet tall.
The whole problem with the world is that fools and fanatics are so certain of themselves, but wiser people are full of doubts.
-Betrand Russell
Dux Limitis
Re: How evolution explain two legs, two hands, two eyes
Bilateral symetery, we wouldn't really function too well if both halves were totally different from each other.
The wheel is spinning, but the hamster is dead.
Comes Limitis
Re: How evolution explain two legs, two hands, two eyes
Some animals have eight eyes...
Spiders...
No?
Okay.
Do you know how many eyes a fly has? Me neither. Eleventy-six and I stopped counting.
Also I nice gif. Very effective at distracting me from your words and thoughts and such.
Last edited by Col. Tartleton; October 08, 2010 at 02:50 PM.
Dux Limitis
Re: How evolution explain two legs, two hands, two eyes
You can chop a spider in half as well it still has two sides the same. Something like a starfish you cn cut into four idenical segements, a jellyfish can be cut anyway you want.
The wheel is spinning, but the hamster is dead.
Re: How evolution explain two legs, two hands, two eyes
So this means that two eyes, two ears etc were developed by luck and not because they give the organism a better chance to control his area.Well sounds reasonable to me.Now explain to me why hands, legs, eyes are symmetrical?I would like to have a bigger right hand compared to a left.It sounds reasonable.After all most people use the right hand so inevitably the right hand would grow bigger
Dux Limitis
Re: How evolution explain two legs, two hands, two eyes
Massive claw on one side tiny claw on the other it can happen, but why would we need a massive hand on one side for?
The wheel is spinning, but the hamster is dead.
Comes Limitis
Re: How evolution explain two legs, two hands, two eyes
Crimson Fists is for fighting!
Massive claw on one side tiny claw on the other it can happen, but why would we need a massive hand on one side for?
Re: How evolution explain two legs, two hands, two eyes
Well i would expect to have as an organism the possibility to grow a bigger right hand.I have the possibility to see my neck growing 5 meters but i dont have the possibility to see my right hand grow. Isnt it unfair?
Massive claw on one side tiny claw on the other it can happen, but why would we need a massive hand on one side for?
Civis
Re: How evolution explain two legs, two hands, two eyes
The number of limbs we have was determined very early, by some of the earliest vertebrates that moved onto land. Organisms sticking to symmetry was developed even earlier. They're basic characteristics, not easily changed by evolution if it would be beneficial. That said, the numbers of organs we have make a lot of sense.
4 limbs - 1 doesn't really allow an organism to move easily on land, 2 let's it crawl but that's not very efficient, 3 is unstable plus asymmetrical, 4 is the lowest number of limbs that allows an organism to move across most kinds of terrains. 6 would work too, but it would be very inefficient.
2 eyes allow us to see depth
2 ears help with determining where a sound came from
2 longs are less vulnerable than one big one
Etc.
Triggering
Re: How evolution explain two legs, two hands, two eyes
"When I die, I want to die peacefully in my sleep, like Fidel Castro, not screaming in terror, like his victims."
My shameful truth.
Tribunus
Re: How evolution explain two legs, two hands, two eyes
The reason we are symetrical is because terrestial mammal's common ancestor was a long symetrical slug in the cambrian era. There were other non symetrical creatures but most of them died out. Key with this sea slug was the ability to undulate it's back (later becoming a back bone) and even spacing of it's parts. The origin of eyes comes from wanting to see. There's many creatures with all numbers of eyes but it becomes a major computational challenge to focus so many eyes at once, something that evolution has difficultly producing quickly. Having two eyes allows a creature to use binocular cues to see much clearer and judge much better the environment it is in. We can only guess what trinocular cues look like because as far as I know it's only evolved once in shrimp that live on the bottom of the ocean, we use binocular vision.
The simplest explanation of this is because of our undulating back bone. As we undulate it means that a single eye would be blind to a large area of field of view. While this doesn't necessarily mean the animal can't exist (indeed animals like that did exist) it just means that predatory animals with two eyes have an advantage against these animals much like shoot fish in a barrel. Our ancestors evolved two eyes so they could see on both sides of them. As animals diversified from this common ancestor some evolved into carnivores, their eyes needed to face forward to judge distance better and to focus on a single object. On the other hand prey animals needed to be able to see nearly completely 360 degrees. Prey animal's senses are no where near as specific as predator's are but they provide superior ability at detecting the slightest differences in their environment.
As we know two eyes aren't necessarily the best and for a long time arthropods held a distinct advantage in the animal kingdom possessing compound eyes making them the top predators for millions of years. Some scorpion ancestors grew up to a meter or more in size. Our common ancestor at the time merely excelled at one thing, escaping. You can understand why such a strategy proved to, over time provide that genetic lineage with the greatest chance at survival. Our eyes that we used as fish served us very well and there were only slight developments that our terrestial ancestors made to them. Bigger eyes, more cones, more rods, better clarity and better brains all increased our ancestors ability to see to the point where arthropods quickly lost out to amphibians. Arthropods also hit an evolutionary brick wall, they could no longer get larger, in fact due to their extremely primitive breathing and circulatory systems arthropods never again returned to the size they were as oxygen levels plummeted. Our base genetics proved not necessarily to be more adaptable, but better suited to the development of a brain and complex bodies. Quickly the armor, venoms, and silks that had lead arthropods to the top became moot points.
To return back to why we have pairs of legs and what not we must look again at our common ancestors. The things about genetics is it's very difficult to add something like a new point for legs or arms in a complex animal. It's much easier to work with base code that is already permissible for such a tool. Our primitive ancestors had this in their basic limbs. From a more primitive perspective we evolved from a six (seven including the body) sectioned animal. Section that later would specify into our arms, legs, heads, and tails.
Our fingers are much easier to alter than limbs but even they take millions of years to get rid of. Hooves, and fins still clearly look like hands after 50 million years of mammalian evolution. This is because mammalian common ancestor's were essentially rodents that survived by being too small, too quick and more adaptable than the dinosaurs. These mammals notably had five toes owing this to the common ancestor between themselves and reptiles. Many reptiles had various organizations of toes and this variance is still present in many birds. The common ancestor on the other hand had five toes. Sometime after the split this common ancestor evolved a four chambered heart. This heart is essential, among other innovations, to the mammal's dominance. Although the reptiles went on to improve their lungs independently and bird lungs work roughly 3x as good as ours do mechanically.
Initially birds did have the advantage and after the era of the dinosaurs was 10-14 million years of terror bird dominance (ancestors of the ostrich and emu except larger and meaner), but these terror birds became big and slow. Eventually this paved the way for a major upset as receding shore lines allowed a small social mammal to emigrate across the planet. This mammal was omnivorous as it's rats ancestors were but more importantly it took the social habits of the rats and harnessed it for gathering food. A technique that hadn't been heavily employed since the dinosaurs. Just as the raptors easily dispatched larger dinosaurs the mammals easily dispatched the large slow birds. The ostrich, having evolved on the african plains proved to be quick enough to survive till today. Australia was cut off at this point preventing the Emu from going extinct, most other surviving terror bird descendent's were hunted to extinction by early humans.
All of these animals however probably had dichromatic sight. As in they had blue cones and green cones to see with. Only one species of tree shrew seemed to evolve the ability to see in trichromatic sight. It did this through an accidental copy of the same genetics for dichromatic sight, essentially we have two copies of the dichromatic sight genes (which in themselves are two copies of the monochromatic sight genes) which for whatever reason (the chemical transition from DNA to protein is waay to complex to understand currently) produces a third cone cell in our eyes, or Red. The descendents went on to possess some of the best sight of any mammal, the improved vision allowed it to live an arboreal existence in the trees protected from predators and provided for by the trees. These animals became known as monkeys and apes, eventually hominids split from these lines evolving into us.
In summary, our commonalities with other animals speak of the fact that our common ancestor had evolved these traits already. Meaning that our hands are not so different than the hands of any other mammal. We know this is true which means mammals are very likely to be very related. DNA proves this to be true. It's difficult to evolve new traits in evolution and it takes eons. There's a reason why insects have evolved so many interesting solutions to the planet, they've had a lot more time to diversify than the mammals have. We on the other hand were catapulted in a relatively short amount of time to absolute dominance. Intelligence, our social structure and our ability to dexterously use tools has given us something by total coincidence that evolution has failed (as far as we know) to create ever before, if any evolutionary event in our prehistory had been different we could've never appeared, or perhaps appeared sooner. There's only one evolutionary path you can take to get to humans. There's billions if not trillions of evolutionary paths on this planet. Some animals share more of the journey in common than others before diverging off.
Every physical event that happens changes those paths regardless of what life on this planet wants. Life adapts to those changes because that's what life does. If you want to understand why life adapts you must understand the abiotic chemistry of abiogensis, specially why RNA and DNA mutates. If you want evidence that these things appear naturally: http://www.popsci.com/science/articl...new-study-says
As far as we know all you really need for these chemicals to appear is a star system, an active volcano and temperatures which allow the chemicals to keep existing.
Last edited by Elfdude; October 08, 2010 at 05:12 PM.
Civitate
Re: How evolution explain two legs, two hands, two eyes
Tell me, martian, if man were designed then why did God give men nipples, and why do humans have an appendix at all?
(I know the scientific answers to both, merely answering martains thinly veiled attempt at questioning the validity of evolution with a straight response)
Re: How evolution explain two legs, two hands, two eyes
LOL did i said that we are handmade?I just realise that Life has some traits that look similar to a scientific experiment.You have your DNA, you have the ability to evolve and as time passes more and more complicated organisms emergeTell me, martian, if man were designed then why did God give men nipples, and why do humans have an appendix at all?
(I know the scientific answers to both, merely answering martains thinly veiled attempt at questioning the validity of evolution with a straight response
Campidoctor
Re: How evolution explain two legs, two hands, two eyes
As been said. We have 2 eyes to be able to see depth, 2 ears to hear in stereo and 4 limbs because that's the most effecient way to travel by land.
Tribunus
Re: How evolution explain two legs, two hands, two eyes
Well not necessarily, there's many other options life ended up on this path because of competition and eliminations that happened relatively early in it's history. Many cambrian era creatures look completely unrecognizable.
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