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JWFokker · 04-13-2005, 07:57 PM

Land animals don't benefit much from having more than four legs. It's not faster or more agile. But if an animal developed two arms and four legs, while having limbs to manipulate objects with rather than use it's mouth would be beneficial, it would likely have poor balance and mobility would be hindered, rendering it unable to compete with it's simpler four legged predecessors. Imagine a dog with four legs and two arms. It's torso would have to be lengthened or develop another body segment so that there would be a place for the arms without having too much weight in the front. It's just wouldn't happen naturally. If you were to engineer such an animal, if you took into account the weight balancing and such, you'd probably have a very successful animal.

But evolution doesn't just happen. Even the fastest evolution occurs over more than a million years (like the development of eyes) and it a progression of a trait. Taking the development of eyes for example, this happened some 400+ million years ago. The first 'eyes' were no better than light sensitive spots on the creature giving it a basic sense of direction, which over millions of generations developed into something more and more sophisticated until it reached what we now call an eye. Before this, all life was blind and moved and fed and killed other lifeforms based upon touch. Once the eye was developed, lifeforms with this feature were able to actively search for food and navigate much more efficiently. Within the first few generations, a mutation must be beneficial to be successful or it will be replaced with something that IS useful. You'll notice that nearly all successful life on the planet has eyes, or is at least light sensitive, because it is a particularly useful trait. You may also notice that there are no land animals with gills or flippers (discounting frogs and platypus because they are predominantly water based). These traits aren't useful on land. So they died out. So for an animal to mutate and develop a third set of limbs, there would have to be some benefit to it if it is to become successful. Because there would be a long period of time where the third set of limbs would not be beneficial, or would even be detrimental, it's unlikely a four limbed animal would develop a third set or limbs. It's far more likely that a six limbed creature, like an ant or other insect, would evolve into a more advanced creature, something more along the lines that you described. But insects are mostly genectially stagnant, so this isn't particularly likely.

04-13-2005, 07:57 PM	#25
JWFokker Cooling Savant Join Date: May 2004 Location: Kingston, NY Posts: 269	Land animals don't benefit much from having more than four legs. It's not faster or more agile. But if an animal developed two arms and four legs, while having limbs to manipulate objects with rather than use it's mouth would be beneficial, it would likely have poor balance and mobility would be hindered, rendering it unable to compete with it's simpler four legged predecessors. Imagine a dog with four legs and two arms. It's torso would have to be lengthened or develop another body segment so that there would be a place for the arms without having too much weight in the front. It's just wouldn't happen naturally. If you were to engineer such an animal, if you took into account the weight balancing and such, you'd probably have a very successful animal. But evolution doesn't just happen. Even the fastest evolution occurs over more than a million years (like the development of eyes) and it a progression of a trait. Taking the development of eyes for example, this happened some 400+ million years ago. The first 'eyes' were no better than light sensitive spots on the creature giving it a basic sense of direction, which over millions of generations developed into something more and more sophisticated until it reached what we now call an eye. Before this, all life was blind and moved and fed and killed other lifeforms based upon touch. Once the eye was developed, lifeforms with this feature were able to actively search for food and navigate much more efficiently. Within the first few generations, a mutation must be beneficial to be successful or it will be replaced with something that IS useful. You'll notice that nearly all successful life on the planet has eyes, or is at least light sensitive, because it is a particularly useful trait. You may also notice that there are no land animals with gills or flippers (discounting frogs and platypus because they are predominantly water based). These traits aren't useful on land. So they died out. So for an animal to mutate and develop a third set of limbs, there would have to be some benefit to it if it is to become successful. Because there would be a long period of time where the third set of limbs would not be beneficial, or would even be detrimental, it's unlikely a four limbed animal would develop a third set or limbs. It's far more likely that a six limbed creature, like an ant or other insect, would evolve into a more advanced creature, something more along the lines that you described. But insects are mostly genectially stagnant, so this isn't particularly likely.