Because there were open ecological niches on land which had less competition for resources than back in the water.
Well, your answer is nice, however it shows the evolutionist contortionism needed to justify the theory. My statement was in response to the following:
For one thing, "we" would not all have evolved into the same thing because we don't all live in the same environment.
So explain how if fish are adapted to this nice watery environment they need to go through the trouble of growing legs and all the other changes necessary to become earth inhabiting creatures. Seems to me there would be a lot better (and easier ways) of becoming more dominant in the environment they already knew.
Also, if they lived in the sea and could not walk and stuff, how did they know there was an 'empty niche' on land? Who told them? Does natural selection have esp??????????????
Ridiculous. Sorry, I don't mean to beat up on gore3000, but he's fighting a fight that's not even happening. Why do the creationists act like they're being confronted by those that subscribe to evolution when the evolutionists simply dismiss creationism as junk science based in religion and really not even worth the time and trouble to address?
Well, your answer is nice, however it shows the evolutionist contortionism needed to justify the theory.
No, it's a direct answer to your question, based on well-known and universally accepted biological principles. If it seems contorted to you, let me know which parts you're having trouble with and I'll explain them in more detail for you.
So explain how if fish are adapted to this nice watery environment they need to go through the trouble of growing legs and all the other changes necessary to become earth inhabiting creatures.
Your phrase "go through the trouble" shows a great misunderstanding of how evolution works. Would you like me to point you towards some good introductory material?
But in partial answer to your question, see my post #27. The development of amphibious capabilities may have first been in response to other sorts of survival pressures, and only later put to use to expand into unoccupied land-based ecological niches.
Furthermore, there is good evidence that legs and lungs at least got their starts because they were useful in some entirely underwater circumstances. Leg-like structures are used by some bottom-dwelling fish to help them "run" along the sea floor efficiently, and primitive lungs are used by some species of fish which live in brackish water, where there is not always a good amount of oxygen dissolved in the water itself. Such fish would have a head-start to take advantage of opportunities on the land near the water's edge.
Seems to me there would be a lot better (and easier ways) of becoming more dominant in the environment they already knew.
"Easy" is not a consideration for evolution. It doesn't "look ahead" and "decide" what would be the path of least resistance.
And you should ponder how "easy" it is to remain in the water somewhere down near the bottom of a predatory food chain, versus moving into a niche where there would be (at least at the start) no predation and no food competition.
Also, if they lived in the sea and could not walk and stuff, how did they know there was an 'empty niche' on land? Who told them? Does natural selection have esp??????????????
If that's a serious question, you need to try harder. If that's a faceitious question, you need to try to think up some serious ones.
The early amphibians most likely started just skipping from pond to pond to look for greener pastures when their current pond couldn't properly support them. From there, they were in a good position to begin to spend more time on land (to avoid predation in the water) and to begin to take advantage of whatever food was appropriate for them (i.e. insects, vegetation, etc.) as they made their overland travels. Over time they'd become better adapated to longer stretches on land, taking more and more advantage of the resources there.
It's similar to, but the reverse of, how some families of mammals (which were at one time 100% land-based) began migrating towards spending more time in the water. Whales ended up living full-time in the water, whereas walruses, sea lions, and hippos are clearly very adapted for water life, but still reside some of the time on land.