Eli5: How was the first ancient animal to ever step (foot?) out of the water, able to survive breathing air instead of water?

Question

Eli5: How was the first ancient animal to ever step (foot?) out of the water, able to survive breathing air instead of water?

In: Biology

Answer 1

It wouldn’t have been a switch, or a moment. Like, one day it’s a fish the next day it’s a lizard, it would have been a transition.

For example, if you look up videos of an octopus walking across land, it becomes easy to imagine how generations of octopi with stiffer and stiffer cartilage would be more & more efficient, and that’s how bones evolve. Similarly, when a creature peaks its head out of water and a mutation makes it 1% better at using atmospheric oxygen, maybe that’s not enough to leave the water, but one of their offspring mutates to be 1% better, and one of their offspring is 1% better, and one of their offspring is 1% better, and, and, and…. enough mutations happen over enough generations, and you have a set of lungs.