Things are done and dusted only in religion. Not in science. Things change, even genious discoveries are build upon or disproven many years later. Just a couple of months ago CERN announced they might have discovered a particle that moves at a speed greater than the speed of light. If they can prove this it would ruin a lot of Einstein's theories, or at the least build upon them. There's nothing set in stone in science - it evolves.
As for pain during child birth. Evolution and pain have nothing in common whatsoever. Evolution does not care about pain, it doesn't give a shit about it as long as the species survive.
For what it's worth a lot of the animals are much better off than humans when it comes to birth, both as an easier way to do it and as their offspring being more or less self-sufficient in hours, days or weeks, unlike human babies, who need to be taken full care of for years. It only proves that human is not the be all and end all of evolution. No problem with that. There are countless of examples that show that different types fo animals have evolved certain aspects much better than human - eyesight, being able to survive for months without eating, etc.
No one says that man should be the best evolved in all possible aspects compared to animals, neither does it mean that there is a certain time period over which a man should or should not evolve in a certian manner, i.e. it might take 10 million years for man to stop feeling pain when giving birth, or a few thousand years or it might never happen. Means nothing from an evolutionary point of view - if the pain is too bad and prevents people from mating and giving birth, then the species will disappear from the face of the earth. Evolution doesn't give a **** about it.