Depends on your beliefs, really. I do not think their is a correct answer here. Some may say to continue on the human race and another may question that statement with "why should the human race continue on?" Is there a bigger picture here?
Why are we able to ask ourselves these questions when a dog or cat is not yet we still have the same reproductive functionality of both.
I would say ask yourself what you think your purpose is here, maybe it is something like taking care of your child, being a florist or space travel. Whatever you believe your purpose to be is probably why you were born.
Unless of course one day the sky opens up and some guy looks down at his project and tells us we are all part of his sons middle school biome science project.