I know I never post here but I have input for the debate. It depends what you mean by the meaning of life, really =\ This explanation is assuming the topic is pondering why humans live.
Human beings are, as science tells us, animals - primates to be exact. In a similar fashion to animals, all of the way through our life, we do things to help us survive - we eat and drink, we breathe and so on and so forth. A lot of the time, we don't even know that we're trying to survive for, but it's an instinct. Surely the thing we do most is the reason we live?
That's the main purpose of life sorted, but then what do you humans survive for? All animals do certain (As our science teacher was telling us), and he used the boys on the field at break time as an example of this. They try to attract a mate, as do animals in the wild. They are constantly fighting and showing off (Similar to monkeys fighting), to attract the girls. They might think that they're having fun, but they're trying to show the girls that their genes will give their offspring strength and power. The girls (As animals), want their offspring to survive and being strong will allow them to fight off predators and being strong allows you to survive(
We must remember that humans would be preyed on in the wild before guns existed, as we would be vulnerable to lions etc. It is only with our developed brain and ability to perform certain actions that we have escaped this vulnerability to be the most powerful species on the planet). The girls on the field would be more attracted to the boys which win the fights, because their genes would produce strong offspring which are more likely to survive, so this "playful fighting" has potentially won them a mate.
This leads me to the conclusion that humans exist to survive, and pass on our genes through reproduction (Sex, to make all the twelve year olds giggle).
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