Why is reproduction necessary?

For survival of the species,
Zero reproduction means extinction.

Perhaps your real question is why should we care whether we go extinct or not. In that case, the answer is that we care because we consider life precious and worthy of being preserved.

Reproduction is necessary to provide offspring however I think you may mean why do we need sexual reproduction and in animals this is due to our very rigid plans for body and cell structure. In plants this is not the case and my second year of botany has drilled into us that there are some species which survive entirely on asexual reproduction or apomixis (seeds produced asexually as in some weeds). This plant only occurs in a remote section of tasmania, Australia (where I live). The MAJORITY of plants use sexually as it enables a greater variation in genetic makeup of a species thus provding greater evolutionary fitness. This is not to say asexual is bad but just not as effective long term as sexual.

If this is what you wanted I hope I helped but if not I apologise for my prattle.

By

Sekhmet