There was a market for whether "love is the most important thing in the universe". Let me make an improved version with a more plausible claim. I want to see how it fares comparatively.

Within "reproduction", I include many things related to reproduction by natural selection, such as sexual and asexual reproduction, sex, hormones, carnal pleasure, romance, love, and other things that might be directly related to reproduction by natural selection.

Interpret "important" however you prefer. The ambiguity makes it kinda interesting.

I exclude the necessary physics for biological entities to exist in the first place as an alternative answer to the question. I simply take them as a given. By this, I mean that the existence of dimensions, space, time, atoms, gravity, the nuclear forces, electromagnetism, planets, heat, and other preconditions for life are presupposed and thus disqualified from the competition as "more important".

Conditions for resolution: I will let the market stabilize for three months, and then if it reaches >80% I will resolve YES, and if it reaches <20% I will resolve NO. Otherwise it will stay open indefinitely. I could resolve N/A if I see blatant market manipulation (including cases such as the market being decided by a single person betting a ton on money on one side).