Did you find an answer to your question, op?

Let's have another round, Nobody2, nice bump!

A single living organism evolves.

A volcano erupts on-top of the single living organism. All life dies.

Another single living organism evolves.

A rock falls on-top of it blocking all sunlight. All life dies.

Third time lucky: another single living organism evolves. It (somehow) duplicates/reproduces. Its offspring gets carried away by ocean currents to a different part of the world. A volcano erupts killing one of them, but the other stays alive, to duplicate/reproduce again. Life survives.

So the answer to why?

Risk diversification.

Another answer to the why (with regard to transition from duplicating to reproducing) is:
To make DNA more resilient against viruses.

P.S. the word 'why' is better replaced with 'how', unless you prefer to implicitly bring God/s into your reasoning.

TL;DR: replication could have occurred due to a selective pressure of an over abundance of raw materials for maintence of life and the inability of rudimentary systems to control for that abundance. Reproduction could be the most efficient way evolution could duplicate single cell replication in multicellular organisms given the existing systems at the time of multicellular development.

Explanation

If I had to give an opinion as to why replication (i.e. the first form of reproduction) took place I would say it was response to an environment with abundant raw materials for replication and deficient in stimuli that would cause the lifeform to use as many resources as it was taking in for general survival. I will elaborate here.

The life form's basic task would have been to maintain itself. For something like a cell that would mean, on the most basic level, keeping the outside from coming in and the inside from leaking out. This would require some mechanism to maintain the barrier between inside and out. This means bringing in raw materials to maintain the barrier and expelling unwanted materials whatever their origin may be.

So the question becomes how does the lifeform deal with an influx of additional raw materials via this pathway of material gathering and barrier support when there is no demand for their use?

Some of the most general options I could imagine (not exhaustive):

1. Do nothing and intake resources as normal.

1A. Store the excess raw materials, intermediaries, or final products for later use.

1B. Consume the resources and increase in size.

1C. Consume the resources to replicate

1D. Develop a mechanism to remove and replace perfectly normal internal systems.

2. Evolve an expulsion mechanism for excess raw materials.

3. Evolve a mechanism to regulate the uptake of excessive raw materials.

Without going into too much detail on the other options, 1C seems to me to be the most cost effective solution from a time and energy investment to the problem. The lifeform already has a mechanism in place to consume raw materials and replicate pieces of itsel so that making more life forms seems like an easy next step.

Reproduction on a multicellular scale is similarly likely the most energy and time efficient way that has evolved to replicate multicellular organisms.

There are plenty of things in the world that don't reproduce - we just don't consider them to be living. If the question is, instead, why does anything reproduce at all, it's probably just statistical - the universe is very large and reproduction only had to emerge once for the universe to have lots of self-reproducing entities.

It's fun, that's why.

Why do living things reproduce?

If they didn't, they wouldn't exist.

lol thats a terrible answer to the op.

a poaster above had a good response with the whole raw materials stuff. ive wondered this question myself. i think RNA was important for the origins of life because its a complex compound that can repair dna. the fact compounds exist that can modify dna, the possibilities become staggering including asexual reproduction. the origins of reproduction were asexual, dna-chromosomes splitting in two. at some point (i have researched this at all) asexual organisms bumb into other asexuals or something something, leading to sexual reproduction.

It's pretty accurate though. Reproduction is not limited to sexual reproduction.

Thanks, chez.

This is not an advocation for my previous answer but the answers 'because they wouldn't be here' or 'because the universe is this way' or 'it was bound to happen given the infinite nature of the universe' are ,imho, cop outs for questions that MAY be answerable through science.

For example 'Because the universe operates that way' is a perfectly reasonable answer to 'why does water freeze' but we know there are better answers to that question.

If you don't think there is utility in an answer and thus the investment to discover the answer is too significant for the utility, that seems reasonable.

Except it's not a cop out like 'the universe is that way'.

'Because they wouldn't be here otherwise' is explanatory. Life could in principle exist without reproduction but in reality life is pretty much just a result of the reproduction process.

Science (barely even science is needed) has answered it - there's just some trivial details to fill in.

Because they can.


PairTheBoard

This remains the best answer.

It needs us to simultaneously think individual and species though. The individual of course exists also without reproducing. Compare it to a chain. The last link is only tied to the previous one, there is no next link. But they are all part of the chain, and it has emerged through reproduction.

But theoretically, a for ever living being, emerging from unorganic stuff, could afford not to reproduce, and could exist without it. But I think death is almost unavoidable for both survival and development, and then you get reproduction as basis for existence.

plaaynde brings up the point I was going to restate from others in tge thread.

The answer 'because they wouldn't be here' isn't as large of a cop out as 'that's the way the universe is' but it still doesn't answer questions directly related to the OP 'why was reproduction selected for over other options' or 'how did reproduction arise' and that answer doesn't really satisfy those questions.

Edit: We may never know the answer to those questions or to even formulate ways to try and answer them and that's fine but that doesn't make my point any less relevant.

For something to be called life, there has to be some kind of growth. You are starting out with molecules, they have to grow bigger. Because it's so unlikely something grows by itself from scratch, there has to be some copying/template mechanism.

Now we have established there has to be growth. When it grows big enough, it will be too big for sustaining itself, because the area of the border to the outside world becomes too small as compared to the volume. Then it will have to split in some way, that is, reproduces.

And one single organism may be destroyed at any moment. If it splits, that is reproduces, it can spread out, and lessen probability of destruction.

Nice combination: putting an end to overly growing and spreading risk at the same time. Try to beat that!

I don't think life has to be determined by growth or that reproduction is the only solution to controlling growth. It's been awhile but I'm not even sure that size is even a determining factor for cellular reoroduction (i.e. I reach size X and I split), but I can agree it's probably a limiting one (i.e. I must be size X before I can split).

I am familiar with the surface area to volume ratio problem in terms of cell size but really that's just a limiting factor for how large a cell can be and reproduction is only one solution to that problem.

I certainly agree that reproduction is a great solution to the growth problem and it may very well be the right answer, but I don't think the premise of all life grows necessary.

Spreading risk is certainly a valid answer given multiple times in the thread. Selected for because more life there is has a better chance of surviving events that terminate life.

Whichever process there is that causes growth in the starting life, it will be self-poisoning at some point. If the templates just continue growing (copying or something similar) and just stick together, the very process will stall when substrate can't diffuse into the growth process because it has become too big. Separation (=reproduction) makes it possible for the growth process to continue. And then it happens to be a huge benefit because of the risk diversification.

The point with this is that also the individual benefits from reproduction, not only the species.

The Hive.


PairTheBoard

A bit of expansion:

From the viewpoint of the individual, growing too big for substrate diffusion to happen smoothly, it benefits from getting rid of some "garbage", that is, parts of itself. Paradoxally some of those "pieces of garbage" can, as they are separated, start the process over. So we have a win win situation.

So reproduction is both the original individual getting rid of a burden, and a new individual getting/claiming its freedom.