Are there evolutionary reasons for reproduction?

Hi MrQ, welcome to EvC!There's a simple way to put quotes in neat little boxes as to make your posts easier to read:

I kind of sum of the whole argument in following diagram. each -> means (existence depends on):reproduction -> having variations -> better adaptation -> live longerI would appreciate if somebody endorses this or comment on it as I want to take it further.

Reproduction causes variation which may lead to enhanced adaptation which may allow an individual to survive long enough to procreate.

Thanks, then relation between reproduction and variation is different than others. So lets take ~> as "may cause" and change the name of -> to "definitely cause"reproduction -> variations ~> better adaptation ~> live longer ~> better reproductionIt seems to me reproduction's job is to create variations and variation's is to create more reproduction. However all this is limited by the energy consumption. More reproductions, means more energy consumption therefore, some organism develop the habit of living longer instead of reproducing more to extend their species life span. So I am not so sure about the last bit of the diagram. Do species live longer to better reproduce or save energy?

This type of question indicates that you are still completely misunderstanding the issue.Evolution basically points out that the offspring of one generation is based on the previous generation, thus those that survive and reproduce more successfully tend to become dominant in the population. There is no "intent" behind the process required or indicated.Species don't live longer to better reproduce, or to save energy. They live longer *because* it tends to increase their numbers; or more accurately there are more of those around that are better suited to be around than those that are not. The explanation for this phenomenon might include the conservation of development energy but the mechanism itself "just works".Reproduction and variation don't have "jobs", they have results. It makes no sense to say that a rock falls off a cliff because "it's job is to reach the bottom of the cliff", and it makes no sense to talk about reproduction as having the job of creating variation.

The environment determines if a species will evolve towards higher fecundity (many offspring) or towards longer life expectancy.You should read up on r/K selection theory

quote:

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r-selection (unstable environments)
In unstable or unpredictable environments, r-selection predominates as the ability to reproduce quickly is crucial. There is little advantage in adaptations that permit successful competition with other organisms, because the environment is likely to change again. Traits that are thought to be characteristic of r-selection include: high fecundity, small body size, early maturity onset, short generation time, and the ability to disperse offspring widely.

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Organisms whose life history is subject to r-selection are often referred to as r-strategists or r-selected. Organisms with r-selected traits range from bacteria and diatoms, through insects and weeds, to various semelparous cephalopods and mammals, especially small rodents.

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K-selection (stable environments)
In stable or predictable environments, K-selection predominates as the ability to compete successfully for limited resources is crucial and populations of K-selected organisms typically are very constant and close to the maximum that the environment can bear (unlike r-selected populations, where population sizes can change much more rapidly).

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Traits that are thought to be characteristic of K-selection include: large body size, long life expectancy, and the production of fewer offspring that require extensive parental care until they mature. Organisms whose life history is subject to K-selection are often referred to as K-strategists or K-selected. Organisms with K-selected traits include large organisms such as elephants, trees, humans and whales, but also smaller, long-lived organisms such as Arctic Terns.

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I found a pic too:

Natural selection does not occur at the molecular level. It happens at the organismal and population level. It is the organism as a whole that reproduces, not a molecule within the organism.Also, how many organisms alive today are the descendants of ancestors who did not reproduce?

I imagine the result would be the same and that's survival. You're trying to attach too much reason to it when it simply comes down to survival.An organism that lives a long time may produce less offspring but has a chance to reproduce again and if one of those offspring's offspring reproduce we have a success story. Species like this normally would have better "reason" to adapt better to the environment. In this case mutations that extend the life of the organism might be selected.On the other hand mayflies only live for a day almost all energy goes into reproducing. This species would produce MANY offspring. mutations that produce more offspring would be selected over ones that don't.Both systems work. When looking at life and survival it might be better to think of it more like "Whatever works." I don't think there has to be a reason beyond thatEdited by DC85, : No reason given.

Hi allThanks for all contributions. It is really interesting debate. This type of comments came up several times. I guess my postings had the same fate as "selffish gene" misunderstandings. I totally understand that species or evolution itself doesn't have conciseness and the process goes forward randomly. But as time moves forward, there is a virtual sense of reason and direction enforced by the overall process. Therefore, there is a overall reason behind every step of the evolution and that is what I am interested in. I presented part of it in the diagram and interested in make it more complete. We assume that the randomness of the event can cause some steps against the direction but as time increases the overall direction should stay the same.Catholic Scientist has made good contributions as well. Considering your and his/her remarks I deduct following statement.In evolution "longer existence" is species is important. Organisms takes different strategies to achieve it. Some develop short life span and higher reproduction rate and some longer life span, more intelligence and lower reproduction which also saves energy. Therefore I change my diagram to following:reproduction -> variations ~> better adaptation ~> longer existence(survival)Therefore both reproduction and variations are working together to achieve only and one only final goal of longer existence of each species. Is this better?Edited by MrQ, : survival

No. "Longer existence" is not a factor. "Just long enough to reproduce" is the factor.If the variations that are produced by imperfect reproduction are beneficial then survival may be enhanced to achieve further reproduction. But this not a "goal." If the variations achieve a shorter life span with more prodigious reproduction then this strategy may survive as well.All that is happening is imperfect reproduction of individuals that are fit just enough to survive their environment to reproduce the next imperfect generation. The resultant variations of populations over time is called evolution.Edited by AZPaul3, : No reason given.Edited by AZPaul3, : more corrections

I think the thing to remember is that chemical reactions occur.There for, replicating molecules (which are chemical reactions) replicate because of the physical properties our universe has.Just like 0 degrees C is the triple point of water: that is the way H20 behaves.There is no 'advantage' to the environment when water melts or freezes or evaporates. The only thing that happens is the 'normal' behaviour of atoms and molecules.Replicators replicate because of the physical properties they have: extraneous entities need not apply.ABE: As Wounded points out: it's not a closed system.Edited by Larni, : Last sentence

You're getting closer... All that matters is that the organism lives to reproduce.That isn't the purpose and there is no purpose for it other then the fact that it worked. Confused?Stop thinking about purpose and try to look at it like "it's good enough".
It makes more sense that way I promise

I have read this in other biology text. But according to what we discussed, it is not true. The correct sentence would be "Survival should be at minimum long enough to reproduce". Therefore, survivals or longer existence can far surpass the reproduction age but as far as the species in the overall can maintain their existence then it should be fine. This is also true from following facts:Assumption: Evolution process can't foretell the future therefore evolution is not bounded by any time limitLim t-->inf (t is time)
number variations that is needed to reach certain adaptation = N
number of variations/t= Variation rate(v)Then we consider two species x and y, x has got high birth and death rate but enough to survive as v is high in x then probability of reaching to N in time T1 is P.For Y if the probability of reaching N is also P but because variation rate is significantly lower than x then it reach to that level in T2.It is apparent that T1>T2, means that X reaches adaptation faster. But as evolution is not bounded by any time limit, there will be a definite time that Y also reaches the adaptation necessary only and only if it can survive for T2. Therefore, survival to adapt(in digaram these two is shown to be related) is the key factor here not survival to reproduce. Reproduction is just the basic requirement and is not critical factor in the rest of the process as I see it here. But as you can see in the diagram it certainly relates to other factors. Therefore, if reproduction drops to certain level that the survival gets in trouble then that species will be doomed.reproduction -> variations ~> better adaptation ~> longer existence(survival)If anybody have comments on this please mention as I want to take it further.

What I meant by sentence "reproduction is there to create variation" was in long term evolutionary process. Chain reactions happen but they soon use all the resources and the process ends there. The chemical reactions becomes like simple burning a wood, it happens as far as it has the fuel and air and finishes to a dead end. Some reactions are energy dependent. For example like turning water to ice and vise versa. These reaction happen periodically as the source of energy comes and goes. Like for example in day ice gets warm and turns to water and at night freezes. So this process goes on forever but nothing can come out of it in terms of adaptation or evolution. To have evolution you MUST have reproduction and you MUST have variations at the same time unless it doesn't work.

Correct. Evolution is the mathematical result of reproduction and genetic variation. Populations evolve because individuals reproduce differentially. This why your OP question does not make much sense. There is no evolutionary reason organisms reproduce; reproduction is an initial requirement, not a product.

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We have many intuitions in our life and the point is that many of these intuitions are wrong. The question is, are we going to test those intuitions?
-Dan Ariely