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What is the biological factor (gene or something else in case of humans) which motivates an organism to reproduce?

By reproducing the evolutionary success of an organism increases. But why would an individual organism care about evolutionary success? Is there something inherent in the body of an organism that motivates the organism to take part in reproduction? From an organisms point of view, it can very well live happily without reproducing, in fact, the act of reproduction might lead to eventually more difficulties (raising the offspring, protecting the offspring etc.).

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    $\begingroup$ "But why would an individual organism care about evolutionary success?" - Every organism that didn't died without reproducing; you only see the ones that reproduced. $\endgroup$
    – Bryan Krause
    Nov 22, 2022 at 19:25
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    $\begingroup$ "you only see the ones that reproduce" - so the evolutionary success is the driving force of reproduction? I don't think a simple life form (let's say a bacteria) can understand evolutionary success, but still it none the less optimises for evolutionary success? What forces it to optimize for it? $\endgroup$ Nov 22, 2022 at 19:33
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    $\begingroup$ Nothing forces anything; organisms with a genetic tendency to reproduce will reproduce and you'll see their offspring in a future generation. Any organism with genes that prevent it from reproducing will not reproduce, and you won't see their offspring in a future generation. $\endgroup$
    – Bryan Krause
    Nov 22, 2022 at 19:41
  • $\begingroup$ As a new user of this site we expect you to do us the courtesy of finishing reading the Tour to find out how this site works and read the Help on asking questions. We expect posters to demonstrate that they have done some research themselves. This topic must be covered amply on the Internet. If you find the answers there unsatisfactory, please tell us why. $\endgroup$
    – David
    Nov 23, 2022 at 10:24

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You are confusing proximate and ultimate causes.

What causes an organism to keep eating, most are not smart enough to know they will die if they don't eat. The ultimate reason may be to keep from starving but that is not the proximate reason.

The proximate reason they eat is because their brains are built to want to eat when their senses detect food. to get hungry and feel pleasure when that hunger is sated.

eating, drinking, scratching, pain, disgust avoidance, vomiting, reproduction, they all come with basic urges, proximate motivations. the brain is built to want to do these things under the proper conditions. Why do songbirds sing, because they want to, they have a desire to and acting on that desire in the correct circumstances gives them pleasure or not acting on it causes discomfort.

Animals have sex because they want to, that is the proximate cause. The ultimate reason they want to is brains with that desire are the brains most likely to pass on their genes to the next generation. Thus genes that make brains that get the animal to reproduce are the genes most likely to make it into the next generation.

To look it another way you are the product of an unbroken line of genes that built brains that reproduced, because genomes that did not don't leave descendants.

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    $\begingroup$ +1 for introducing a new idea. $\endgroup$ Nov 25, 2022 at 4:05
  • $\begingroup$ I reached to this independently and I had no idea before just randomly. $\endgroup$ Jul 10, 2023 at 21:30
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Life processes are ways of long term survival of genetic information, being carried by individuals with momentary lives inside their cells.

Since each individual life is momentary, only that genetic information survives for a long time which has developed efficient ways to ensure individuals continue to bud off new ones before they die.

In other words, individuals are only tools in the control of the super-organism of genetic information. And thus, it is not surprising to find only those variations of genetic information continuing to survive around us which have been able to drive their individual buds to continue to replicate. This includes driving the individual to resist death, driving it to seek and gather resources, and driving it to reproduce.

The tree of genetic information continues to find these ways of driving individual buds primarily through chance, enabled by the huge number of tiny variations that it introduces in each individual, and the humongous numbers of individuals; when a branch (or twig) of the genetic tree can no longer ensure it, it dies out.

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    $\begingroup$ I always thought sexual urges had something to do with it. $\endgroup$
    – David
    Nov 23, 2022 at 17:11
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    $\begingroup$ "Individuals are only tools in the control of the super-organism of genetic information." I'll use that line next time someone takes themself too serious if you don't mind.. ;) $\endgroup$
    – iLuvLogix
    Nov 23, 2022 at 17:29
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    $\begingroup$ -1. Humans aren't forced to reproduce. More and more humans don't reproduce now that 1. children are no longer necessary for labor/elder care and 2. contraception is widely available. Many humans who accidentally may or do conceive prevent or end their pregnancies. If we were forced genetically to reproduce, these choices would not exist. $\endgroup$ Nov 23, 2022 at 20:54
  • $\begingroup$ @anongoodnurse I agree that "driving" could be a better verb than "forcing" here. Thank you so much for pointing it out. I have replaced it. I am sure you know that my usage of "force" wasn't meant to be irresistible; quite difficult to resist but not irresistible. $\endgroup$ Nov 24, 2022 at 2:57
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    $\begingroup$ @iLuvLogix Thank you so much for valuing it, and thank you even more for telling me that you value it. I also find the idea philosophically humbling. I have now emboldened it for cursory readers. $\endgroup$ Nov 24, 2022 at 3:01

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