How or why did reproduction evolve?

[Mick116]

It seems that organisms have evolved an inherent desire or instinct to reproduce and thereby pass on their genes - but how or why did reproduction first evolve? Why do genes seem to be competing for a place in the gene pool, so to speak? Has anybody read some theories?

If there are inherent misconceptions in the wording of my question, please point them out.

 

[gluadys]

It seems that organisms have evolved an inherent desire or instinct to reproduce and thereby pass on their genes - but how or why did reproduction first evolve? Why do genes seem to be competing for a place in the gene pool, so to speak? Has anybody read some theories?

If there are inherent misconceptions in the wording of my question, please point them out.

It's a little off the mark to speak of an instinct or desire to reproduce evolving as there has never been a life form that did not reproduce. Reproduction is considered to be one of the identifying characteristics of life. (Not that every individual organism needs to reproduce, but reproduction must be characteristic of the population.)

As far as I understand it, replication of RNA and DNA began even before there was life. This is simply part of the chemical property of these molecules. The origin of these self-replicating molecules is itself being researched.

At the level of cellular life, I understand that reproduction occurs as a result of the growth of the cell. It has to do with volume increasing faster than surface area and the cell needing to split into two to maintain the necessary capacity to exchange material between the inner region of the cell and its outer environment.

As cells began to form colonies and complex organisms, certain cells took on particular tasks and one was reproduction.

 

[crawfish]

Because God loves us.

 

[Mick116]

It's a little off the mark to speak of an instinct or desire to reproduce evolving as there has never been a life form that did not reproduce. Reproduction is considered to be one of the identifying characteristics of life. (Not that every individual organism needs to reproduce, but reproduction must be characteristic of the population.)

As far as I understand it, replication of RNA and DNA began even before there was life. This is simply part of the chemical property of these molecules. The origin of these self-replicating molecules is itself being researched.

At the level of cellular life, I understand that reproduction occurs as a result of the growth of the cell. It has to do with volume increasing faster than surface area and the cell needing to split into two to maintain the necessary capacity to exchange material between the inner region of the cell and its outer environment.

As cells began to form colonies and complex organisms, certain cells took on particular tasks and one was reproduction.

Thanks gluadys!

I guess a more appropriate phrasing would be, how did reproduction "originate" rather than "evolve", since reproduction is a prerequisite for biological evolution.

At the chemical or even the cellular level, I would also suppose that "desire" or "instinct" were inappropriate to describe a tendency towards reproduction.

 

[LewisWildermuth]

Thanks gluadys!

I guess a more appropriate phrasing would be, how did reproduction "originate" rather than "evolve", since reproduction is a prerequisite for biological evolution.

At the chemical or even the cellular level, I would also suppose that "desire" or "instinct" were inappropriate to describe a tendency towards reproduction.

Chemistry, unfortunately I am not a Chem major...

Basically through chemical reactions simple compounds can become more complex, sometimes these more complex can reproduce themselves.

Unfortunately for our studies, these processes are usually stopped by free oxygen, something we have a lot of not but the early Earth had little of until life was well established.

Even with these difficulties there has been a lot of interesting research in this area in the last twenty years.

Hopefully someone will be able to find good links for you on this.

 

[shernren]

Do you mean reproduction in general, or sexual reproduction in particular? Most of the time when this is raised as a difficulty for evolution (not that it's not a valid question) it's normally referring to sexual reproduction.

The origin of both are quite different.

 

[Mick116]

Do you mean reproduction in general, or sexual reproduction in particular? Most of the time when this is raised as a difficulty for evolution (not that it's not a valid question) it's normally referring to sexual reproduction.

The origin of both are quite different.

I'm interested in how reproduction in general originated.

 

[shernren]

Cool. Well, you'd have to define reproduction. The basic question is: how do molecules make more of themselves? And the answer is: via autocatalysis.

(The following is basic chemistry on rates of reaction, so forgive me if I sound patronizing. I don't intend to.)

Chemicals react at a given rate that varies with certain reaction conditions. Anybody who's mixed vinegar with soda knows that fizzing happens immediately (or to kill it with chemical-speak, large amounts of carbon dioxide are quickly evolved), while on the other hand iron takes days to rust even when it is left out in the open with plenty of water. There are fast reactions and there are slow ones. So how do you speed a reaction up? Essentially, reactions happen more often when the reactant bits (atoms, molecules, or ions) slam each other in the right configuration. So you might simply try to make those bits slam each other more often, which you can do by simply increasing pressure, or temperature, or the concentration of the reactants.

But there's another way: it involves adding a catalyst to the mix. A catalyst doesn't make your reactants collide more often. What happens is when your reactant bits slam into the catalyst, the catalyst essentially rearranges them so that they are in the right configuration, and so while the amount of collisions doesn't change, the proportion of successful collisions does.

So what would happen if you could find a catalyst that could put itself together? That would be autocatalysis. And we have indeed seen autocatalytic molecules in nature. For example, amino adenosine triacid ester (AATE) molecules, when put in a solution containing raw materials that can be used to construct itself, readily puts them together like any dutiful catalyst would - except what it's making is more of itself, which then catalyses the production of even more AATE, which then ... you get the idea?

AATE is more of a proof of concept; since it's not being used today in any known lifeform, it's highly unlikely that this was actually how life started reproducing. However, RNA also has autocatalytic properties. RNA is known to form "ribozymes", or ribonucleic-acid-enzymes, and some ribozymes also have the capacity to put themselves together. So at least one origin-of-life hypothesis says that the world started out with just RNA - an "RNA world" - and then life developed when the autocatalytic loop widened. Instead of simply chemical A catalyzing its own formation, you get additional steps being put in - chemical A starts to catalyze the formation of chemical B, which catalyzes the formation of chemical C, which catalyzes the formation of chemical D, which then loops right back round and catalyzes the formation of chemical A.

I hope that satisfies your curiosity.

 

[Mick116]

Cool. Well, you'd have to define reproduction. The basic question is: how do molecules make more of themselves? And the answer is: via autocatalysis.

(The following is basic chemistry on rates of reaction, so forgive me if I sound patronizing. I don't intend to.)

Chemicals react at a given rate that varies with certain reaction conditions. Anybody who's mixed vinegar with soda knows that fizzing happens immediately (or to kill it with chemical-speak, large amounts of carbon dioxide are quickly evolved), while on the other hand iron takes days to rust even when it is left out in the open with plenty of water. There are fast reactions and there are slow ones. So how do you speed a reaction up? Essentially, reactions happen more often when the reactant bits (atoms, molecules, or ions) slam each other in the right configuration. So you might simply try to make those bits slam each other more often, which you can do by simply increasing pressure, or temperature, or the concentration of the reactants.

But there's another way: it involves adding a catalyst to the mix. A catalyst doesn't make your reactants collide more often. What happens is when your reactant bits slam into the catalyst, the catalyst essentially rearranges them so that they are in the right configuration, and so while the amount of collisions doesn't change, the proportion of successful collisions does.

So what would happen if you could find a catalyst that could put itself together? That would be autocatalysis. And we have indeed seen autocatalytic molecules in nature. For example, amino adenosine triacid ester (AATE) molecules, when put in a solution containing raw materials that can be used to construct itself, readily puts them together like any dutiful catalyst would - except what it's making is more of itself, which then catalyses the production of even more AATE, which then ... you get the idea?

AATE is more of a proof of concept; since it's not being used today in any known lifeform, it's highly unlikely that this was actually how life started reproducing. However, RNA also has autocatalytic properties. RNA is known to form "ribozymes", or ribonucleic-acid-enzymes, and some ribozymes also have the capacity to put themselves together. So at least one origin-of-life hypothesis says that the world started out with just RNA - an "RNA world" - and then life developed when the autocatalytic loop widened. Instead of simply chemical A catalyzing its own formation, you get additional steps being put in - chemical A starts to catalyze the formation of chemical B, which catalyzes the formation of chemical C, which catalyzes the formation of chemical D, which then loops right back round and catalyzes the formation of chemical A.

I hope that satisfies your curiosity.

Thanks shernren!

 

[shernren]

No problem. Another thing to remember well is that the first "life" must have looked extremely different from life today. We think of life as puppies and trees and us; life when it started was really a bunch of interacting chemical reactions that happened to make more of whatever you put in at the start.

 

[Mick116]

I'd be keen to better understand natural selection amongst those early reproductive chemicals - obviously certain chemicals would have had "traits" that allowed them to survive and reproduce more effeciently in their environment than others. I assume the addition of an oily membrane must have been beneficial to survival.

I wish I still had some relevant textbooks or access to some scientifc journals, but alas finances are a little tight at the moment, and my current knowledge of chemistry is severely wanting. And Google hasn't been much help.

 

[shernren]

Well, here's a little exercise for you. Imagine you have a bunch of chemicals floating in a suitable mix. Some of them can manufacture copies of themselves.

Of the chemicals that can clone themselves, how would you judge which are the best? What criteria would you use?