What's the purpose of genders in evolution

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I'm working on an experiment where I mimic biological evolution. I'm doing sexual reproduction to allow gene swapping because I see it as beneficial in terms of evolution.

I got to wondering if I should include genders in my simulation. What is the evolutionary reason for only allowing half of the population to mate with the other half of the population? Stability seems like a probably one, but is there something else? What affects would it have on evolution if every member of a species was capable of mating with every other member? (Except for relatives which my algorithm forbids because of replactive fading.)
 

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  • #2
Simon Bridge
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What is the evolutionary pressure for half of the population [being restricted] to mate with the other half of the population? ... What affects would it have on evolution if every member of a species was capable of mating with every other member?
If every member of a population can exchange genetic material with every other member - what prevents self-fertilisation?
In macroscopic organisms there may be an advantage to specialising sex roles as there is to any specialisation - division of labour in social species perhaps? (ie it guarantees that no more than half the population is impaired or otherwise inconvenienced by pregnancy).
Dividing the population like that produces a competition for mates - could there be an advantage to that?
That should start you thinking in a profitable direction - there are also many articles online covering evolution of gender.

Note: there are hermaphroditic species - they tend to be unusual among sexual animalia. One way to see the effect is to compare similar specialised and hermaphrodite species. There is also a large body of literature on the subject.
 
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So everything you listed has to do with complex behavior of the species. That'd be irrelevant to a creature like a worm.

I suppose segregating the genes into two groups would be required to avoid self fertilization in real animals.

Simulated ones don't have the problem of self fertilization or the complex behavior of post Cambrian animals. I should have mentioned that the simulated creatures have the intellect of tadpoles.

I will continue to research along these lines.

Seems that if you have multiple parts that have to fit together, mathematically two are the most likely to be at the same place at the same time, but it's still just about a mechanism for gene swapping, so I see no reason my simulation should include genders.
 
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Simon Bridge
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So everything you listed has to do with complex behavior of the species.
That'd be irrelevant to a creature like a worm.
So it is not important that worms do not self-fertilise? (1st item on my list.)
You will have noticed that sexual dimorphism is dominant in species which have quite complicated behaviour, just as asexual reproduction dominates in organisms that are very simple. Could this be a clue?
... My list was incomplete of course - there are thousands of possibilities and I have no clue which would be relevant to you.
I should have mentioned that the simulated creatures have the intellect of tadpoles.
... tadpoles are pretty complicated multi-cellular organisms with complex behaviours - they are a funny example. You realise that frogs are sexual creatures right? Are you sure about this characterization of the simulated organism?
Simulated ones don't have the problem of self fertilization or the complex behavior of post Cambrian animals.
That is correct - you can make your simulation to avoid all kinds of issues that would arise in Nature simply by not encoding them, or ensuring behaviour by Programmer Decree. For instance, you can ensure perfect gene replication through many more generations than Nature can, and you don't have viruses, viroid, and prions inserting rogue genes into the mix just by not programming them in to your simulation. You get to do that when you are making stuff up as you go.

The thing is, you did not ask what the advantages would be for the simulation, you asked what the evolutionary advantages were... period. You did this in a biology forum. If you want to know about the advantages are from a programming perspective, then try the computer forums... though you'll probably have to divulge more about the purpose of your program.
 
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I chose to put it in the biology forum because I wanted to know what purpose it served on earth as a whole. I'll then determine whether or not it's worth looking into the benefits on a computer. I'm making a list of pros and cons and want to make sure that I don't miss any pros. I plan on asking advise in the programming forum in a few days on my experiment.
 
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Ygggdrasil
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The discussion so far has been quite animal-centric. Plants reproduce sexually, but they have no genders as each individual generally produces both male and female gametes.
 
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BillTre
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I strongly second @Simon Bridge's argument about not self-fertilizing.

Although some species have dropped sex and reproduce parthanogenetically, self-fertilize, or clone themselves, they are thought to be limited in an evolutionary sense because their genetic diversity (as a population) is much more limited than sexually reproducing organisms.
Problems include: adapting to changing environments, evolve away from parasites, can't evolve new species because change is limited, can't easily get rid of bad mutations that they might acquire.

Even single celled yeast have mating types that require two different mating types to mate.

Some Exceptions:
Some worms can have a reproduce by self-fertilizing (Caenorhobditis elegans hermaphordite sex), but the species also has males and can reproduce with others instead of themselves.
Many Cnidaria (AKA coelenterates) can both bud new individuals (asexual) or breed sexually.
Aphids can breed sexually or parthanogenetically.
Daphnia too.
Optional sexual breeding like this is often associated with breed fast and asexually when conditions are good, reproduce sexually when conditions are more harsh or the organism is stressed ( such as poor conditions for growth).

Several fish species have become parthanogenetic or can self fertilize, but they may be relatively new species. Some might say they are waiting go extinct when their environments change and they can not adapt.

Some rotifers (bdelloid rotifers) are thought to be fully parthanogenetic. They have survived for millions of years and even evolved new species. Without sex, it was a mystery how they did this.
Turns out they can dry out, get wet again and pick-up environmental DNA. This can result in horizontal transfer of genes (from other species) or replacement of one gene with another. This can provide they with different genes when needed for selection to choose among.
 
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I strongly second @Simon Bridge's argument about not self-fertilizing.

Although some species have dropped sex and reproduce parthanogenetically, self-fertilize, or clone themselves, they are thought to be limited in an evolutionary sense because their genetic diversity (as a population) is much more limited than sexually reproducing organisms.
Problems include: adapting to changing environments, evolve away from parasites, can't evolve new species because change is limited, can't easily get rid of bad mutations that they might acquire.

Even single celled yeast have mating types that require two different mating types to mate.

Some Exceptions:
Some worms can have a reproduce by self-fertilizing (Caenorhobditis elegans hermaphordite sex), but the species also has males and can reproduce with others instead of themselves.
Many Cnidaria (AKA coelenterates) can both bud new individuals (asexual) or breed sexually.
Aphids can breed sexually or parthanogenetically.
Daphnia too.
Optional sexual breeding like this is often associated with breed fast and asexually when conditions are good, reproduce sexually when conditions are more harsh or the organism is stressed ( such as poor conditions for growth).

Several fish species have become parthanogenetic or can self fertilize, but they may be relatively new species. Some might say they are waiting go extinct when their environments change and they can not adapt.

Some rotifers (bdelloid rotifers) are thought to be fully parthanogenetic. They have survived for millions of years and even evolved new species. Without sex, it was a mystery how they did this.
Turns out they can dry out, get wet again and pick-up environmental DNA. This can result in horizontal transfer of genes (from other species) or replacement of one gene with another. This can provide they with different genes when needed for selection to choose among.
If self-breeding were the problem, then why wouldn't that be eliminated by simple physical constraints? For example, if animals had both a penis and a vagina, they'd still have no way to self-fertilize because they couldn't physically inseminate themselves. So you'd just evolve very simple physical constraints on the placement of sexual organs that would preclude self-fertilization.

It seems more plausible to me that eliminating the need to have two sets of reproductive organs is the advantage of genders. Especially in ancient times where every scrap of energy was precious, not needing to grow both male and female organs would definitely be an advantage.
 
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jim mcnamara
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@Ygggdrasil - Yes higher plants especially plants often do have a "sex": monoecious, dioecious, and polygamodioecious. Long names, huh?

Monoecious - (one plant distinctly separate) male & female flowers on one individual. Which are incestuous I guess, except that in many cases pollen from plant A will not grow pollen tubes on any stigmas on plant A. The pollen is self sterile. - examples corn, pine trees

Dioeicious - plants have only male flowers, or only female flowers. - example Horticulturists try to plant only male Ginkgo trees because the do not make those messy fruits in the fall.

Polygamodioecious- mix and match. Some individuals of a single species are dioecious some are monoecious. Example maples. Some individuals make no fruit (the helicopter things, a samara), some have samaras only on a fraction of the tree, some are covered with them.

Parthenogenetic plants (and animals) do not interbreed with other individualsat all. Example - dandelions (Taraxacum)
 
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BillTre
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If self-breeding were the problem, then why wouldn't that be eliminated by simple physical constraints? For example, if animals had both a penis and a vagina, they'd still have no way to self-fertilize because they couldn't physically inseminate themselves. So you'd just evolve very simple physical constraints on the placement of sexual organs that would preclude self-fertilization.

It seems more plausible to me that eliminating the need to have two sets of reproductive organs is the advantage of genders. Especially in ancient times where every scrap of energy was precious, not needing to grow both male and female organs would definitely be an advantage.
There are aquatic organisms (cniderians, amphioxus, some fish) that release sperm and eggs to float free in the water and eventually find each other so they can fertilize. not too efficient, but they produce a lot of gametes (like millions). See the broadcast spawning section. The issues of fitting together don't arise in organisms like these.
 
  • #11
jim mcnamara
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@newjerseyrunner - there is no 'purpose' to sexuality. It evolved and was successful. Any definition of purpose we humans assign to it, is an ex post facto explanation to make us feel better. Meiosis became very selectively advantageous - meiosis is what sex is based on - because of recombination. It scrambles DNA. So a few of the the offspring can cope successfully with next year's or next century's changed environment.

There is no purpose to it. It worked, it won the Super Bowl of Natural Selection. So far. ...if you thrive on anthropomorphic explanations and sports, too.
 
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There are aquatic organisms (cniderians, amphioxus, some fish) that release sperm and eggs to float free in the water and eventually find each other so they can fertilize. not too efficient, but they produce a lot of gametes (like millions). See the broadcast spawning section. The issues of fitting together don't arise in organisms like these.
I'm aware of those kinds of animals, but I don't really see what your point is.
 
  • #14
BillTre
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I'm aware of those kinds of animals, but I don't really see what your point is.
Two points I guess:
1) External genitalia (which most people associate with gender) are not needed for sexual differences restricting who can breed with who.
2) Genetic sexual gender (or mating types or sexual reproduction) restrictions on breeding can exist without any kind of anatomical lock and key restrictions.

There is a very interesting fish, the Anableps or four-eye fish which is an unusual livebearing fish.
As livebearing fish (meaning birth little swimming fish rather than laying eggs), the male has to transfer sperm into the female.
It has been claimed that both sexes are sexually either right or left handed.
This intrigued me because if the handedness of their sexuality was genetically determined in both sexes, it could act as a reproductive isolation mechanism (only if right in one sex went with left in the other). Subsequent research indicates the handedness breeding restrictions are probably not 100%, so won't work.
This could have been an extreme case of an anatomical lock and key mechanism restricting breeding, but (in reality) probably not.

There are cases where anatomy is thought to restrict breeding possibilities.
 

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