Evolutionary biology News

We still don’t know why sex exists, and we have the theories to prove it

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Further to: Another whack at the “sex paradox” (The truth is, after much study, we still don’t know why sex exists in life forms.), here’s an open access 2012 article, evaluating the many hypotheses in more detail:

Hartfield, M. and Keightley, P. D. (2012).

Current hypotheses for the evolution of sex and recombination.

Integrative Zoology 7: 192-209.

Abstract: The evolution of sex is one of the most important and controversial problems in evolutionary biology. Although sex is almost universal in higher animals and plants, its inherent costs have made its maintenance difficult to explain. The most famous of these is the twofold cost of males, which can greatly reduce the fecundity of a sexual population, compared to a population of asexual females. Over the past century, multiple hypotheses, along with experimental evidence to support these, have been put forward to explain widespread costly sex. In this review, we outline some of the most prominent theories, along with the experimental and observational evidence supporting these. Historically, there have been 4 classes of theories: the ability of sex to fix multiple novel advantageous mutants (Fisher–Muller hypothesis); sex as a mechanism to stop the build-up of deleterious mutations in finite populations (Muller’s ratchet); recombination creating novel genotypes that can resist infection by parasites (Red Queen hypothesis); and the ability of sex to purge bad genomes if deleterious mutations act synergistically (mutational deterministic hypothesis). Current theoretical and experimental evidence seems to favor the hypothesis that sex breaks down selection interference between new mutants, or it acts as a mechanism to shuffle genotypes in order to repel parasitic invasion. However, there is still a need to collect more data from natural populations and experimental studies, which can be used to test different hypotheses.

Key words: evolution of sex, fitness-associated sex, Hill–Robertson interference, mutational deterministic hypothesis, Red Queen hypothesis

Hat tip: Pos-Darwinista

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12 Replies to “We still don’t know why sex exists, and we have the theories to prove it

  1. 1
    ScuzzaMan says:

    For me, the obvious question is, do non-sexually reproducing organisms have any of these ‘problems’ that sex supposedly solves?

    I dont know, but it would seem a question worth asking.

    If they don’t, then … ?

  2. 2
    News says:

    ScuzzaMan, it’s possible that sex relates mostly to complexity, because it seems to predominate among more complex life forms. I hope someone will write in to correct me if I am wrong, but among those life forms thought to have intelligence (cephalopods, ravens, wolves, primates), it is universal or nearly so.

  3. 3
    Andre says:

    Well since materialism can’t answer this maybe the biblical answer is good enough for me since I consider God as the author of sex…..

    Genesis 1:28 “And God blessed them. And God said to them, “Be fruitful and multiply and fill the earth and subdue it and have dominion over the fish of the sea and over the birds of the heavens and over every living thing that moves on the earth.”

    But this is of course in contrast with the materialist view that we are too many……

  4. 4
    awstar says:

    In this review, we outline some of the most prominent theories, along with the experimental and observational evidence supporting these. Historically, there have been 4 classes of theories: the ability of sex to fix multiple novel advantageous mutants (Fisher–Muller hypothesis); sex as a mechanism to stop the build-up of deleterious mutations in finite populations (Muller’s ratchet); recombination creating novel genotypes that can resist infection by parasites (Red Queen hypothesis); and the ability of sex to purge bad genomes if deleterious mutations act synergistically (mutational deterministic hypothesis)

    I wonder if these who call themselves scientists knew how they come across as atheistic religious bigots, if they would include a sixth explanation based on ID. namely; sex was intelligently designed for their happiness and the species benefit (Jesus Christ hypothesis)

    “And he answered and said unto them, Have ye not read, that he which made them at the beginning made them male and female, And said, For this cause shall a man leave father and mother, and shall cleave to his wife: and they twain shall be one flesh? Wherefore they are no more twain, but one flesh. What therefore God hath joined together, let not man put asunder.” Matthew 19:4-6

  5. 5
    Chalciss says:

    How can sex exist for those that deny “self” exists? 😉

  6. 6
    tjguy says:

    Here we face the limitations of true science. Science can examine sexual reproduction today and learn how it works, what the benefits are to sexual reproduction.

    ID and creationism purports that it is designed that way so we too believe there must be benefits to sexual reproduction or else the Creator would not have created us this way.

    Setting aside human sexuality which has purposes that don’t apply to the animal kingdom such as unity(the two become one, expression of love, etc.), sexual reproduction obviously works and has persisted all this time so there must be some benefit to it.

    So we agree with the evolutionists on this. There must be some benefit to it, but that said, simply finding a benefit to it has nothing to do with how it evolved or even IF it evolved. Those are two separate issues.

    It could have a benefit and purpose and still have been created that way as opposed to having evolved. SO finding a purpose does not necessarily tell us how or why it evolved. Evolutionists may want to believe that, but logically speaking, it doesn’t work.

    Again, there are certain things that science can tell us and other things that science cannot tell us.

    Why sex exists seems to be something that if we learn enough about the process, we might be able to come up with some good reasons, but it is interesting to see that evolutionists still haven’t settled that question. Even that may be a question that is hard to really nail down scientifically speaking, but it should be easier to answer than how it came to be. That is a question that science cannot answer.

    Did it evolve or not? Can science really answer this definitively? I don’t think so.

  7. 7
    Acartia_bogart says:

    Scuzzaman:

    For me, the obvious question is, do non-sexually reproducing organisms have any of these ‘problems’ that sex supposedly solves?

    If we define sex as the sharing of genetic material between two individuals, then I am not aware of any organism that does not do this. Even bacteria swap genetic material.

    All protozoans have a sexual phase, and animals we commonly think of as parthenogenic, also have a sexual phase. I am not sure about bacteria, but for single celled eukaryots and metazoans, if they do not undergo a sexual phase every now and then, the line senesces and dies. So, obviously, this reshuffling of genetic material is critical. But it is interesting to note that this sexual phase need not involve the swapping of genetic material with another organism. Many ciliates undergo autogamy, which involves the cell undergoing meiosis and then recombining with itself. For some reason, this will also rejuvenate the line.

  8. 8
    Acartia_bogart says:

    Awstar:

    sex was intelligently designed for their happiness and the species benefit (Jesus Christ hypothesis)

    Does this mean that a paramecium can feel happy?

  9. 9
    tjguy says:

    AB,

    Does this mean that a paramecium can feel happy?

    When the Bible speaks of sex, it does so in relation to humans, not to animals. Through sex, a male and a female become one. Sex serves the very important role of helping to unify a married couple. It certainly contributes to the happiness of humans, but it also is a way of showing love to our spouses. The Bible speaks of sexual intercourse using the term “know”. So Adam “knew” his wife and she became pregnant. It is a way of deepening a relationship and helping married couples reach the oneness that God intends for a married couple.

    None of this has to do with animals. For animals, (paramecium included), sex is basically to reproduce. There is no love involved – either giving or receiving, no unity, no meaning outside of reproduction.

    Animals have no restrictions on sex. Only humans. Sex was designed to be a blessing to us, but wrongly used, it can also bring much unhappiness. Sex was also created as a means of fulfilling God’s creation to “fill the earth”.

    Sex helps to keep a couple close together. If they want to have sex, they need to keep their relationship close, learn to forgive, and to be kind to each other. Animals have no need of this. It is purely a physical act for them.

    There is a huge difference between animal sex and human sex – or at least there should be.

    Humans who pursue sex like animals become slaves to their passions. Sex minus love is reduced to a mere physical act that doesn’t satisfy anyone. Sex alone, does not lead to happiness.

  10. 10
    Acartia_bogart says:

    Tjguy, what does your comment #9 have to do with the evolution (or design) of sexual reproduction and its ubiquitous nature?

  11. 11
    Dionisio says:

    tjguy

    Humans who pursue sex like animals become slaves to their passions.

    Check this out:

    http://www.theguardian.com/boo.....iew5/print

  12. 12
    PeterJ says:

    However it came to be, these guys were supposedly the first to get at it. Then everyone else simply followed suit 😉

    http://www.bbc.co.uk/news/scie.....t-29661446

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