What is the evolutionary explanation for having two sexes?

Andy asks: “What is the evolutionary explanation for having two sexes (man and woman)?” Thanks for the question, Andy!

Sexual reproduction began with simple single-cell organisms (eukaryotes). Since sexual reproduction provides much more genetic variation in a population than asexual reproduction does, it follows that species which could reproduce sexually were able to more quickly evolve in response to environmental changes than species that reproduce only asexually. It was therefore the asexual reproducers who were better able to develop into higher plant and animal forms.

6 Responses to What is the evolutionary explanation for having two sexes?

  1. Dale says:

    Hmmm…

    First – I have no problem at all with evolutionary theory.

    Second –

    It was therefore the asexual reproducers who were better able to develop into higher plant and animal forms.

    Don’t you mean (following your flow of thought) “It was therefore the sexual reproducers…”?

    Third- I have an honest question about your explanation.

    Since sexual reproduction provides much more genetic variation in a population than asexual reproduction does, it follows that species which could reproduce sexually were able to more quickly evolve in response to environmental changes than species that reproduce only asexually. [emphasis mine]

    Again, honest question here. I’m not seeing how increased genetic variation = increased evolutionary adaptivity. Asexual replication happens at a much faster rate, and is (obviously) a less complicated process than sexual reproduction… In a given environment and period of time, would not asexual replication provide a far greater number of replications and therefore the greatest ability to adapt? Does this not suggest that asexually-replicating organisms would be the most evolutionarily adaptive?
    Also, would there be intermediate ‘steps’ – and are there examples of intermediate species ‘on their way’ to being ‘sexual’ :)

    Fourth – I’m also interested in the evolutionary explanation for the step from single-celled organisms to multi-celled organisms.

  2. The Atheist says:

    Dale,

    Cheers. Yes, I did mean to say “sexual reproducers”.

    would not asexual replication provide a far greater number of replications and therefore the greatest ability to adapt?

    You are right that asexual reproduction occurs at a faster rate: 2 asexual specimens yield 4 offspring while 2 sexual reproducers (1 male and 1 female) yield only 2 offspring. However asexual reproducers don’t generate nearly the amount of genetic diversity (despite their faster reproduction rate) as sexual reproducers do. Each product of sexual reproduction has half the DNA of each parent so the possible combinations are virtually endless. Contrast this with asexual reproduction: each daughter is nearly an exact replica of its mother (except for rare defects during mitosis and rare defects due to radiation damage).

    Adaptation occurs when a particular set of traits is better suited for a change in the environment. A sexually producing population is likely to have much more diversity of traits than an asexually producing population. So it is more likely that some subset of individuals in a sexually reproducing population will possess traits which make them better suited to environmental change. Since individuals with the favorable trait are more likely to survive and reproduce than other individuals, the favorable trait becomes predominant in the population.

    Selection happens in asexually reproducing populations too and also because some set of traits is better suited to a change in the environment – but because asexually reproducing populations are more homogeneous, it is far less likely that a trait will arise which happens to be more suitable to the environmental change.

    Also, would there be intermediate ’steps’ – and are there examples of intermediate species ‘on their way’ to being ’sexual’ :)

    There are many plant species that reproduce both sexually and asexually. Plant lice can reproduce both sexually and asexually.

    I’m also interested in the evolutionary explanation for the step from single-celled organisms to multi-celled organisms.

    I find that quite fascinating too! This is a good summary with some equally good links to follow if you want more detail:

    http://en.wikipedia.org/wiki/Evolution_of_sex#Origin_of_sexual_reproduction
    http://en.wikipedia.org/wiki/Evolution_of_sex#Origin_of_the_Mechanisms_of_Sexual_Reproduction

  3. Bible Prophecy says:

    EVOLUTION: FACT OR FICTION?

    Charles Darwin hereby speaks for himself:

    “I may here also confess that as a little boy
    I was much given to inventing deliberate falsehoods,
    and this was always done for the sake of causing excitement.”

    Reference(s): The Autobiography of Charles Darwin 1809-1882. With original omissions restored. Edited by Nora Barlow. Page 23.

    See,
    http://darwin-online.org.uk/content/frameset?viewtype=text&itemID=F1497&pageseq=1

    “I love fools’ experiments.
    I am always making them .”

    Reference(s): John Bartlett (1820–1905).
    Familiar Quotations, 10th ed. 1919.

    See, http://www.bartleby.com/100/450.5.html

  4. Roel says:

    [quote]Andy asks: “What is the evolutionary explanation for having two sexes (man and woman)?”[/quote]
    Andy, don’t ask this to an atheist. Ask a biologist.

  5. Roel says:

    Andy asks: “What is the evolutionary explanation for having two sexes (man and woman)?”

    Andy, don’t ask this to an atheist. Ask a biologist.

  6. discount barbours jackets

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: