Monday, April 5, 2010

What's the deal with sex?

Many organisms reproduce by means of sex. They find a companion, or the opposite sex, and mate. However, there are also female organisms that can reproduce "parthenogenetically" (155). This means that the female just produces eggs that can fully develop without being fertilized. Parthenogenetic reproduction is much less energy intensive because there is no need to find a mate and would also cause to a decreased need of ornate (and possibly detrimental) physical characteristics in sexual dimorphism. And females would be able to produce twice as many parthenogenetic offspring because all would be female and able to reproduce alone. But we know that sex is the most common means of reproduction. Why is this? If parthenogenetic reproduction costs less energy, why don't parthenogenetic organisms outcompete sexually reproducing organisms? A rise in parthenogenetic reproduction would make males obsolete. What would happen if this happens?


  1. Great question, Brion! To get started with this question I’d like to quote Salt N Peppa and say “Let’s talk about sex baby!” : - )

    Sexual reproduction is the most common means of reproduction, and this is because it is the most efficient way to reproduce in order to ensure efficient survival and reproduction of the organism and species. A study performed by Maurine Neiman, the assistant professor of biology in the UI College of Liberal Arts and Sciences experimented with freshwater snails. She says that although sexual reproduction requires more time and energy, it is much more common among living organisms, and, therefore, must be beneficial ( After experimenting and comparing asexual versus sexual reproduction in the New Zealand freshwater snail, she determined that “sexually reproducing snails had accumulated harmful DNA mutations at about half the rate of the asexual snails” (Neiman).

    A more obvious advantage to this sexual reproduction is that in sexual reproduction two separate sets of DNA, one from each parent, are fused together to form a new gamete. These gametes have an infinite number of possibilities creating a diverse population. A species with a lot of variation has an advantage in that it is much less susceptible to any one kind of attack ( A threat would not wipe out an entire population because every organism is not exactly the same. Only the strong would survive and the species as a whole would adapt to meet the changes brought on by the threat. It is because of this selective advantage that parthenogenetic organisms do not out compete sexually reproducing organisms.

    If the population of men became obsolete, then there are some options as to what would occur to the population of the species. If the women do not evolve through natural selection to be able to mate with themselves, then the entire species would die off. If there are no men for the women to mate with, then no mating would occur which would lead to either a dramatic decline in the population or the extinction of the species.

    On the other hand, if the women in the population became (or were) parthenogenetic, then the species could live on. However, because the species would be lacking the selective advantages of having a sexual reproduction (those advantages are shown above in the response), it would be more difficult to defend from threats such as parasites and bacteria. If a new disease arises, it would put the species at risk for extinction, which would most likely send it down the extinction vortex that endangered species spiral down ( Therefore, sexual reproduction is more advantageous, which is the reason why most organisms exhibit sexual reproduction.

  2. Parthogenetic reproduction has been seen in some fish, insects, frogs and lizards. In the lab rats have even been manipulated to reproduce using this method that requires no mate and no sexual interaction. While organisms are driven to survive and reproduce and this parthogenetic reproduction method is efficient by producing twice as many offspring without needing to find a mate it completely blocks out genetic diversity, a very important part of life as we know it. Parthogenetic reproduction has its place in nature as a mechanism that can be used in times of need. Such as avoiding spreading a bacteria to further generations or in the case of the Komodo female dragon it switches on when there is no male to mate with. This type of reproduction is only used in such small quantities compared to sex because we need genetic diversity. Genetic diversity allows genes to mix and match so that natural selection and evolution itself can continue. The changes that are made in order for an organism to adapt to its environment are made when genes mix together from the combination of two organisms, the identical organisms that are produced with parthogenetic reproduction leave no room for adaptation and natural selection would no longer occur and evolution would not continue in the beneficial way that it has for billions of years.

    For example, parasites that evolve to find new ways to infect a species would demolish that species if it reproduced parthenogenetically because it would not be able to evolve a way to counteract the parasites new way of attack and form a new form of defense quick enough. Therefore a parthenogentic reproduction would cost the organism less energy but due to adaptations the other sexually reproducing organisms can make the parthenogentic organisms do not outcompete them.

    If parthenogenetic reproduction rose and males were made obsolete then there would a slow in the process of evolution. The females that occupy the planet would have many companions that were identical copies of one another. The population would move towards a more and more homogeneous state. Social customs would clearly change. Fighting over the remote would decrease significantly and everyone would be comfortable pulling over and asking for directions.

  3. There is one reason why sex is the most common form of reproduction, and that is because there is a higher chance of generating adaptations. Whether these adaptation would be good or bad adaptations. Genes are passed down from person to person. Through sex, parents are able to give up half their genes to their offspring. It provides for genetic diversity. That is the point of sex. You are suppose to mate in order to spread your genes. We are a different creatures from chickens. We were meant to choose the best possible mate to create the most favorable offspring. By creating this diversity, we have a higher chance of natural selection choosing traits that would be favorable to the human race. These traits would prob be favorable to us. I agree with Ryan on one point and that is that it will enhance our survival. That is because by choosing good mates people will be able to survival longer through the genes they inherit, and because of the adaptations that they will obtain. The human race would always live because certain people will have the genes in order to survive. We don't want to have identical copies of us running around. We want diversity, and with diversity brings new ways to cope with diseases and other thing that harm us.
    They don't out compete us because we have the tools necessary for survival. We have the ability to have offspring, and every animal is. Sexually we transfer genes to help an organism survive better. If an animal just keeps on reproducing parthenogenetically, then there would be no way for them to develop immunity to certain diseases.
    If there was a rise in parthegenetic reproduction, the males would become obsolete, and the females would become the only source living. This would cause no diversity in our planet, and natural selection might not even take place. They would have no means of developing adaptations that would enhance the survival of the species.


  4. Yeah, but why You guys say that there will not be genetic diversity? I mean, there is a theoretical possibility that male humans may become extinct due to y chromosome deterioration. But, if that happens, women will start using lab derived parthenogenesis which means either injecting haploid nucleus into another women's egg or either creating female sperm from female stem cell and them fertilising another woman's egg. Ofcourse we can't do that with today level of reproductive medicine, but in so much distant future would you bet we won't be able to do it? So basicallly, those girls will have two moms so they won't be clones! That's actually not parthenogenesis, it's a form of artificially simulated sexual reproduction! Genetic diversity of the population would remain like todays even if males are absent!