Natural Selection: asexual, sexual, and unisexual

whiptail lizard1

 

Reproduction among the animal kingdom appears to be a hit-and-miss proposition. Even evolutionary biologists cannot come to one accord on a given direction with natural selection. Throughout the history of science sexual reproduction – the fertilization of the egg by sperm – has predominantly been considered status quo. However, early in the twentieth century scientists began noticing unisexual species, and further discoveries included asexual species to the growing list. In fact, in less than one hundred years there is now a list of over fifteen-hundred nonsexual species recorded.

The initial assumption arrived at by the majority of researchers in the biological field was that they were seeing the beginning of natural selection paving the way for the next evolutionary step in the reproduction of species. But was that truly the case? They thought so at first, after the initial fifty or so discoveries. But as the number of species elevated rapidly that hypothesis no longer seemed to hold up. Furthermore, technology improved, which played a role in many of the initial discoveries. And as technology continued to progress biologists realized that evidence seemed to suggest some of the nonsexual species they had found, along with species that reproduced both sexually and nonsexually, were hundreds of thousands of years old: with several they even believed to be as much as two-million years old.

Species that were hundreds or a few thousand years old were considered too young, by evolutionary biologists, to have seen a complete evolutionary change in their sexual reproduction. But the older species tore apart the belief that natural selection had only recently (in evolutionary terms) begun to make the next major evolutionary leap in animal reproduction.

I am not quite sure I agree with that initial hypothesis. After all, Darwin recorded noticeable evolutionary changes in certain species (like the finches) from one generation to the next as a result of the change in available food supply. There has also been a wide variety of recorded information in the past fifty years showing species in controlled environments going from sexual to unisexual, and sexual to asexual species in one or two generations. However, some species fail to mutate in controlled conditions, while others mutate sporadically with as little as one-to-six percent transforming. And yet, other species have shown one-hundred percent mutation in a single generation: and their offspring reproduced without sex… though some species still needed fertilization of the egg, but without the sex act.

The result of the diverse findings has led to a hodge-podge of beliefs. No one has come up with anything close to a universal hypothesis to explain the absence of uniformity in animal reproduction.

Most evolutionary biologists question the need for sexual reproduction: “If reproduction can occur without sex, why does sex occur at all?” (Johnson, 2012) One train of thought contends that there appears to be an inevitable limit to long-term species survival inherent in clonal reproductions (Johnson, 2012). It is a phenomenon known as the ratchet mechanism, or Muller’s Ratchet, after Noblest Herman Muller, in the early sixties (Simon et al 2003).

Another contention, called the Red Queen Hypothesis, asserts that there is an instant advantage with sexual reproduction in producing genetically diverse offspring that make it tough to be targeted by harmful parasites (Simon et al 2003). This hypothesis was tested using Crucian Carp: the diploid sexual had fewer parasites than the triploid gynogens (cited in Simon et al 2003).

A third contention is known as the DNA Repair Hypothesis. Various geneticists believe sex continues because “only a diploid cell can effectively repair certain kinds of chromosome damage,” (Johnson 2012), primarily double-strand breaks in DNA. They suggest that synapsis “which in early stages of meiosis precisely aligns pairs of homologous chromosomes, may well have evolved originally as a mechanism for repairing double-strand damage to DNA” (Johnson 2012).

After reading up on the abundant variations of asexual and unisexual, along with the equally diverse methods of research, I came away with far more questions than answers. One of the biggest problems I saw in the research is that there is no standard methodology for studying or recording the information and data acquired. It is impossible to arrive at a universal answer to the basic ongoing questions when every scientist and research group alters their methodology to accommodate their resources, and often their hypothesis. For instance, certain scientists I read about confirmed that specific species have had no known mutations in sexual reproduction in their natural environment. But that did not stop them from isolating the species in a controlled environment to force mutation: and even after the forced mutation the mutated species never took hold in the natural habitat after they released it into its known environment.

Similarly, there are examples of natural mutation that have failed to show identical results in controlled settings. This raises additional questions of validity with regards to natural selection. How many of the alleged fifteen-hundred-plus asexual and unisexual species have honestly been naturally selected or genetically mutated (engineered) by humans? Which creates another question in a similar vein: how much of the human pollution, and toxic or nuclear waste, has added to the mutation level in the natural environments of many of these mutated species?

For instance, I know of several areas, such as dams and reservoirs, where the fish, fowl, and other local species have shown dramatic mutation in size, appearance, and behavior. Yet, not once in all the examples of research into mutated species on sexual reproduction that I have read did the scientists consider unnatural or external elements in the species natural environments a possibility  for mutation: to prove or disprove. That seems highly unprofessional, and yet it is the standard practice (as far as I can tell), to automatically discard the possibility of something that has been confirmed many times over, in many areas, simply because it does not fit their initial hypothesis.

Instead of learning what I hoped to learn while researching this paper, all I ended up discovering was my distrust for the recorded findings. So much of the methodology proves more about the genetic manipulation by humans with career aspirations than it does about natural selection. I admit that I am not a geneticist or evolutionary biologist, and will never be. But I was an investigator for many years, and I know a lot about eliminating suspects (or non-truths) to get at the right culprit (or truth). And as I read the research, if I only looked at the alleged data (like the proverbial tree) it seemed valid, but when I looked at the big picture (like the proverbial forest) all I saw was a lot of window dressing to validate their hypothesis in order to keep their grants coming in: there are just too many unanswered questions and areas never considered.

 

References

American Museum of Natural History. (2012). Web.

Johnson, G. (2012). The Living World. McGraw-Hill, NY. (180-181).

Patrusky, B. (1982). Where Males Don’t Count. Mosaic. (2-8).

Schlupp, I. (2005). The Evolutionary Ecology of Gynogenesis. (399-412).

Simon, J., Delmotte, F., Rispe, C., and Crease, T. (2003). Phylogenetic relationships between parthenogens and their sexual relatives: the possible routes to parthenogenesis in animals. Biological Journal of the Linnean Society (151-163).

 

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9 thoughts on “Natural Selection: asexual, sexual, and unisexual

  1. alphajt June 2, 2017 / 4:48 pm

    I love this, JW. You dig beyond what they want people to hear and see the gaping flaws in the methodology.

    Liked by 1 person

    • jwtatfbc June 2, 2017 / 5:00 pm

      Too many theories are pushed like mechanical lemons by used car salesmen. Taking things at face value can often leave you with costly surprises in the end. Thanks, AJT.

      Liked by 1 person

      • alphajt June 2, 2017 / 5:10 pm

        Absolutely!

        Liked by 1 person

  2. MC Clark June 2, 2017 / 9:19 pm

    Interesting article, JW. Seems as if scientists may have something in common with politicians–each skewering the facts to fit their own personal agenda.

    Liked by 1 person

    • jwtatfbc June 3, 2017 / 3:08 am

      You’re very welcome. Thank you for the response.

      Like

  3. poeturja June 4, 2017 / 6:53 pm

    Fascinating post, especially the dilemma of the blessing and curse of the funding grant…

    Liked by 1 person

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