What is the unit to use in evolution?

  1. And what are some good examples besides humans?

    I'm guessing that years don't matter as much as generational cycles.

    edit: for example, how many evolutionary cycles for humans would be contained in 100 years? Or dogs? Do you count by total age or reproductive age?
    Last edited: Jan 5, 2013
  2. jcsd
  3. Evo

    Staff: Mentor

    PLease explain what you mean by "evolutionary cycles" and "units to use in evolution".
  4. Evo

    Staff: Mentor

    I need vjk2 to explain what they mean before anyone posts so we don't go off on tangents.

    Last edited: Jan 5, 2013
  5. Well, I'd guess it would be something like change per generation. How to define either characteristic is up in the air, though generation seems basically like the average age before reproduction occurs in a species. I wonder how to take into account the range of ages. A woman can reproduce from like ages 12/13 to like 50, while men can reproduce pretty much well into their 70's and 80's.

    There is the Evolutionary Significant Unit which is a subpopulation that is considered distinct from the larger species.
  6. Evo

    Staff: Mentor

    You seem to have some basic misunderstandings about evolution.

    Puberty usually decides when a person id adle to reproduce, except where puberty happens too early, the chances of a pregnancy lasting to full term is unlikely for a number of reasons. This is not evolution. How long a person remains reproductive from one generation is not evolution.

    Please explain what you wish to know about this.

  7. atyy

    atyy 11,190
    Science Advisor

    Yes, the generation time is a parameter in models of evolution. The first reference by Hobolth is an example of this. Because of the range you mentiond, one needs some sort of average. But what sort of average? Some of the problems are discussed in the second and third references. (In the PubMed links, there are links to free versions of some of these articles at the top right of the page)

    Hobolth A, Christensen OF, Mailund T, Schierup M. Genomic relationships and speciation times of human, chimpanzee, and gorilla inferred from a coalescent hidden Markov model. PLoS Genet. 2007 Feb 23;3(2):e7.

    Tremblay, Vezina. New estimates of intergenerational time intervals for the calculation of age and origins of mutations. Am J Hum Genet. 2000 Feb;66(2):651-8.

    Kim SH, Elango N, Warden C, Vigoda E, Yi SV. Heterogeneous genomic molecular clocks in primates." PLoS Genet. 2006 Oct 6;2(10):e163.
    Last edited: Jan 5, 2013
  8. Ygggdrasil

    Ygggdrasil 1,825
    Science Advisor

    You are correct that generations are the relevant unit of time when considering evolutionary change. For example, mutation rates are generally measured in terms of mutations per generation. This occurs, of course, because the gene pool of a population cannot change until the current generation breeds and passes on a subset of its genes to the next generation.

    As for how long a generation is, it is the age until reproduction. So, for humans this is on the order of 20 years (rather than human lifespan, which is a larger period of time). For studies of evolution in microorganisms (such as bacteria), we usually use the doubling time of the culture as the length of one generation. Note that the length of one generation can change over time (for example, as a culture of bacteria adapts to its environment its doubling time will decrease as replication becomes more efficient).
  9. Evo

    Staff: Mentor

    Evolution does not happen within one generation, which may be confusing, yes it is generational, for humans it is slow and with no guarantee the trait will survive.

    It also appears that generations are now between 30-35 years. I am trying to pull up the link, but the forum's viglink service is blocking me.
    Last edited: Jan 5, 2013
  10. Ygggdrasil

    Ygggdrasil 1,825
    Science Advisor

    Thank you for the clarification, Evo. I certainly did not mean to suggest that any significant changes to the gene pool can occur in one generation. Most changes to species or traits occur over very many generations (for example, in the Lenski long-term evolution experiment, the ability to metabolize citrate evolved after 31,500 generations).

    Although 30-35 years may be the current human generation time, generation times were almost certainly shorter than that throughout most of human evolution.
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