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Welcome to Evolution and Biodiversity (BIL 160)

"Nothing in biology makes sense except in the light of evolution."

-- Theodosius Dobzhansky

An informal poll: Which is the most highly evolved species?

  • EVOLUTION is defined as change over time.
  • ORGANIC EVOLUTION is the genetic (and phenotypic) change of living organisms over time.

    We are the products of our ancestors' choices.

    Another poll, this one with three parts.

    Now the big question...why?

    Common Misconceptions About Evolution

  • MISCONCEPTION: Evolution is "only a theory".
  • MISCONCEPTION: Evolution describes the origin of life on earth.
  • MISCONCEPTION: Evolutionary theory implies that life evolved, and is evolving, by chance.
  • MISCONCEPTION: Evolution is progress: evolving organisms are getting better.
  • MISCONCEPTION: Individual organisms evolve during their lifetimes.
  • MISCONCEPTION: Evolution occurs only gradually, over very long periods of time.
  • MISCONCEPTION: Species are distinct natural entities that can be clearly defined and recognized.
  • MISCONCEPTION: Genetic drift occurs only in small populations.
  • MISCONCEPTION: Our species is no longer evolving.
  • MISCONCEPTION: Because evolution is slow, humans cannot influence it.

    Evolution and Biodiversity

    The Convention on Biological Diversity defines biodiversity as

    Biodiversity is the variety of living species on earth.

    Depending on the source, anywhere from 1.2 to 1.7 million species of eukaryotes have been cataloged and described in a scientific paper (i.e., been physically described and given a scientific name in a refereed, scientific journal journal).

    Other sources put the total closer to 2 million.

    More than half of animal species are insects, with more than 300,000 described species of beetles alone!

    Plants are also diverse.

    But the 1-2 million species known to science does not likely approach the actual number of species on earth.

    Eminent natural historian and philosopher Edward O. Wilson has estimated that there may be 5 - 50 million species of eukaryotes on earth. Others have suggested there may be even more.

    And we haven't even considered the massive number and diversity of prokaryotes:
    Approximately 5 x 1030 (that's five million trillion trillion--a five with 30 zeroes after it) bacteria and archaeans share the planet with us.
    (A stack of this many pennies would be a trillion light years long.)

    Systematics and Taxonomy

  • A biologist who names and classifies living things is known as a taxonomist.

  • A biologist who studies the evolutionary relationships between living organisms is a systematist.
    (Most systematists are also taxonomists.)

    Systematics Vocabulary

    How Much Genetic Variety Are We Talking About?

    Recall that the genome is the full DNA sequence of an organism.

    A diploid organism has two copies of its genome in each of its diploid cells, one from each parent.
    The two copies are not necessarily identical.

    In eukaryotes, we must distinguish the

    The number of genes in a genome depends on the species. Numbers range from about 1000 (in a typical bacterium) to more than 400,000 (in some ferns and flowering plants).

    Mammalian genomes are still being quantified, and differ across species.
    The human genome is believed to contain fewer than 20,000 protein-coding genes.

    How much information is that? Let's consider a hypothetical eukaryote with 100,000 nuclear genes.

    Biodiversity is Disappearing

    Most species that have existed on earth are now extinct.

    But the rate of extinction currently going on qualifies as a mass extinction similar to large-scale loss of species that have occurred only a few times in the earth's past.

    Currently, the main causes of loss of species can be traced back to one very successful species, Homo sapiens, that has caused and is now causing Loss of Biodiversity (H.I.P.P.O.):

    Let's not forget the effects of anthropogenic (human-caused) climate change

    Why Should We Care?

    Of what value is all this species variety? Let's consider one problem, loss of genetic diversity.

    We're all aware that in most human societies, there are taboos against inbreeding Because relatives are more likely to share genes in general, they are also more likely to share deleterious (harmful) alleles of certain genes, as well.

    Mating between close relatives increases the likelihood that such alleles will be inherited in homozygous condition by their offspring.

    If the alleles are recessive (which is often the case with deleterious alleles, since dominant ones usually don't last long in a natural population), the harmful condition is more likely to be expressed.

    Many well-known genetic disorders in humans are due to the inheritance of two recessive alleles, and is often due to some degree of mating between relatives (even if they are distant relatives from the same ethnic group). name just a few.

    The smaller the size of a wild population, the more genetically uniform it will be, and the more likely there will be inbreeding.
    As a species becomes rare, it is more likely to undergo inbreeding and express harmful genetic conditions.

    This is also demonstrated by human artificial selection to produce "desirable" characteristics in domestic animals and plants by inbreeding them. Unfortunately, less desirable alleles of other genes may also come along for the ride, and their expression is more likely in highly inbred cultivars (plants) and breeds (animals).

    This phenomenon is nicely illustrated by purebred dogs.

    A Paucity of Domesticity

    Although there are millions of species on earth, humans have managed to domesticate (or semi-domesticate) relatively few of them. The combination of few domestic species produced and refined by inbreeding can set the stage for economic disaster.

    The Saga ofZea mays: domestic corn

    In the mid 1970's highly inbred Zea mays crops in the U.S. were attacked by an extremely virulent viral blight that threatened to completely wipe out these economically vital crops.

  • With little genetic diversity, crops were dying to the blight. They had no genetic resistance to it.

  • A team of biologists working in Western Mexico to catalog species discovered a one hectare stand of a previously unrecognized wild cousin of Zea mays:

    (on the right, a wild cousin of maize,
    on the left, maize,
    and in between, their F1 hybrid).

    It was located in an area that was being logged out to be replaced by cattle pasture.

  • Zea mays (2n=20)
  • A close relative, Zea perennis (2n = 40) - can't hybridize
  • This new relative, Z. diploperennis (2n = 20)
  • The new species was hybridized with domestic corn.
  • Breeding the two had two potential benefits:
  • Viral resistance is among the dominant alleles passed on by the wild corn.
  • A personal account can be found here, as told by Dr. Hugh Iltis.

    Similar scenarios have played out several times in other domestic crops.

    Losing wild species means losing the genetic "safety net" they provide.

    Wilderness as a resource

    There are several different ways that humans may view the value of wild species.
  • anthropocentric view: non-human species are important only in so far as they can benefit humans (e.g., provide products such as food, medicines or other commodities)

  • biocentric view: non-human species are important to save for their own, intrinsic value.

  • ecocentric view: biodiversity and ecosystems should be preserved--not just individual species or populations--because it is the whole, working system that maintains diversity.

    Disassembling ecosystems would be like disassembling a human body: the component parts don't function individually the way the whole does.

    Ecologically significant species

    Politically significant species

    Note that one should use great caution when defining threatened and endangered species.

    And always remember the Universal Laws of Endangered Species:

  • "There are only about 30 left"
  • "They taste like chicken"

    Over the course of the next 14 weeks, we will be studying species in the context of evolution. This is a term that's been in the news a lot lately. So before we even embark on our journey, let's have a little Word about Science....

    Biology is a Natural Science

    The difference between a Miracle and a Fact
    is exactly the difference between a mermaid and a seal.

          -- Mark Twain
    The Natural Sciences (Physics, Chemistry, Biology, Geology, etc.) are governed by the necessity of their adherents to utilize

    The Scientific Method add to the knowledge of their field.

    As you should know by now, the scientific method is a precise set of rules followed by researchers/investigators in the natural sciences.

    If you're not sure you recall, then Review the Scientific Method here. (You'll be responsible for knowing this on an exam, and in your future life as a professional science person.)