Evolution debate links IB Biology concepts

Friday 2 August 2019

In recent years a debate about standard evolutionary theory has taken place amongst Biologists. Any sign of disagreement among scientists can be interpreted as a weakness of the theory of evolution, when actually it is a strength. IB students who know about the nature of science understand this. Theories help us to understand data and new pieces of evidence help us to modify and improve theories.

Teachers encourage students to read about Biology in the news, but in my experience very few students make time for this during their IB diploma course. Choosing the right articles might help. Where there is conflict the reading becomes more interesting.  If the content of IB Biology helps students to understand the disagreement, even better.

In this example the conflict occurs between supporters of the Standard Evolutionary Theory and supporters of a new model called, "Extended Evolutionary Synthesis".  The biologists promoting the extended synthesis model claim that the standard theory of evolution is too simplified and that it doesn't represent the fullness of our understanding.  It is a great example of something which IB Biology students should read about outside of lessons.
It illustrates the connected nature of biological ideas and includes some really counter-intuitive biological examples so it is well worth the effort to read. So what is it all about? Extended evolutionary synthesis is a new approach to standard evolutionary theory.

Strange examples which support Extended evolutionary synthesis:

  • Centipedes always have an odd number of pairs of legs. No species of centipede could ever have one hundred legs! [1]
  • Mice conditioned to fear almonds give birth to almond fearing mice. They seem to inherit learned behaviour! [2]
  • Locusts change their behaviour, from placid solitary animals to swarming masses, in response to population density.
    Extended evolutionary synthesis combines four modern discoveries which have effects on evolution: developmental bias, phenotypic plasticity, niche construction, and extra-genetic inheritance.
    1. Phenotypic variation is not always random but rather mechanisms such as developmental bias help to privilege certain phenotypes. The mechanism by which centipedes grow causes them to always have an odd number of pairs of legs. No species of centipede could ever have one hundred legs!
    2. Phenotypic plasticity refers to the way certain organisms can directly alter their morphology, physiology, and behaviour in response to an environmental change.  Locusts change from solitary animals to swarming masses.
    3. Niche construction illustrates that organisms do not passively adapt to their surrounding environment through the survival of the fittest but will actively alter that environment so that it is often more hospitable for them and their descendants. Beavers and earthworms are two examples
    4. Epigenetics is the field that looks at “the heritable changes in gene expression (active versus inactive genes) that does not involve changes to the underlying DNA sequence; a change in phenotype without a change in genotype.” Extra-genetic factors (DNA methylation, histone modification, and non-coding RNA) influence the underlying DNA’s expression. What is more, these epigenetic markers can be influenced by environmental and behavioural patterns and can be transmitted to progeny up to two to three generations. Mice conditioned to fear almonds give birth to almond fearing mice.

    IB Biology students could be asked to read one of the articles after a lesson on genetics, ecology or evolution.

    Interesting references, suitable for IB Biology students.

    1. Fascinating facts about centipedes: https://www.thoughtco.com/fascinating-facts-about-centipedes-1968228
    2.  Evolution unleashed: Mice conditioned to fear almonds give birth to almond fearing mice: Aeon Magazine: https://aeon.co/essays/science-in-flux-is-a-revolution-brewing-in-evolutionary-theory   [Audio file of the article too]

    3. Scientists Seek to Update Evolution: Quanta magazine: https://www.quantamagazine.org/scientists-seek-to-update-evolution-20161122/

    4.  The changing face of Evolutionary theory: Biologos: https://biologos.org/articles/the-changing-face-of-evolutionary-theory


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