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Epigenetics: How Evolution Is Evolving

By Andrew Howley

Ever since the 1940s, the “modern synthesis” has presented evolution as the result of random mutations to DNA creating altered versions of living creatures that live and reproduce or die childless based on how well they happen to fit into their environment. This idea has served well in many ways for the generations since then, but now there’s a new kid in town.

Meet the “New” Kid

“Epigenetics” addresses the increasing evidence that things other than DNA can control the appearance and function of living things, can be passed on to future generations, and most importantly, can arise in direct response to external environmental conditions. It’s been covered in Science and TIME, on NOVA, Science Daily, and in an exposé-like series of articles from Scoop.co.nz.

This means that scientists should make room in the pantheon next to Darwin for the often ridiculed “stretch-your-neck-to-become-a-giraffe” Lamarck, who proposed that organisms change throughout their lives and pass on acquired traits to their offspring.

A closer look at history shows we also need to make a little more room next to Darwin for… Darwin himself.

The modern synthesis included certain of Darwin’s theories, but discarded others, including that of “pangenesis,” his idea that each body part somehow contributes “gemmules” of information to the sex cells to pass on traits acquired through use or disuse in the parent’s life (read Darwin’s “Provisional Hypothesis of Pangenesis”).

darwin-illustration-collage.jpg

An illustration of Charles Darwin and natural forms that inspired his theories, from the September 1976 National Geographic magazine.

Tiny Prions, Major Changes

Recent work is showing that Darwin was more correct than he’s been given credit for. In “Epigenetics in the Extreme” from the October 29 Science magazine special issue on epigenetics, Randal Halfmann and Susan Lindquist discuss protein molecules called prions, which turn out to be remarkably similar to his hypothetical gemmules.

The magic happens when prions interact with the rest of the cell.

Prions are found inside cells and can take on different shapes, based on environmental conditions such as temperature or the presence of certain chemicals. Once altered, these proteins can bump into other prions and cause them to take on the new shape as well. When the cell divides, both daughter cells will contain prions of both states, and the chain reaction can keep occurring in that new generation.

The magic happens when prions interact with the rest of the cell, and even with DNA itself. The different shapes can cause different proteins to be made, or different parts of the DNA to be read or ignored, which can then trigger different actions or developments in the cell or the whole organism. If the external conditions change though, the other form of the prion will take precedence, and once again perform the original function.

Some may actually become incorporated into the DNA.

Halfmann and Lindquist even state that “these traits can ultimately become hardwired by subsequent genetic changes,” meaning some prion alterations may actually become incorporated into the DNA, thus blurring the line between genetics and epigenetics and raising intriguing chicken-and-egg type questions.

Whale-Size Implications

The broader implication of prions on epigenetic inheritance and evolution in general is that the ability to form different structures or perform different functions can be selected for at one time, and then kept around though unexpressed for generations, just waiting for the appropriate environmental trigger to reappear. When it is next expressed, other changes to the species may cause the original effect to take on slightly new forms, thus the organism responds to the environment with an existing toolkit, but continues to take on new appearances.

As a purely hypothetical example, the appearance of webbed fin-like appendages in birds or mammals in aquatic environments could thus be a result of the ancient fish-fin programming being kicked into a new usage as a result of a return to an ancestral environment.

whale-evolution-char.jpg

Evidence of epigenetic adaptation and inheritance opens up many new doors of speculation about evolution. In early whales for example, could the particular effects of limb use for paddling, or simply living in a more buoyant environment have had epigenetic influences on the cells of adults or developing offspring? (NGS stock illustration)

Time for a More Modern Synthesis?

The overriding significance of these discoveries is that we now see concrete illustrations of how living things actively adapt to their environment even at a cellular level and can in at least some cases pass on those adaptations to their offspring. While theorized by many in the past, this is fairly new ground for modern discussions of evolution.

Prevailing view now clearly too narrow

The prevailing view that variation in a species is simply the result of a DNA program locked off from the world and altered only through random errors in transcription is now clearly too narrow. The study of epigenetics shows us that life and evolution are dynamic processes, based on the complex back-and-forth relationships between organisms and their entire environment.

And a Hint of Mind-Blowing Context

Finally, while these experiments and observations have been made mostly with single-celled organisms like yeast, or simpler animals like fruit flies, it’s important to remember that even the most advanced organisms are still made up of individual cells. Most remarkably, you yourself started out life as a single-celled organism, developing in an environment rich in chemical inputs and signals being produced by your mother in ever-changing response to her environment.

Andrew-Howley.jpgAndrew Howley is a senior producer for National Geographic Digital Media, responsible for editing the National Geographic website home page and the front page of National Geographic Daily News. He also manages the National Geographic Facebook page, which has more than 1,700,000 followers. Prior to joining National Geographic, Andrew was a programming manager at America Online, which included writing promotions for the Welcome Screen. He received a BA in Anthropology (focus on Archaeology) from the College of William & Mary, Virginia. His personal interests are history reading, painting, running, and developing educational projects.

Blog posts by Andrew Howley

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Comments

  1. Rick Viduka
    Palmdale
    January 14, 9:49 am

    The evolution hype in these articles never ceases to amaze me! Clearly microbiology has shown us it is time for a new theory. Darwinism is dead.

  2. Richard rvhalejr
    San Ramon, Calif.
    July 30, 2011, 8:16 pm

    So lets recap what I’ve just read:
    Genomics is in junior High school
    Proteomics is in Elementary school
    Epigenomics is in diapers

    There was more substance on Proteomics (Prions) than Epigenomics.
    However its Not this fine young gentleman’s fault.

    For a long time anyone that asserted the Proteomics was almost as
    important as Genomics was summarily dismissed without regard to
    the science backing the assertion.

    WOW, look at all of those citations from scientists standing up and
    saying, how did you put it, the “Prevailing view now clearly too narrow”.
    The silence is deafening.

    “And a Hint of Mind-Blowing Context” Son, I love your work but one of
    the major problems in Molecular Biology is that curing Cancer in Rats
    and Plants does not translate well to human beings. Author’s of Journal
    papers are notorious about using Human in the title, then you get
    down to the last word in the abstract and that will be (SURPRISE!) Rat.

    They will do anything to get that paper in as it is still publish or perish.
    Sometimes you have to track down the original paper (in the olden days
    that was called fact finding) and then find out it was a mold or mouse
    study. If any paper’s results or author’s assertion has not been reproduced
    on a human cell (even the researchers) then the probably of failure is at
    least 90% (p < .05)

    It gets worse, lots worse. The quality of many studies or trails is poor as
    all variables have not been identified and isolated (except for the one under
    investigation). This is an overly simplified example but goes a long ways
    explaining why so many papers have conflicting conclusions.

    So with our understanding of Proteomics being far from sufficient Epigenomics
    has been thrown into the mix. Epigenomics depends on methylation and histone
    patterns and those will change with every new phase and function of a cell, from
    being fully differentiated to how it should respond to typical stressors like nutrition
    or exercise until such time it should no longer divide do to old age and the likely
    hood that its Genomics, Proteomics or Epigenetic mechanism contains a mutation
    that will accelerate cell division, become immortal (by defeating Apoptosis –
    programmed cell death) become a tumor, metastasize and terminate its hapless host.

    We need to understand and recreate each temporal state in any given cell be it healthy
    or cancerous. That needs to be done in parallel with meta-genomics but with the
    U.S. economy in a death spiral no significant investment in R&D will take place.

    I think I need to find a better way to spend my time.