Monday, August 5, 2013

What Is Evolution, Is It True, And Why Do We Care?

Where to begin?  Evolution is the ‘guiding principle’ of biology.  As a subset of biology, evolutionary thinking can help us understand diet/nutrition.  So I will begin with evolution, but I won’t end there.

What is Evolution?

I would like to assume that everyone (with access to the internet and other first world sources of education) would have a basic understanding of what evolution is, but after listening to some of the questions directed to Richard Dawkins it’s clear that many people don’t have a clue. 

For longer and more detailed explanations see the Wikipedia articles on Introduction to Evolution and Evolution, or you can read a biology textbook, etc.  For a quick explanation of evolution see either one of these two videos

What evolution is not: 

  • Evolution doesn’t explain how life on earth began, abiogenesis does
  • Evolution doesn’t explain how the universe began, the Big Bang does (maybe it doesn’t, but this blog isn’t about theoretical physics)
  • Evolution is not random.  There are random mutations, random gene recombinations and a random allele in gametes (eggs and sperm), but there is non-random selection (natural selection*)
  • Humans didn’t descend from chimpanzees.  Humans and chimpanzees shared a common ancestor several million years ago
  • Evolution (in the real world) isn’t like Pokemon evolution (where a chimp could turn into a human).  “Evolution is the change in the inherited characteristics of biological populations over successive generations” 

* Also referred to as ‘survival of the fittest’ where fitness is reproductive fitness rather than athleticism (though in the natural world the two are often related). 

Is It True? 

Yes.  Rather than bombard you with arguments I would rather take one logical, common sense approach. 

  • Do you agree there are traits organisms possess that are hereditary (such as height, eye colour, hair colour, etc) and that there is variation in a population with regards to these traits?
  • Do you agree that selection pressures in the environment can select for desirable traits (such as people with lactase persistence in agrarian societies having access to more food sources, therefore increasing their chance of survival and reproduction)?
  • Do you therefore agree that the next generation of this species would have more of the desired trait than the previous (the next generation of people having a higher proportion of lactase persistence than the previous generation)?  If you have you have just agreed with evolution 

Evolution simply follows from there being: 1) variation in a population due to heritable traits and 2) certain heritable traits being more successful than others.  If you agree with (1) and (2) you agree with evolution.  No divine intervention necessary 

You can see evolution in the world, for example: 

Antibiotic resistance and related: A small number of bacteria (bacteria X) in a given species have mutations that allow them to survive antibiotic Y.  Upon exposure to antibiotic Y all the bacteria die except for bacteria X, which then multiplies rapidly without much competition from other bacteria and become very successful.  As a larger part of the bacterial population is now comprised of bacteria X the overall bacterial population has become more antibiotic resistant. 

Rapid changes apply to all organisms under strong selection pressures (even including some populations of elephants who are increasingly become more tusk-less as a result of poaching), but particularly in organisms that reproduce rapidly.  A similar kind of 'resistance' can also apply to tumour cells in cancer, see Genes and Cancer 

Breeders: Animal and plant breeders select desirable traits in their own little population and only allow those animals/plants to reproduce.  Consequently the population of offspring have a higher proportion of those desirable traits than the previous generation (whether its making a shorter dog, the spontaneously hypertensive rat or a chicken that lays lots eggs). 

If the knowledge of evolution was somehow magically erased from our minds then biologists and clever breeders would simply rediscover it again because they will see the patterns, and understanding those patterns is so important for their area of work. 

Why Do We Care?

Evolution helps us understand biology.  One way in which it does so, that's quite relevant to the blog, is mismatch theory.

Just as evolution follows from there being 1) variation in a population due to heritable traits and 2) certain heritable traits are more successful than others, so too does mismatch theory (or genetic/evolutionary concordance/discordance) follow from evolution.

Mismatch theory essentially suggests that due to selective pressures species are more adapted to certain environments and less adapted to others.  And that problems may occur when species are placed in environments that they are poorly adapted to.  Again, common sense.  I'll continue with mismatch theory next week.

* I'm not religious and I don't mind whether you are or not, that's not the point.  Evolution is a useful tool for asking questions and improving our understanding on matters related to biology.  I simply want to draw attention to its usefulness and clear up any misconceptions.

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