Theory of Evolution- the case for it


So, the theory of evolution is a huge controversy in the US.  I haven’t waded into the fray on this topic much, I didn’t know enough to really make much of a statement.  Having started a Genetics and Evolution course on Coursera, and having been reading through Jerry Coyne’s book  Why Evolution is True, I feel I can help to offer a modest defense.

First, a few bits of definition.  Proper understanding of a scientific theory depends on a proper understanding of the terminology, as used in the relevant scientific community.

Theory- A theory is an explanation for observations that has stood up to repeated tests and further observations.  Predictions made based on the theory turn out to be true, and independent researchers can get the same results as the original researcher.  The everyday use of the word “theory” is closer to a scientific hypothesis, which is a proposed explanation for an observation which has yet to undergo rigorous examination.  A theory is as close to a true fact as you can get in any discipline other than pure mathematics.  ”Just a theory” as an objection to evolution makes as much sense as “it’s just a theory that you need to breathe air to live”.

Evolution- The change in species over successive generations.  Note that this is a change, it does not explain, nor does it attempt to explain, where the first species came from.  That’s abiogenesis, and while there are some proposed explanations, scientists are still far from a conclusive answer.

Natural Selection- The tendency for certain variants of a species to reproduce more successfully than others.  This is the main driving force in evolution, though there are others.

Now, to avoid this post getting too long and straying too far into “I don’t know as much as I think I do” territory, I will stick to a very small part of the case for evolution.  More will come in later posts, but here’s the first part- Evolution by natural selection is inevitable, given sufficient time, and 3 criteria which I’ll make a case for here.  The “sufficient time” issue will be covered in a later post.

The three criteria are:

1) Individuals in a species must vary from one another

2) At least some of these variations must influence the reproductive success of the individuals that have them.

3) At least some of the variations in (2) must be inheritable, from parent to child.

You should see why it would be inevitable.  If people vary in ways that can influence reproductive success, some people in that population, specifically those with variations increasing reproductive success, will have more kids.  These kids will inherit the ability to have more kids.  Over time, whatever it is that lets this lineage have more kids will come to dominate.

Are these criteria met?  I hope you aren’t seriously asking that.  Just look at the peppered moth.  They have various coloration patterns on their wings.  Centuries ago, white was common, black much less so.  Point 1 proven.  The Industrial Revolution hit, which darkened trees and killed lichen that matched their whitish coloration.  The black ones were able to survive to childbearing age more reliably, point 2 proven.  In a few decades, the black variant became vastly more common than the white.  Clearly inheritable, point 3 proven.

Of course, whether there has been sufficient time for this to produce the full biodiversity we see on earth is another matter.  The process being solid doesn’t mean much if there hasn’t been enough time for it to do its thing.  The short answer- yes there has been enough time.  The long answer, I think I’ll get to that later this week or perhaps early next week.

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