The Clever Badger To add insult to injury, the platypus is leading.

A Short Evolution Refresher

Geeks are Sexy has a nice post from a bit over a year ago giving a solid, high-level overview of evolution.  It also includes an excellent 10 minute video that I'm including below, because it deserves as wide an audience as possible (I may have posted this before.  If I haven't, I should have).

The article and video hit a number of frequent objections to evolution.  Actually, it would be more correct to say that the article and video address a number of objections to a strawman caricature of evolution.

The distinction is important because more often than not, the vocal evolution deniers out there will start their sales pitch by claiming that "evolution says <something>", and typically that <something> is either something that evolution doesn't "say" at all, or else "says" quite a bit differently than the denier suggests.  Some examples:

• Have you ever seen a dog give birth to a cat?
• Evolution says that man came from monkeys, so why are there still monkeys?
• DNA evidence proves that all humans came from one woman!
• Most mutations are harmful and would kill an organism!

The first two, of course, are the same concept phrased slightly differently, and reflect at least three misunderstandings - that individual organisms evolve directly into other individual organisms like some sort of Pokémon,  that one species will cease to exist once it gives rise to a new species, and that humans are descended from monkeys.  (There's a part in the video starting at 5:33 that covers these with a nice little graphic.)

The third one is a distortion of the concept of the Most Recent Common Ancestor (MRCA). We commonly see the term applied to the unfortunately named idea of a Mitochondrial Eve - the most recent common female ancestor of all living humans.¹

The reason that it's a distortion is that the MRCA depends on what group you're looking at.  The MRCA of all living humans is not required to be the MRCA of all humans that have ever lived:

(From Wikipedia)

The MRCA of everyone alive today could thus have co-existed with a large human population, most of whom either have no living descendants today or else are ancestors of a subset of people alive today. The existence of an MRCA does therefore not imply the existence of a population bottleneck or first couple.

At this point, some alert individual might assert that even if you expand the pool to all humans that have ever lived, you still necessarily end up back at a first couple, but you'd be wrong because there isn't a requirement that the female MRCA and the male MRCA live at the same time.  Think about it.  If our notional female MRCA had children by two different men, and descendants of all of those children survived to the present day, then neither of her partners would be the male MRCA - her father would be.  (There's also the little matter of identifying exactly where you draw the line between human and non-human.  For a very relevant graphical demonstration, see here.)

The last point is simply untrue.  Most mutations aren't fatal.  Most are neutral.  The fatal ones tend to get removed from the population pretty quickly for obvious reasons.  Neutral ones can just sort of drift around in the gene pool without any particular consequences.  Beneficial ones tend to increase in frequency.²

We could go on with this, and we'd see the same thing over and over again.  That suggests to me that the evolution deniers out there aren't at all interested in addressing the subject on the basis of facts and evidence, but rather seek to turn it into an exercise in emotional manipulation.³

The lesson here, as always, is to do some fact checking when you run across references to cats birthing dogs and such.  If nothing else, ask yourself  "if this is such a simple and obvious flaw in evolution, then why on Earth does anyone still accept it?"   Your answer should be "maybe this supposed flaw has already been addressed, or maybe whoever proposed it doesn't understand evolution very well."

-Jay

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¹So named because mitochondria within cells come from the mother - sperm lack mitochondria. Similarly, we can talk about a Y-chromosomal Adam.

²But remember that beneficial depends on the environment, and may be a tradeoff.  Conspicuous physical displays may increase the chances of finding a mate, but may also increase the chances of getting eaten.

³Ken Ham is perhaps the current master of this approach. What the man actually knows about evolution is unlikely to fill a thimble, so he takes the fear-mongering approach of linking evolution to everything that is bad in the world. Ham also attracts attention for his horribly distorted theology. James McGrath recently had a post up summarizing some of the criticism Ham has been receiving from within the evangelical community of late.