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Evolution in Kansas II

(Continued from Evolution in Kansas.)

From my personal experience, most people "questioning" evolution have only the vaguest notion of what the "theory of evolution" actually entails, and most of the time add in things which are distinctly not part of evolution.

I am not a biologist, and this article doesn't pretend to be a full description or treatise on evolution. It is just an overview guide for those people (Kansas school board members and their creationist supporters) who can't seem to (or don't want to) wrap their heads around what the theory of evolution is.

So, what does the theory of evolution say?

Let's start with what it does not say:

1) It does not say how life began.

The theory of evolution doesn't specify how life began, period. It doesn't matter to the theory: it could have been random chemical reactions, meteorites, angels, aliens, magic fairies, or gods. Evolution doesn't care. It is, by definition, about the evolution (changes) of life that already exists.

2) It does not say there is no God.

The theory of evolution has no opinion on the existence of God, gods, goddesses, etc at all. Any number of gods (or ghosts or demons) could exist and it wouldn't change the theory of evolution one bit. (It does of course directly contradict a literal Genesis, but then again so does nearly every other branch of science.)

3) It does not say how the earth or the universe began.

Evolution is not dependent on the "Big Bang", "Little Bang", or any other size "Bang" you want (see above).

4) It does not say that higher plants and animals arise from lower.

The theory of evolution has no concept of "higher" or "lower", only more or less suited for a particular environment.

5) It does not say that an evolving organism is "on the way" to another form.

Many people think evolution deals with endpoints; that one kind of organism "sets out" to become another. They think that evolution means that everything between chimpanzees and humans was just something on the way to the "goal" of being human. This is not the case. Every creature is a endpoint, and evolution does not have goals.

6) It does not say that one kind of plant or animal can give birth to a completely different kind of plant or animal, like a fish turning into a lizard in a generation or two.

This is a common mis-expectation, sometimes mistakenly called "macroevolution". Evolution would not be "evolution" if such massive changes happened in a single or even several generations, it would be "revolution".

7) It does not say that evolution proceeds by pure chance.

Chance plays a part, but the process is decidedly not random.

Ok, so what does the theory of evolution actually say?

1) At the topmost level, evolution is a theory that says the percentage of individuals with a particular genetic trait changes over time. So if 1% of a population of bacteria have a particular gene (say for antibiotic resistance), two weeks later it might be 1.1%.

This fact has been observed many times and is only denied by those who should not be let out of the house without a tracking collar.

Of course, that is not the whole story.

2) Also under the "evolution umbrella" are the theories of why the changes occur. The most widely known and important one is called "natural selection". There are others (sexual selection, artificial selection, etc), and all are involved, but we'll keep it simple.

Stating it as simply as possible, natural selection is what happens when a genetic trait gives some advantage to some individuals in a population. Therefore, they reproduce more (possibly by dying less) than individuals without that trait. This means the individuals with that trait now make up a higher percentage of the population than before. So, evolution happens by replacing those individuals in populations without a trait for those with that trait.

Again, this fact has been observed many times, and many (thinking) creationists even agree this happens. They call it "adaption" or "microevolution".

So where's the problem? Well, there are some sticking points (for creationists anyway; they are not sticking points for the vast majority of biologists):

3) Part of the picture is where the different genetic traits used in natural selection come from. Some may be pre-existing natural variations in a population, or come about because of sexual reproduction, but genetic mutations are also a source of differences.

Many (but not all) creationists believe that mutations, by definition, are always harmful; that is, a mutation could never benefit the organism that carries a mutated gene. After all, many human diseases are caused by broken genes (and broken jeans for that matter), and most movie mutants are horrible monsters who exist in perpetual pain. In fact, many creationists call mutation-fueled natural selection the "hopeful monster" theory.

In truth though, most mutations are tiny changes that involve just one or two changes in a gene, and neither benefit nor harm the organism. These mutations happen all the time. Through the already-accepted natural selection process, the harmful mutations are filtered out (the organisms die outright or can't compete), the neutral ones are left alone (until later when they might turn out to be either harmful or beneficial under different circumstances), and the very few beneficial mutations get selected and spread through the rest of the population over generations.

The fact of beneficial mutations really can't be denied. Examples of mutations both beneficial and harmful have been well documented many times. (Some creationists do deny it though, and they either need a library card or an aluminum foil hat.) Many creationists even agree that beneficial mutations exist.

So where does this leave us? So far, we see that evolution as a process works, and has been observed working. We know that natural selection works on variations in a population of organisms to change the genetic makeup of the group over time. We know that the ultimate source of the variations is genetic mutation.

Well, it seems like we have everything all wrapped up: Evolution exists, works, and has been observed… except that there are one or two more things:

4) Evolution also says that over time, very large differences can come into existence.

This is "macroevolution", or "big" changes. One common problem is that people often misinterpret the "macro" part and think it means "big changes all at once", but all the known evolutionary mechanisms act very slowly and over long periods of time, so "macroevolution" actaully means "big changes eventually".

Still, some creationists who do understand this distiction don't think it can work.

It seems strange for someone to accept all of the above points and then call this one preposterous. If you accept that changes in populations can occur over time, and than new changes can be introduced through mutations, and the changes can be acted on by natural selection, why would this one be so difficult to imagine? You just need to take tiny changes and add them over a very long time. Intuitively, it makes sense. You would need a process or barrier in place to prevent large differences from building up over time.

There is also a large body of evidence for macroevolution, but much of it is tied directly with the next point, so we defer the discussion for the very last component:

5) The diversity of life we see today is the result of changes in common ancestors in the past; changes which were brought about through the processes described above.

This is the "theory of common descent". It says that the theories of evolution and natural selection we talked about above can account for all the different kinds of organisms alive today, and that all species of critter evolved from a common ancestor species.

This is the biggest point of contention (with creationists), and is obviously denied by all creationists, by definition (if you don't deny this one, you are not a creationist, sorry). For modern biology, common descent is so accepted it is regarded as a fact, much like relativity, atomic theory, and the sun-centered solar system are facts in physics.

For creationists though, this one doesn't hold water. They feel it just won't work, or just can't explain why we have both dogs and carrots, plants and animals, or boxers and briefs. Some have somewhat plausible-sounding pseudoscientific arguments, some just deny the whole thing and point to the Bible as a reason.

Why this one is so difficult is beyond me. As I said, you would need something to actively prevent tiny changes from accumulating to the point you end up with very different organisms.

But luckily there is also a huge amount of evidence that macroevolution and common descent are true. This isn't complete list, just an overview:

- There are several extremely fine-grained changes shown in fossils. - There are many fossils which fit very nicely between different species (the so-called "transitional" fossils). - There are many more fossils which mark out the relationship of the different kinds of species. - The fossil record is sorted from oldest to newest, with earlier organisms in older rocks than newer ones. - There are animals with parts they don't need (i.e. whales with tiny leg bones). - There are many different species of animals with identical and very similar chunks of DNA. - The DNA evidence matches up with the fossil and taxonomic evidence: plants and animals that fossil evidence says should be closely related are also closely related via DNA. - There are many living species all just slightly different from each other, and can be seen moving further apart over time (called "radiative adaptation"). - There are the many human-selected changes in pet and agricultural species: dogs, cows, other pets and farm animals, and most impressively, agricultural plants like the cabbage family. (While they may not necessarily be distinct species, it shows that huge changes are possible by simple variation and selection.) - There are observed instances when new species arise (not discovered, arise).

For a huge amount of further reading, please see 29+ Evidences for Macroevolution.

Of course, a creationist can just say "None of this is evidence, God just created all those things as they are." Nobody can argue against that. Presumably God wants to fool us into thinking evolution happens.

One final thought:

why should this author take the time to write this article? First, evolution is a fascinating subject in and of itself. I am interested in all of science, and biology and evolution are especialy "neat". Second, evolution is fundamental to understanding biology, health, and humanity itself, and so should be understood by everyone. Finally, there are people who do not understand evolution, but for some reason feel this lack of understanding is no barrier to making decisions on what should be taught about it in schools.

I don't believe this last group will read this, but writing this made me feel better.

See also:

2005-09-09

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