1.  What is Evolution?

There’s a very accurate, but also somewhat snarky definition of evolution floating around the internet – here, for example: http://i.imgur.com/2byyo.jpg.  The problem is that as accurate as it is, it isn’t particularly useful or engaging.  It’s liable to make a small group of people chortle smugly and most everyone else click away.  We’ll have to run on a bit longer than the 12 points in the image, but let’s try to talk about this a little more personally and answer the question “What is Evolution?”

Evolution is an idea that says creatures change.  From generation to generation the change may be small, but over tens or hundreds of generations the changes can be as significant as branching into a new species.

(It’s important to note here that the concept of a “species” is a difficult one, because it’s attempting to apply our concepts of categorization on a reality that can be fuzzy around the edges.  Within species that reproduce sexually (like us!), a handy rule of thumb is that if the creatures can interbreed successfully and regularly produce fertile offspring of both sexes, then they are members of the same species.  In creatures that don’t reproduce sexually – especially micro-oganisms – the defining lines between species becomes much more difficult to draw.  More here, if you’re interested: http://en.wikipedia.org/wiki/Species#Definitions_of_species )

The idea of evolution says that over generations, creatures adapt to fill roles or niches in the environment, or are weeded out as those niches are eliminated.  Let’s consider as an example a flock of birds that crosses a mountain range one particularly good summer, migrating to a new environment mostly similar to their old.  However, in addition to their regular food supply of berries and grubs, in this environment the birds encounter a seed that is very nutritious, but also comes in a thick shell.  Within this flock of birds there is some variety – among other differences, some of those birds have stronger beaks and some have weaker beaks.  The birds with the weaker beaks aren’t able to crack the shells of these new seeds, so they rely on their berries and grubs, while the birds are able to enjoy all three – seeds, grubs, and berries.  The birds with the stronger beaks have a better, more stable, more nutritious food supply, so in general they will be healthier, and in general they will have more eggs which hatch with a better chance of survival.  Because a strong beak is a genetic factor, their hatchlings are more likely to also have strong beaks.  Eventually over a number of generations, the birds with the stronger beaks are likely to outnumber (and potentially completely replace) the birds with the weaker beaks.

Let’s say, too, that this same flock of birds has some rather bright-colored feathers.  In their previous environment they had few predators, and brighter feathers were a sign of health, so the she-birds were most interested in the he-birds with the bright feathers.  But on this side of the mountains there are hawks with excellent color vision, and the birds with the brightest feathers are the most likely to be eaten (and thus the least likely to have a large, healthy brood of chicks).  Even if the she-birds still prefer the brighter birds, the predation of the hawks will drive down the population of the brightest birds while the birds with duller feathers will thrive.  (Eventually it’s likely that the she-birds who are interested in duller birds will be more common, since those who prefer bright he-birds are more likely to have their children eaten by hawks, so they won’t successfully pass on their genes.)

It can be said that the environment has “selected” for birds with stronger beaks and duller feathers, in the similar way that a dog breeder might select for longer coats or shorter legs over several generations.  There is no intent in natural selection of course, only the statistical likelihood that the creatures most suited for an environment are the ones who will have the best chance for survival.

Where do these changes come from?  Why might one bird from the same brood have a stronger beak, and another have duller feathers?  The answer is DNA.  In sexually reproducing creatures, each conception is a toss of the dice: 50% of the mother’s DNA selected at “random”, and 50% of the father’s, are combined together.   Most of us studied meiosis in school, so it’s enough to link to refresher here: http://en.wikipedia.org/wiki/Meiosis .  In general, two unrelated humans share about 99.9% of their 3 billion base pairs, and the remaining 3 million base pairs are organized into about 10,000 or so genes.  If those two unrelated people have completely different genes (this is unlikely), there are about 10 thousand squared, or 100 million possible combinations of genes their offspring can have.  If there are an average of 4 different types for each gene (there are more), one could say that there are 10 thousand to the fourth, or 10 quadrillion different possible combinations of human DNA.  This doesn’t account for point mutation, which is as common as cancer.  Minor disruptions to our DNA – errors in copying, extra copy and pasting, damage caused by free radicals and radiation or foreign substances (e.g. Thalidomide babies) can alter the gametes (sperm and eggs) which will join to become the next generation.  In most cases, genetic damage is either too minor to have any advantage or disadvantage, or the damage is severe enough to render the creature infertile or unlikely to reproduce.  Occasionally, the result is more striking, but nominal (see, for example, the introduction of blue eyes to humanity: http://en.wikipedia.org/wiki/Eye_color#Blue), and even more rarely it is helpful (like the ability to digest lactose as adults: http://en.wikipedia.org/wiki/Lactose_intolerance#History_of_genetic_prevalence).

You may say at this point that you accept that these differences are enough to form new races (among people) or breeds (among dogs), but not enough to form new species.  You’ll require more evidence, and that’s understandable – it’s coming in future installments.  For now, just understand two things: 1) If two groups of the same species are continuously able to interbreed, they are unlikely to speciate.  If our birds described above were able to fly back and forth across the mountains to mingle with the other flocks, they would not be likely to form a new species.  Humans have been a relatively mobile creature for quite a long time, but before that was the case there is evidence that they did speciate, and there were multiple groups of different species of humans existing simultaneously in different environments (http://en.wikipedia.org/wiki/File:Humanevolutionchart.jpg).

What’s important to understand, though, is that the idea of evolution does not suggest you are likely to see a new species form inside of a stable population.  If our birds speciated as they grew stronger beaks and duller feathers, it would not be because of an “Adam and Eve” bird couple that appeared by happenstance among the flock and their children’s incestuous relationships.  The environment would drive the entire flock to the new species over many generations as the weaker-beaked birds died faster in harsh winters and the hawks ate the brightly-colored hatchlings.  It would only be by comparison to the flocks across the mountains that you would see a substantial difference.

Evolution is a theory, just as gravity is a theory, as elementary chemistry and electromagnetism are theories, and as string theory is a theory.  A “theory” in scientific parlance may be a fact in regular conversation, or it may be a wild speculation.  A “theory” is only a model for explaining things, and it can be backed by centuries of data and research, or it can be wholly unsubstantiated.  Science refers to even “proven” models as theories instead of facts, though, because the models are in a constant state of revision as new data is received.  In many theories, this revision is minor and around the edges – we understand the core of elementary chemistry and electromagnetism very well, and rely upon that understanding in our day to day life.  Research there generally expands the periphery of our understanding; we don’t expect to see those theories completely overturned soon, or really ever.  Our understanding of gravity is much more uneven – we know pretty well how it works, but understand very little of why it works, and the theory of gravity in that regard seems to change dramatically every few decades.  The theory of evolution, as scientific models go, is considered to be extremely robust and well-supported.  At this point, less work is being done to substantiate evolution because the “how” and “why” of it are so well understood.  Much more work is being done to fill in the gaps of history – to join the fossil record between the branches and the twigs on the tree of life – and to find new ways to apply evolutionary theory in a useful way, like producing a species of micro-organisms that eats garbage and excretes fuel.

Evolution is NOT an explanation for the origin of the universe or even life.  Evolution has nothing to say about the Big Bang – that is another field of science entirely: cosmology.  Whether or not the Big Bang Theory is the best model for the beginning of the universe does not affect the theory of evolution.  Similarly, whether life originated in a lightning-struck pool of murky water on primordial earth, or was carried in by comets from other worlds, or was deliberately placed on earth by ancient astronauts or God or gods does not affect the theory of evolution.  Evolution only says that life will adapt to its environment because of natural selection; it does not include a model for genesis.  Many people with a particular view on evolution also have particular view on how life began, but it is also true that they tend to have a particular view on the ultimate future of life (and especially human life) on earth – another topic on which the theory of evolution has nothing to say.

Evolution is NOT a philosophy.  The Catholic Church officially espouses evolution.  There is no official overarching Buddhist stance on evolution, but generally Buddhist thought considers it compatible, or irrelevant.  There is a trend to speak of Darwinism as a school of philosophy rather than a collection of scientific theories (its original, and useful meaning), conflating it with elements of philosophical naturalism, utilitarianism, and Spencerism, and thereby to tie it into Nazi ideology and breeding programs (which are in fact the opposite of natural selection and more akin to husbandry).  One can be a theist or an atheist and subscribe to the theory of evolution.  One can accept evolution and be a communist (though communism, like the nazi breeding program, is actually an example of unnatural selection) or a staunch capitalist (it is easy to argue that the “market” practices a model of natural selection).  One can be selfish or altruistic and find evolutionary support for their stance.  Evolution has nothing to to say, either positively or negatively, about morals or any particular morality beside offering a model that might explain the origin of those morals.

So, now that we understand what evolution is, we can move on to looking at the evidence for and against it to see if it’s an accurate model.

I hope to continue to post at least once a week.  Future topics are likely to be

2. What Proof Exists?
3. Intermediate Fossils
4. Why Are There Still Monkeys?
5. Can We Prove Evolution If We Can’t Observe It?
6. Why Not Intelligent Design?

But if you have questions you think need to be answered, let me know!  I’ll be happy to change those plans if there’s some aspect of evolutionary theory you think is particularly weak that I don’t plan to cover.

Please comment!  Let me know if I’ve made any mistakes or overlooked important points.  I invite both conversation and debate, and understand the difference between the two.