I was recently challenged to summarize the "best evidence for macro-evolution" that I could find in 1200-1500 words. However, as it is impossible to comprehensively
discuss evolutionary theory in so few words, I will simply touch on some of the universals --- common misconceptions, objections and arguments, incorporated into what I hope will be seen as a sort of basic overview. In fact, as many of the objections I encounter tend to be based on a misunderstanding of some aspect of evolutionary theory, I'm hoping that simply explaining
it properly will help dispel many of the myths about evolution and objections to evolution.
Before I get started, let's discuss what evolutionary theory is not
; evolutionary theory is not
a statement of "morality." Evolution is a statement of what we believe happens. It says nothing about whether what happened was "good" or "bad" or "prescriptive." It is simply a descriptive theory of the development of life on earth. There is no real or necessary moral component to evolution, so this essay will not be addressing moral objections to evolutionary theory. Evolutionary theory says that evolution happens whether we want it to or not.
Also, evolution is not concerned with "random chance" as a driving force. In fact, natural selection, the primary driving component of evolution, is the exact opposite
of random chance: it is the principle by which nature favors that which helps something survive, and rejects that which makes survival more difficult. Nothing "random" about it.
Now, let's start with one of the most common objections: How did the first life arise, according to evolution?
This is a simple question; evolution does not have (nor does is require) an answer here. Evolutionary theory can be tested whether life was created by an "intelligent designer" or whether it arose naturally. So I will not go into much detail here, except to say that any life which was formed naturally would have to be simple by definition, thanks to the law of probability (simplicity begets simplicity --- if the first life were complex, it would require an origin as complex as itself, probably moreso, conditions which are exceedingly improbable). However, even if the first life was some kind of miracle that had been zapped into existence rather suddenly, then evolution could still be tested; the only predictions evolution makes about the origin of life are: (1) it was simple; and (2) that it was the ancestor of every creature that exists on earth today.
How do we know (2) is true, you might ask? We can observe that all life on earth is related from one simple fact, which we will discuss more in a moment: we are all made of DNA.
DNA is the basic building block for life as we understand it. There has been no discovery of any other life on earth (or anywhere else) that is not
built on DNA. Even bacteria and viruses have DNA. The simplest and the most complex organisms have DNA. If we ever do discover a form of life which does not
have DNA as its foundation, then we will have a counterexample to the claim that all life on earth is related; according to most naturalistic abiogenesis theories, the origin of life probably only happened once, or during a very short "window" of time --- pit that against the long, long time it would take for evolution through natural selection to produce varation and speciation, and you will see that it was not likely that very many sources of life sprang into being naturally, at separate times. In fact, a naturalistic origin of life almost requires
a startling degree of improbability; if a naturalistic origin to life were very probable
, we would be seeing a lot more of it, wouldn't we? So it's safe to hypothesize that there was probably just one (or very few) "original ancestor(s)." If the generation of life from nonliving matter is indeed that
improbable, then this ancestor(s) would (naturally) have to be the origin of all other
replicating life on earth. This self-replicating organism would eventually give rise to the first "population," or group of organisms of the same species.
All that is required for natural selection, the foundational aspect of evolution, to take effect is a self-replicating
(or "reproducing") population, such as the one described above. Once we have a self-replicating population, we have "competition" for resources --- against nature, even against other organisms (organisms sometimes compete even against their own genetic relations or family, without even realizing it, such as siblings who have to share food). With such a simple organism as the first natural life, this competition would of course be very simple, almost poetic --- the organism might not even be aware that it is competing --- but by the simple fact of its existence (and its continued efforts, guided by natural, unthinking chemical processes), it "competes," with nature and with others of its kind (whether or not it "means" to), for the resources which drive these processes.
At this point, some people raise the objection, "how does a simple life-form become more complex?" They have a particularly odd way of phrasing it, by asking, "how can new information enter the genome?"
The best way to answer is through example: take hemoglobin in human blood. All of our globin genes are related to each other (that is, moreso than to any other gene in the body). They appear to have "speciated" from a single "parent" globin gene at some point, within our great great great (times a thousand) ancestor. At some point, that globin gene duplicated, perhaps because of a mutation, and made "copies" of itself. Over time, these benign genes mutated separately on their own, until they adapted to each other's presence within the same chromosomes, isolating into two "clusters," the alpha and beta clusters. This splintering process continued again to give us the zeta cluster and the alphas used in adult humans. Further, this mutation happened far back enough along our descent that it is visible in many nonhuman
species --- species which were descended from the same common ancestor as humans, the ancestor in whom these mutations took place! That is certainly an odd phenomenon --- or it would be, if we did not have evolution to explain the connection.
So the simple answer to the information question is: one gene suffers a benign mutation, creating a copy of itself. Later, that copy mutates further, but in a different way than the original, creating "new" information.
And now, moving on, we come to the crux of the matter: speciation. This essay was written with the assumption that you accept what is called "micro-evolution," so I won't go into detail about that or about artificial selection (dog breeding is a great example of both "micro-evolution" as well as artificial selection), but rather, I'd like to discuss what is normally seen as the logical result of "micro-evolution," called "macro-evolution." Whereas micro
-evolution consists mostly of mutation and genetic drift, both of which can be demonstrated easily in just a few generations of selective breeding (such as with dogs), macro
-evolution is what happens when this takes place over a much, much longer period of time --- as the title implies, "macro-"evolution is the stacking-up of large amounts of these traits with time, such that they displace the "norm" of a population (or even drive two or more populations apart). Many people have a hard time accepting "macro-evolution," but strangely, accept "micro-evolution." I've been asked to present the "evidence" for macro-evolution, but since I think this rejection of "macro-evolution" is due in part to a significant misunderstanding of what macro-evolution is
, I will first diverge and explain that a little bit.
Macro-evolution is otherwise referred to as "speciation" --- the "splintering" of a population into two or more sub-populations of different "species." The common misunderstanding comes from the use of the word "species" --- a "species" in the biological sense is not necessarily a completely different (or even radically
different) creature from its parent population; rather, there are a few basic criteria used to determine what sets apart different "species" in similar populations. Given my strict word limit, I'll only focus on one, the simplest --- the "Biological Species Concept," under which a "species" is defined simply as "being reproductively isolated from other species" (which simply means, "they cannot or do not interbreed"). Further muddling the situation is the definition of "reproductive isolation," which, in evolutionary theory, does not necessarily even have to be literal
reproductive isolation --- there are many cases of "speciated" birds which fit the technical definition of "reproductive isolation" from one another, and yet in theory are still capable of interbreeding.
This also happens with flowers; flowers tend to only reproduce with their own "species," although many are capable of (and sometimes take part in) reproduction with other species (this is called "cross-pollination" or "hybridization"). The fact that they can technically interbreed, though, does not make them the same species. So in order to truly appreciate what is meant by "speciation" in evolutionary theory, one must understand how a "species" is defined. Also important, though, is how speciation occurs.