I posted a slightly different version of this some time ago, but perhaps it’s worth revisiting the subject of biological evolution.
One of the more frustrating things about teaching biology is not that so many students are shockingly ignorant of biological evolution, which is the keystone of all modern biology – but how very many of them are shockingly
misinformed about it. Mere ignorance is okay; people are smart, and can learn. What’s harder to deal with is those who
think they know what evolutionary theory is all about, but have been horribly misinformed. It’s much harder to teach those who think they already know everything they need to know about the subject – especially when their “understanding” of the subject is exactly 180 degrees from reality.
On a frequent basis, I encounter students who’re shocked to learn that evolution is
not a theory which claims that the complexity and diversity of life is due to random chance. At times, you have to wonder how anyone could actually believe something so silly is true. Anyone who believes that evolutionary theory claims that the complexity and diversity of life is due merely to random chance must, perforce, believe that virtually every practicing scientist in the world is a complete idiot, and/or that virtually every one of them is an active participant in the most unimaginably vast (and pointless) conspiracy in history.
Such a belief is not just wrong, it’s
insulting.
Students frequently express surprise to learn that evolutionary theory does not claim that some monkey once gave birth to a human child, and that’s how
Homo sapiens came into existence. Such a thing, if it could occur, would be strong evidence
against modern evolutionary theory, actually. And it’s such a patently absurd suggestion that you really have to wonder who on Earth could actually
believe that evolutionary biology makes such stupid claims.
Students often say, during the first lecture, “But I’ve always heard that there’s no evidence
for evolution, and plenty of evidence
against it.” Really? Where is this contrary evidence? Somehow, the scientific community has managed to miss it. Strangely, whenever Creationists are asked to produce this evidence, they suddenly have other priorities. And as for biological evolution being unsupported by evidence, that’s an outright lie. It is – with the possible exception of quantum mechanics – the best-supported scientific theory in existence, as a trip to any decent college or university library can easily confirm.
Another very common “objection” to evolution is that “it’s only a theory.” This, of course, shows not just a complete lack of understanding of evolutionary theory, but a complete lack of understanding regarding what a theory
is. In the sciences, a theory is a well-tested and well-supported
explanation for some observed phenomenon. In fact, a “theory” is as good as it gets.
Actually, evolution is both a fact and a theory. It is a
fact that populations of organisms change over time – that change is
evolution. The
theory of evolution is an
explanation for that fact.
So, why are so very many people so completely misinformed as to what evolutionary theory is
actually about? Well, I think that one big reason is that there are a lot of people out there who, for whatever reasons, are actively
lying about evolutionary theory. They’re spreading falsehoods and claiming that evolutionary theory makes claims that no sane person could
possibly believe.
Many of them, no doubt, are simply repeating what they’ve been taught to believe about evolutionary theory – absurdities to which they’ve given little or no serious thought, apparently. That's sad, but not overtly dishonest. This is probably the biggest category of evolution-deniers – people who have been told by those they trust that evolution is false – and have made little or no effort to learn anything about the subject from other sources.
Others, no doubt, reject evolutionary theory because they believe it conflicts with their religious beliefs. One should never discount the human capacity to believe that what they
want to be true
is true. As such, someone who’s committed to the belief that evolutionary theory
must be false (because it’s a “Satanic lie” or some such thing) will latch onto every piece of evidence they think can somehow be interpreted as “disproving” evolutionary theory while simply refusing to admit that the (literal) mountains of evidence contrary to their position exist.
Such people are frustrating to deal with, but they aren’t necessarily deliberately dishonest.
The ones who are really frustrating are the deliberate liars. They’ve figured out that there’s a great deal of money to be made peddling their lies to people. Surely, at least some of the “Professional Creationists,” as I like to call them, must be perfectly aware that they’re lying, since they’ve been repeatedly corrected on their mistaken “facts” – only to continue repeating them. People like Duane Gish, William Dembski and their ilk have had their misrepresentations publicly corrected on many occasions – so they cannot possibly claim that they’re
unaware these claims are false. As such, it seems like a cynical willingness to say things they know to be false, rather than simple misunderstanding.
Of course, if your livelihood – indeed, your entire
worldview – depends on believing that basically every professional biologist (and geologist, and cosmologist, etc., etc.) on the planet is either a complete idiot and/or is an active participant in a massive (presumably Satanic) conspiracy to hide the truth, the capacity to suspend reason and ignore contrary evidence is simply astonishing. So, I’m not discounting the possibility that a lot of the “Professional Creationists” have managed to convince themselves that they drivel they spout is actually
true. But, surely, a lot of them must be perfectly well-aware that they’re lying.
So, while I don’t doubt for a moment that most Creationists (and I don’t regard the distinction between “Intelligent Design” and “Creationism” to be particularly significant, at least for the purposes of this essay) are honestly convinced that evolutionary theory is bogus (either because they’re simply ignorant, or because they’re incapable of believing otherwise), I have very little sympathy for the con artists out there who gain fame and fortune by deliberately deceiving the public on this matter.
I have no real problem with those who are merely ignorant or misinformed; it isn’t their fault. But that there are people out there who make their livings by deliberately lying about such subjects as evolutionary theory – for what purpose? power? money? – is just shameful.
I have no doubt that I could easily pen an “authoritative” tome that “proves” evolutionary biology is a sham, and that the only people who “believe in” it are a bunch of evil atheists out to undermine all that’s good and decent. I’d probably make a fortune. Goodness knows, there certainly appears to be a thriving market for that sort of drivel.
But I’d never be able to live with myself.
Personally, I find it both depressing and frightening that polls consistently show that approximately 50% of my fellow countrymen believe the Earth to be only a few thousand years old, and that the field of evolutionary biology is all a sham. There are lots of reasons for this shocking level of ignorance, of course, but one big reason, in my opinion, is that scientists and educators have done a poor job of educating the American public.
Far too often, educators find it easier to avoid the “controversy” over evolution, and so they fail to explain it to students. And if students don’t understand the relevant science, is it any wonder they’re such easy prey to the “Professional Creationists” – whether the “Young Earth Creationists” or their slightly more sophisticated brethren, the proponents of “Intelligent Design”?
And far too many in the scientific community simply cannot imagine that any intelligent person could actually believe that the Earth is only a few thousand years old, or that anyone could be so ignorant as to be unable to see through the flimsy “logic” of Intelligent Design “theory” – and so they write the anti-evolutionists off as a small “fringe” group. Far too many professional scientists, in my experience, simply cannot bring themselves to believe that there are significant numbers of people out there who don’t accept the fact of evolution, or that such people have any influence. It’s a deadly mistake, I think.
Even worse, many in the scientific community seem to believe that it’s somehow “beneath their dignity” to engage the general public and attempt to explain scientific matters. In this sense, far too many scientists act like they’re members of some sort of secular priesthood, as if it’s somehow beneath them to “waste” any time explaining to mere “laypersons” what scientists do, what they do (and don’t) know, and why it’s important.
So, I thought it’d be nice to consider the subject of biological evolution.
What is Biological Evolution?:
At its simplest and most basic, biological evolution is simply the fact that populations of organisms undergo genetic change over time.
A “population” is a group of organisms of the same species that lives in some defined geographic area. An “organism” is any living thing, whether plant, animal, fungus, bacterium, politician, or whatever.
It’s important to keep in mind that individual organisms do not evolve – evolution refers to changes in
populations,
not changes in individuals (that’s “development,” by the way). Ultimately, evolution refers to changes over time in the genetic makeup of populations.
Stars, planets, and even the Universe itself are often said to “evolve,” but this is not in any way the same thing as biological evolution. Cosmic “evolution,” while certainly relevant to biological evolution (presumably, there would be no living things if the Universe didn’t exist), is
not a part of evolutionary theory. This is because biological evolution requires heritable traits, which stars and planets do not have.
“Heritable traits” means those features that can be passed down from parent to child. Eye color, hair color, etc. are all part of the heritable makeup. Anything that an organism
inherited from one or both of its parents, and that it might
pass on to its offspring, is a
heritable trait.
In biology, the word “evolution” also often refers to
universal common descent. Universal common descent is the idea that all known terrestrial life is related, and descends from a single ancestral form.
Evolution as Fact and Theory:
When discussing the subject of biological evolution, we must distinguish between the
fact of evolution and the
theory of evolution. (Actually, there’s more than one theory of evolution.)
“Evolution,” as mentioned above, refers to genetic changes in populations of living organisms over time. That this occurs is not in debate. Therefore, evolution is a
fact.
“Evolution”
also refers to the universal common descent of living organisms – that is, it is regarded by the scientific community as proved beyond any reasonable doubt that all known terrestrial organisms are descended from the same common ancestry. Life may well have arisen several times in the Earth’s history, but all currently-existing terrestrial life uses the same 20 amino acids and shares the same genetic coding, meaning that we surely evolved from the same ancient ancestors. So, if you pick any two currently-existing species and trace their ancestry back far enough, you’ll eventually find a species from which they’re both descended.
The most recent common ancestor of any two species may have lived relatively recently (if, for example, you’re considering chimpanzees and humans), or it may have lived a very long time ago indeed (if, for example, you’re considering oak trees and humans) – but if you could trace the ancestry of any two species back far enough, and you’d eventually find a species from which both of them were descended.
Universal common descent is so thoroughly-supported through the fields of molecular biology, genetics, comparative anatomy, paleontology, comparative behavior, etc. that it is considered to be an undisputed fact within the biological community. Any one of these fields could easily have disproved common descent, yet every one of them provides overwhelming and
mutually consistent evidence for universal common descent. So, within the biological community, common descent is considered to be a
fact that has been demonstrated beyond any reasonable doubt.
The
theory of evolution deals with the various mechanisms which
cause evolution. Chief among these mechanisms are
natural selection and
genetic drift. Other mechanisms, such as autopolyploidy play an important but less-common role.
In other words, evolutionary theory is how we interpret the fact that living organisms evolve, and that they have been doing so for quite some time.
Modern Evolutionary Theory in a Nutshell:
Charles Darwin was hardly the first person to notice that populations of organisms change over time, nor was he the first to propose a theory explaining why this is true. He and Alfred Russell Wallace are remembered today because their observations and conclusions led them to formulate the theoretical elements that today form the core of modern evolutionary theory. Certainly, details of the theory have changed over time as new discoveries have been made, but the core of the theory remains unchanged even today. The core of evolutionary theory that Darwin proposed can be summarized thus:
Observation Number 1:
All organisms have the capacity to reproduce exponentially. This means that populations would grow to enormous sizes in just a few generations, unless something prevented them from reproducing at their full capacities. Observation Number 2:
The resources organisms need in order to survive and reproduce are necessarily limited in supply.Conclusion Number 1:
Since resources are necessarily limited, there must be competition within populations for those limited resources. Otherwise, the populations would grow forever, which clearly does not happen. In short, not every individual will be able to get the resources it needs in order to survive and reproduce.
Observation Number 3:
Organisms within a population are variable – that is, different individuals have different traits. Some of these variations will happen to be advantageous to their bearers; some will be disadvantageous to their bearers; some will have no effect at all. Whether a variation is advantageous, neutral, or disadvantageous is determined by how it affects an organism’s ability to survive and reproduce. Observation Number 4:
Organisms are more likely to resemble their parents than others in the population. This is inheritance. Typically this is due to genetic material (usually DNA) that is passed from the parents to the children.Conclusion Number 2:
Those individuals who happen to inherit traits that make them better suited to their environment will generally be better competitors for limited resources than those who happen to inherit traits that are less well suited to the environment. Therefore those organisms that inherit advantageous traits are more likely to survive and reproduce (and potentially pass on those traits) than those who inherit disadvantageous traits. This phenomenon is called natural selection.
Conclusion Number 3:
Since those individuals in a population who are best suited to their environment will pass on more traits (on average) than those who are less suited to their environment, the population’s heritable makeup will inevitably change over time. Advantageous traits will tend to become more common, while disadvantageous traits will tend to become less common. This phenomenon is called evolution.
This very simple series of observations and conclusions forms the core of modern evolutionary theory. The logic of the theory is very simple and yet very powerful:
if populations have the capacity for exponential growth (they do) and
if resources are limited in supply (they are), then there
must be competition for those limited resources – and not everyone will get what they need to survive and reproduce at their full capacity.
If there is competition for resources (there is) and
if individuals within a population are variable (they are) and
if some variants are better able to secure resources than are others (they are), and
if traits can be passed from parent to offspring (they can be), then it
must be the case that some traits are more likely to be passed on to offspring than are others, since the bearers of advantageous traits are more likely to survive and reproduce than are the bearers of disadvantageous traits.
If a population is experiencing natural selection – that is, if the bearers of some traits are more likely to survive and reproduce than are the bearers of other traits – then the population’s genetic makeup
must change over time as a result. That is, it will necessarily
evolve.
Let’s consider each of the key observations and conclusions that form the basis of modern evolutionary theory in a bit more detail.
Observation Number 1: Exponential Growth of Populations:
Populations grow
exponentially when resources are “unlimited” in supply. In practice, exponential growth means that the larger a population is, the faster it grows. This is true because the more individuals there are in a population, the more babies are being produced – and so, the faster the population grows.
This means that populations grow slowly at first, since there are few individuals producing offspring, but if they continue to grow exponentially, they eventually reach a point where they’re growing very rapidly indeed.
Even if we consider very slowly reproducing organisms, the offspring of a single pair would inevitably cover the entire planet in just a few generations if they reproduced to their full capacity. Let’s consider elephants, for example.
The female African Elephant starts reproducing by 10 - 12 years of age, typically has a single calf every 4 - 9 years, and lives up to 70 years. So, let’s start with a single pair of elephants. We’ll assume that each female starts reproducing at 12 years of age and produces one calf every 6 years until she reaches 70. We’ll further assume that half the calves produced are males and half are females. These are very conservative estimates, by the way.
Starting with just two 12-year-old elephants, in just 1,002 years there would be 2.06 x 10
18 elephants running around! That’s 2,060,000,000,000,000,000 elephants! In only 4,000 years, there would be 3.33 x 10
44 elephants! If the average elephant weighs 5 tons, the total mass of elephants after just 4,000 years of exponential growth would be about 1.66 x 10
45 tons!
That’s
billions of times heavier than the entire
solar system!
Clearly, despite the
capacity of populations for exponential growth, real-world populations cannot experience exponential growth for very long. The reason is because any exponentially-growing population will quickly run out of resources.
Observation Number 2: Resources are Limited:
“Resources” are anything that organisms need in order to survive and reproduce. Food, water, and living space are obviously resources. Mates are also resources (for sexually-reproducing organisms), because one cannot successfully reproduce without a mate. The Earth’s size is finite. Obviously, therefore, resources are limited in supply. This means that unrestricted population growth cannot occur indefinitely.
Conclusion Number 1: Competition for Limited Resources:
Since infinite resources are not available, a growing population will inevitably reach a point where the available resources are insufficient to meet the needs of every individual born into that population. So, individuals must
compete for resources.
This competition is not necessarily overt. Certainly, if two male deer are fighting for the opportunity to mate with a doe, they’re in direct competition for a resource, but this is the exception, not the rule. A much more common example of competition for resources would be that of two plants growing side-by-side. The two
are competing for the same resources – in this case, nutrients in the soil – even though they certainly aren’t fighting with each other. If one has a more extensive root system and so can absorb nutrients from the soil more efficiently, it will be a better competitor, and will probably be healthier than the other.
If individuals are competing for resources, then some will inevitably do better than others, and so the resources will be distributed unequally. Some individuals will fail to acquire the resources they need in order to survive and/or reproduce.
Observation Number 3: Variability between Individuals:
If you observe a population of organisms carefully, it soon becomes clear that the individuals are not all identical. Some traits are clearly advantageous to their bearers, while others are clearly disadvantageous. For example, other factors being equal, you would expect an antelope that runs faster than others to have an advantage over its fellows, since it will be less likely to be caught and killed by a predator. On the other hand, an unusually slow antelope is quite likely to die a premature death at the paws of a predator.
A more subtle example would be coloration in birds. Suppose female birds of a given species prefer to mate with brightly colored males. Since this is true in many species, it’s not a trivial example. If one male is brightly colored, he has a much better chance of securing a mate than does a dull-colored male. In this case, it’s advantageous to be brightly colored, and disadvantageous to be dull-colored.
Of course, a trait that is advantageous in one environment might provide no particular benefits in a different environment. In fact, it might even be disadvantageous. This is an important point: it’s the
environment that determines whether a trait is advantageous, neutral, or disadvantageous.
Those fortunate individuals who happen to possess traits that make them well-suited to their environment are said to be
fit. Specifically, an organism’s
fitness is a measure of how well the organism survives and reproduces in a given environment. Fitness is always a relative state, since the relevant question is: “How successful is this individual in reproducing (and thus passing on its good traits)
compared to others in the population?” An organism might produce 1,000 offspring, but that doesn’t mean it has high fitness – it can only have
more or less fitness relative to other members of the population. In other words, fitness is a measure of an individual’s heritable contribution to future generations. Obviously, the “fittest” individuals are those who make the greatest contribution of their traits to future generations.
Observation Number 4: Some Traits Can be Passed on to Offspring:
Genes influence the traits that organisms have. (There are other factors as well.) For example, genes influence such traits as your height, build, hair color, eye color, blood type, and so forth. Typically, each individual animal or plant carries two genes for each particular trait – one gene inherited from the mother, and one gene inherited from the father. Take the trait of blood type in humans. You might inherit an “A” gene from your mother and a “B” gene from your father; if so, you would have the genes “A” and “B” for the trait of blood type, and so you would have type AB blood.
Within the population as a whole, there may be many different genes for the trait in question. For example, there are “O” genes for human blood type as well. So, humans have three different genes for blood type – though obviously, no one person can carry more than two of those genes, since you inherit only one gene for that trait from each of your two parents.
All the genes possessed by an individual make up his or her
genome. Collectively, all the genes found in an entire population make up what is referred to as the
gene pool. For any given genetic trait, the variant genes within the gene pool are known as
alleles.
Genes are passed on (more or less) intact from parents to offspring. They are generally either inherited whole or not at all, and genetic inheritance thus is not a
blending of your parents’ genomes, but a
sampling from each of them. The chance that you’ll happen to inherit any
particular allele possessed by one of your parents is 50%.
Conclusion Number 2: Differential Survival and Reproduction (Natural Selection):
Clearly, some versions of a particular gene make their bearers better suited to their environment than do others. That is natural selection in a nutshell. Those alleles that make their bearers better-suited to their environment are more likely to be passed on to offspring than are alleles that make their bearers poorly-suited to their environment. (Alleles, you recall, are variant versions of the same gene. The A, B, and O blood types are each produced by different alleles of the “blood type” gene.) More precisely, individuals that happen to be well-suited to their environment (for whatever reasons) are more likely to survive and reproduce than those that aren’t.
An example may help to clarify the reasoning. Imagine a population of hares living in an Arctic region, where snow covers the ground for most of the year. If all the hares in this population are the same shade of brown, then there is no variation in coat color, and there can be no natural selection on this trait. Now imagine that a mutation occurs which creates a new allele (something mutations are indeed capable of doing), and that this allele causes its bearers’ fur to turn white. Obviously, these white hares are less likely to be seen and killed by predators in a snowy landscape than are their brown companions. So,
on average, a white hare is more likely to live long-enough to reproduce than is a brown hare. Therefore, the average white hare will produce more offspring than the average brown one.
It’s important to keep in mind that natural selection is not so much a process as a statistical effect. It’s not like predators consciously pick and choose which prey animals will survive long enough to reproduce, for example. Rather, those prey animals that are less fast/wary/camouflaged/etc. than average are more likely to be caught and killed, and so less likely to pass on the genes for those unfit traits.
In short,
if there is competition for resources (there is), and
if organisms are variable (they are), and
if this variability affects individuals’ abilities to survive and reproduce (it does), then natural selection is an inevitable result.
Conclusion Number 3: Natural Selection Causes Populations to Change Over Time – That is, Evolve:
Clearly, if a given allele makes its bearers more likely to survive and reproduce than the average member of the population (and thus pass the allele to offspring), that allele will tend to become more common over time. On the other hand, if the allele makes its bearers
less likely to survive and reproduce than the average member of the population, that allele will tend to become less common over time and might eventually disappear from the population completely.
In the example of the hares above, the “white fur” gene will become relatively more common over time, because its bearers are more likely to pass it on than the bearers of the “brown fur” gene are to pass
it on. Since the total percentage of genes must be 100%, if the “white fur” gene is becoming relatively more common, the “brown fur” gene must become relatively rarer.
Of course, the environmental conditions at the time are what determine whether an allele is beneficial, neutral, or harmful to its bearers. In the example above, the hares only benefit from having white fur because their environment is predominantly white. If they lived in an environment without snow, the white fur trait would be disadvantageous and would not be selected.
So, the genetic makeup of the population can change over time as a result of natural selection. Beneficial alleles become more common, while less advantageous alleles become rarer.
This change in the heritable makeup of a population over time is
evolution.
Is Evolution a Legitimate Scientific Theory?:
A scientific theory, as you recall, is an
explanation for some observed phenomenon – e.g. evolution. Without going into all the gory details, working scientists are more or less in universal agreement that any useful and legitimate scientific theory must satisfy three criteria: it must be
testable, it must be
falsifiable, and it must be
predictive.
Testability and falsifiability are two closely-related concepts. When we say that a theory is
testable, we mean that we can devise empirical observations and/or experiments to test the theory. If the observations and experiments do not support the theory, then the theory must be modified or discarded. Any theory which cannot be tested is of little or no use. For example, I may have a “theory” that grass is green because God happens to like that color, but since I have no way to test that “theory,” it’s of no use.
Any useful scientific theory must be, in principle, falsifiable. In other words, if the theory
is false, there must be some way to
demonstrate its falsity through observation and/or experimentation. Suppose I have a “theory” that the Universe was created 0.002 seconds ago, complete with an overwhelming amount of false “evidence” of an ancient history, including our memories of events that never actually occurred. Well, it’s an interesting idea I suppose, but it’s useless as a scientific theory, because there’s no way to prove it false, even if it is. If no conceivable observation or experiment could prove the “theory” is
false, then there’s no way to properly test it, and so there’s no particular reason to believe that the “theory” is
true.
Any scientific “theory” which makes no predictions is – at best – just so much intellectual masturbation. It may be interesting, but it accomplishes nothing.
So, how does evolutionary theory hold up as a scientific theory? Is it
falsifiable? Of course it is. It would be ridiculously easy to falsify evolution as a theory. For example, one of the
predictions of evolutionary theory was that there must be some molecular mechanism that allowed traits to be passed on more or less intact from parent to offspring, and not blended. (If offspring were simply a blending of their parents’ traits, all variability within populations would soon be blended away, and without variation, there could be no selection and therefore no evolution.) In the 1950s, it was discovered that DNA encodes genetic traits and allows them to be passed on from parents to offspring intact.
Biologists further predicted that there would be a correlation between how closely-related organisms appeared to be, and the similarity of their DNA. Specifically, it was predicted that those organisms which comparative anatomy, the fossil record, and comparative behavior suggested were close relatives would share very similar DNA (since they share recent common ancestors), while organisms which appeared to be very
different would have dissimilar DNA (because they share more ancient common ancestors). Exactly as predicted, molecular analyses showed beyond any doubt that those organisms which independent lines of evidence suggested were closely-related
were closely-related, according to the DNA evidence. Had the DNA turned out otherwise, this would have been a deathblow to evolutionary theory. We would have had to go back to the drawing board.
Another very easy way to falsify evolutionary theory would be to find fossils where they couldn’t possibly exist, according to the theory. The existence of fossils of modern mammals in Precambrian sediments, for example, would immediately falsify evolutionary theory. Interestingly, no such “out of place” fossils have ever been found, despite decades of diligent searching.
Is evolutionary theory
testable? Again, of course it is. The discovery of DNA and its use to test specific predictions of evolutionary theory provides a perfect example of how it can be – and has been – tested. Had the theory failed the test, we would have had to scrap it (or at the very least, heavily modify it) and start over.
Does evolutionary theory make predictions, and do those predictions hold up? Again, yes. The DNA examples cited above are examples of predictions made by evolutionary theory which were completely borne out by the data. For a more prosaic example, consider the moth
Xanthopan morgani praedicta. Darwin himself used evolutionary theory to predict the existence and properties of this moth species, which is why it’s name includes the term “
praedicta.” The moth was discovered and named some 40 years after Darwin’s prediction, and it had exactly the properties that Darwin had predicted. Recently, biologists working in the Caribbean Islands predicted the existence of a then-unknown lizard species from evolutionary principles, based upon genetic studies of known lizard species. Within a few years, the predicted species was discovered, and it had precisely the properties that had been predicted.
Maybe these predictions are less than convincing, so here’s a really
good one.
If it’s true that extant species are the result of common descent (as opposed to special creation), then it should be true that independent methods of deriving phylogenetic trees to show the relationships between organisms should come up with the same results. If species are
not related by common descent, then there’s no reason to expect independent methods to derive the same phylogenetic trees for any given group of species.
(A phylogenetic tree is a “family tree” showing how groups of species are related to each other. It’s exactly analogous to a family tree that is used to show how people are related to each other.)
Okay, here are some numbers to think about – the number of possible phylogenetic trees for just 20 species is 8,200,794,532,637,891,559,375 (!). I think that any reasonable person would agree with the conclusion that two independent methods of deriving phylogenetic trees would
never produce the same tree twice, even if the researcher in question spent every waking moment of his or her life doing these trees with the fastest computers available –
if the trees did not indicate real relationships, that is.
Guess what? When independent methods are used to derive phylogenetic trees, they
almost always produce the
exact same trees. The odds that these trees should be produced by chance, and that they don’t indicate real relationships are literally astronomical.
Either species
really are linked by common descent or the Creators have gone to an
extraordinary amount of trouble to make it look as if they are!
Consider these three animals:
Animals “A” and “C” live in very similar environments and have very similar lifestyles. (They’re both burrowers.) Unsurprisingly, then, both look very similar to each other. This is a straightforward prediction of evolutionary theory; organisms adapted for the same or very similar environments will tend to evolve to look very similar.
However, “A” and “C” are not
at all related to each other, as is revealed by their internal anatomy. “A” and “C,” in fact, are about as far apart from each other in terms of relatedness as two animals can be and still both be animals. “A” is a
caecilian, a member of an amphibian lineage that has adapted to a life of burrowing underground and has lost its legs (and in most species, its eyes). “C” is an earthworm.
Biologists have known that caecilians are amphibians since long before it was possible to compare the genetic makeup of organisms. Since, according to evolutionary theory, all extant organisms are related by common descent, the theory predicts that the caecilian should have little in common with the earthworm, despite their great physical similarities, and a great deal in common with the frog, despite their dissimilar anatomies. Sure enough, genetic analyses confirm that prediction.
Creationists often argue that the striking genetic similarities between “closely-related” organisms (say, chimpanzees and humans) are simply due to the Creator(s) re-using genes to build similar structures, and have nothing to do with common descent. Things like caecilians and earthworms – which are superficially very similar and share many common features, but are
not closely-related and therefore don’t share common genes – demonstrate the inadequacy of this totally
ad hoc “explanation.”
Here’s another trio of animals to consider:
Which two of these three animals are closely-related, and which of them is only distantly related to the other two?
The bird and the crocodile are both
archosaurs, as is revealed by examination of their skulls, their jaws, and their leg joints –
and by the fossil record. The Komodo dragon is a lizard, a
lepidosaur. The bird and crocodile are
much more closely-related to each other than either is to the lizard, despite the superficial similarities between the lizard and the crocodile.
This was known since before Darwin’s time (Darwin’s contemporary, T. H. Huxley, noted that birds are just “glorified reptiles”), based on careful studies of the anatomy and developmental biology of these various animal groups. Again, a straightforward prediction of evolutionary theory is that the bird and crocodile should be much more similar genetically than are the crocodile and the lizard – despite the superficial similarities between the crocodile and the lizard. Sure enough, genetic analyses confirm the close relationship between birds and crocodilians.
The first true fishes were the
agnathans, commonly known as the “jawless fishes.” Here is a picture of a surviving agnathan, a Sea Lamprey.
Both the fossil record and living agnathans indicate that the earliest fishes had
seven gill arches. These are the jointed structures in fishes that support the gills. (Note the external gill openings on the lamprey, showing that it has seven pairs of gills.)
The descendents of the agnathans are the
gnathostomes, the jawed vertebrates. Living jawed fishes have
five gill arches, instead of seven. You can see that in this picture of a shark.
Examination of the development of jawed vertebrates shows that the first gill arch has been modified to form the jaw, and the second gill arch has been modified to form the
hyoid apparatus, which supports the tongue. This explains why modern jawed fishes have five gill arches.
According to evolutionary theory, there must at some time have been fishes with
six pairs of gill arches. Sure enough, fossils have been found of fishes that had six gill arches and jaw, but lacked a hyoid apparatus. Perhaps even more impressively, some “primitive” sharks have been discovered that have six gill arches and no hyoid apparatus.
On Biological Evolution (1)
His secrets are not sold cheaply.
--Liv
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