We have had several conversations on this site over the years on the subject of macroevolution. Many of the comments affirming macroevolution have come from a very loyal and courteous participant here, atheist “Tim D” (full name Tim Duck). I offered Tim some posting space (rather than just in the comments section) to make a positive case for the theory that all new life forms arose from a single common ancestor by unguided natural processes.
Just to be clear, the post below is by atheist, Mr. Tim Duck. He welcomes your comments.
Why I Think MacroEvolution is True
By Tim Duck
Short foreword: a while back I was challenged to write a short article in defense of the theory of evolution by natural selection (sometimes called “Darwinian evolution”) for this site. I felt confident that I could do so, but once I sat down, I found a lot of difficulty stringing all the concepts in my head together into a coherent series of paragraphs, and when I tried, I ended up with 10+ pages. I realized, my mistake was that I was trying to give a comprehensive rundown of all the arguments for and against the theory, from scientific and religious circles, that I have encountered. That’s simply not practical, so instead what I’m going to focus on here is a description of the most fundamental, underlying principles of the theory — the simplest, most basic aspects that come together to form evolutionary theory. This is a straightforward approach that should cover most questions that people would have; and I have been told that if there are any questions not answered herein, that I will have the opportunity to respond to them in the comments section, which I will try to the best of my ability to do faithfully.
Before I can say anything about evolutionary theory, I must ask: What is it, exactly? There’s certainly a lot of confusion on this point — what does evolution say about the origin of the universe? What implications does it have for the existence of god, or of objectively-grounded morality? What does it say about us as humans? These are all interesting questions that we hear a lot, but before we can answer any of them, we must define evolution in a fundamental, principled way. First and foremost, though, we use the tentative definition that evolution is the shift in the genetic “norm” of a population of organisms.
Evolution ultimately starts at the molecular level — DNA. Most people are familiar with the basic features of DNA — you find it in stringy things called “chromosomes” (each one of which is composed of a long series of smaller units called “nucleotides,” which can number 100 thousand to 10 billion) that reside within cell “nuclei,” or cores. DNA contains segments of nucleotides called “genes,” which are responsible for all the traits of a single organism, so any living thing has genes and thus DNA. Without genes and DNA, a discussion of evolution would be moot.
“Nucleotides” are small molecules built up of a sugar (ribose or deoxyribose), a nitrogenous base, and a phosphate group. There are four basic types of nucelotides: adenine, guanine, thymine, and cytosine (abbreviated “A, G, T, and C”). The sugar (ribose in the case of DNA) forms the “backbone” (and gives the chromosome its Jacob’s-Ladder structure), and the phosphate group accounts for the reaction that binds the nucleotides together.via something called a “phosphodiester bond.” Furthermore, T only bonds with A and G only bonds with C; when we have long strands of these polymers, we have genes, the fundamental unit of DNA.
But what kind of traits do genes determine? Well….everything. Every single physical characteristic of both you and I is ultimately determined at the genetic level — it can be a small trait that is almost universal within a population of humans, such as protein production at the cellular level, or it can be a much “larger” trait (such as eye color or bone structure) that is made up of many smaller traits at the cellular and molecular level. To simplify, you might say that the “gene” is the “unit” of genetic variation — even traits such as hair or skin color can be broken down into smaller individual traits which exist at the genetic level. What this means is, there is not a “hair color gene” or a “bone structure gene,” or a “body type gene.” These larger traits can be thought of as “trait groups,” and ultimately rely on a convergence of smaller gene groups within DNA. So ultimately, if a trait changes somehow from generation to generation, it happens at the genetic level.
The way in which genes do this is not direct, though — a gene does not contain information which says, “this person will have red hair, so work with these other genes to make red hair.” Rather, a gene in itself contains only very simple (I use the word simple here liberally) chemicals which are used to do things like encode proteins. This makes it difficult to see what a gene will do if you only look at it at the genetic level. We are able to identify certain genes (such as those responsible for Alzheimer’s and Tay-Sachs disease) because of a careful, experimental process of elimination and isolation which is far too complicated to go into detail here….but basically, a single gene by itself can only do so much. If it’s defective or mutated, it can cause some serious changes (or even problems), but it won’t cause a human to be born as a gorilla or something silly like that. Most such changes, you might not even notice.
So, skipping ahead for a moment…humans reproduce sexually, of course. At the cellular level, what happens when a sperm and egg cell join together during the process of fertilization and conception is known as “sexual recombination” or “genetic recombination.” This is when trait genes from each of the parents’ DNA are “shuffled” in a way that is basically random, and then combined to form a new sequence that will be the offspring — it is by this process that we inherit certain traits or trait groups from both parents (such as eye color or facial similarity), and yet we don’t usually look exactly like either of our parents; we have traits from both, but not ALL traits from either individual.
So what happens, then, to the genes that we don’t acquire from our parents? If my father has red hair and my mother has blonde hair, and I’m born with red hair, what does that say about my mother’s blonde hair? A number of things can happen. Some genes are called “recessive,” which means, they do not manifest if they are coupled with other “dominant” genes. They must be paired with other similar “recessive” genes before they are manifest — diseases such as Tay-sachs can occur in this way; if both parents have the same recessive gene, then the child has a much higher chance of contracting the disease. In this way, an offspring can spread a gene for several generations without ever directly seeing or feeling its effects. So even if a gene is not active or dominant, it can still be passed on.
Okay, the story so far: (1) all life has DNA, (2) DNA is shuffled randomly during sexual reproduction, (3) this causes a rotation of traits within the offspring. This is the natural process that establishes what we call “genetic norms” in a population — popular traits or trait groups that are almost universal, or at least prevalent, in a population. In humans, for instance, having two arms, two legs, a head, and a torso is considered a “norm.” There are some variations from this norm, such as people with extra or missing parts, but this is the most prevalent template for human development (On a side note, please do not confuse the term “genetic norm” with the term “social norm;” they are two very different concepts!).
This is a microcosm of what happens during evolution, but in this case it doesn’t give us a wide enough pool of genetic diversity to account for rapid or drastic evolution within a population — a single population in a single area, such as humans in a city, probably won’t see much of a drastic change even over long periods of time. So, how do we get from here to “the big picture” of evolution in action? To answer that question, we’ll analyze another objection that’s often raised by critics of evolutionary theory: That’s just microevolution. What evidence do we have that macroevolution takes place?
Going back to the original definition for a moment, you may recall that I said, “evolution is the shift in the genetic norm of a population.” What this means is, at the most fundamental level, there is no difference between ‘macroevolution’ and ‘microevolution.’ Macroevolution just means, “a large shift in the genetic norm,” whereas microevolution means, “a small shift in the genetic norm.” Even if I do offer you a concrete example of each (macro and micro), if we break them both down, we will see that they are identical at the genetic level. The only difference between the two is time — small changes happen all the time and are mostly benign (i.e. they don’t have any visible effect on our bodies), but that is because they are made up of small amounts of genes. Large changes happen less frequently because they must accumulate over time. If small changes can happen, and small changes can accumulate, then it follows naturally that they can accumulate over large periods of time. That is why you only see truly vast differences in traits between species which exist hundreds-of-thousands, or millions, of years apart.
But how does “macroevolution” occur? How do large changes to an organism happen? There is a famous example called the Lenski Bacteria Experiment; I don’t have time to detail it too much here, but basically, 12 “tribes” of the exact same strain of e. coli bacteria were isolated in 12 containers and provided with nutrients, glucose and citrate. Each day, each “tribe” was moved to a new container and provided with new nutrients. Now normally, e. coli can’t digest citrate, and so they only “ate” the glucose, and once the glucose in the container ran out, their numbers would start to dwindle. However, one day, after a significant amount of generations (over 20,000), suddenly, one of the 12 tribe cultures suddenly began to reproduce at an exponential rate, even as the other tribes had run out of glucose and began to dwindle! After subsequent research it was determined that this mutant strain of e. coli had mutated a particular structure within its body which allowed it to process citrate as well as glucose, so it was able to get almost twice as much out of its environment as the other tribes. Through further study they managed to isolate the gene which was actually responsible for the mutation (call it “mutation B”)….and yet, the mutant tribe was not the only tribe with this gene. So what gives? As it turns out, after examining samples saved from each prior generation before the mutation occurred, it was determined that a mutation had occurred around generation 20,000 (call it “mutation A”) which had no significant effect on its own, but that when paired with mutation B, caused the citrate mutation to occur. So the bacteria needed not only to have both A and B, but to have them in a certain order (A, then B). Only then would the new trait manifest.
I use this experiment to demonstrate one important thing: Large mutations are made up of smaller mutations. They also take much more time; most of the cultures in that experiment mutated either A or B on their own, but only the one that mutated first A and then B was able to experience the citrate mutation. In this case the effect seemed small because the organism was single-celled, but this principle applies equally to all organisms; it’s just a combination of a few basic points:
(1) if I have a trait, then like the bacteria culture, there is a chance that I may pass it on to my children. This can be true for more than one trait, of course; I could pass on thousands of traits to my children.
(2) if my child receives a trait from me, he/she could pass it on to his/her children; this is also true for more than one trait, my child could pass on thousands of other traits, some from his/her mother and some from me
(3) if at any point, any traits mutate, those traits will be preserved if they are passed on (i.e. the mutated trait will pass on, not the original unmutated one).
Through this process, a series of small, individual mutations can accumulate over a very long time. Even in a single population this can produce some genetic diversity….but again, not really enough to account for a drastic shift of the sort you might call “macroevolution.” No, what we need is a diversity of two things: (1) population, and (2) habitat. In a small town in Colorado, you’re not likely to find much genetic diversity just by looking at people. You’ll mostly see people of similar ethnicity with similar features. Likewise, in a small village in Egypt or Uganda, you’re not likely to find many different kinds of ethnicity or massive variation. However, if you compare the two — smalltown Colorado with village in Egypt or Uganda — you will see that the two communities are quite ethnically different. There is a definite variation in the norms between these two areas; darker vs. lighter skin being the most noticeable. That is a small difference, but it makes a good segue into the last example I have for now.
Probably one of the most important things to remember about evolution is this: it is about divergence, not progression. To “evolve” does not mean “to get stronger,” or “to get better,” or to “improve.” It simply means to “change.” Divergent species of the same ilk can have their own unique strengths and weaknesses, which better suits them to some situations but may even worsen their ability to deal with others. So there is no such thing as the “ultimate species” in that sense, despite what horror movies about biologists run amok would have you believe. A good example of this is the Pod Mrcaru/Pod Kopiste island lizards. In 1971, a group of scientists transported five couples of Podarcis sicula lizards (native to Pod Kopiste) over to Pod Mrcaru, a nearby island with a slightly different environmental culture, and released them. Another group of scientists came back in 2008 to check on the lizards, performing DNA tests of samples captured from the wild to ascertain that (A) yes, the lizards they were seeing were descendants of the Pod Kopiste Podarcis sicula, and (B) the lizards had spread out and populated the island. The lizards from Pod Kopiste, while bearing almost identical genetic profiles, exhibited a few differences from their “ancestors” on the neighbor island — chiefly, a larger head size. The payoff being increased bite force, the downside being that the head is bigger, and thus takes more power to maneuver, requiring stronger neck and jaw muscles. This resulted in the lizards having a more vegetarian diet, possibly due to their lack of a strong body — chasing mobile prey would be markedly more difficult with a larger head and small body.
There are really more examples I would like to go into, but for the sake of brevity I’m trying to focus only on those absolutely necessary to define evolution….and so in closing, I will come back to my introductory (rhetorical) questions, and address some common errors/falsehoods that are frequently spread about evolutionary theory (and the people who accept it):
-) Evolution is not a theory of origins; it does not address (or attempt to address) where the universe came from, or where life came from. It is only the study of living things and how they change over time. Abiogenesis is a separate theory that deals will the origin of life, completely independent of evolutionary theory. Within the context of evolutionary theory itself, it is entirely technically possible that someone like a god created the first life. All evolution does is trace what happens after that.
-) If evolution is true, that does not mean that god does not exist. It may challenge some specific claims made by certain interpretations of religions or texts (such that “god created humans in their present state 6000 years ago”), but since evolution does not address any of the fundamental characteristics of god (who is said to be “timeless, spaceless and immaterial”), it can’t be said to challenge them in any real way.
-) If someone accepts evolution, that does not mean they support a “survival of the fittest” worldview. Evolution is a descriptive theory, not a prescriptive theory. It does not tell us what we “should” do in the future, and it does not advise us to “evolve ourselves” such as through eugenics. If someone uses evolution as a basis on which to declare racial superiority or inferiority, then he/she probably knows very little about evolution at all. To say that “evolution is not true because it promotes [x worldview]” is no stranger a statement than to say, “shotguns don’t actually work because shooting someone in the face promotes violence.” Evolution is merely a tool by which we hope to understand the workings of biology a little better.
I guess that’s about it….I know I haven’t addressed *all* of the criticisms that are out there, but I hope I have provided at least a basic groundwork on which to base any further discussion of evolutionary theory. If you have any questions or comments, then perhaps I can tweak things in the future so as to provide an adequate attempt at a follow-up. And of course a thanks to Mr. Turek for inviting me to write this as a guest on his site!
Free CrossExamined.org Resource
Get the first chapter of "Stealing From God: Why Atheists Need God to Make Their Case" in PDF.