I’ve decided that a good way to start off this tumblr is to give an introductory “lesson” on what evolutionary theory is. It is arguably the theory which is most misunderstood by the American public, perhaps only trailing behind quantum theories. Unfortunately, people in America seem to have more trouble with the fact that organisms change over time than with the fact that electrons can sometimes be in two DIFFERENT states in one time. Therefore, I think it is important to show what evolution is and how it works.
The theory of evolution is the underlying theory which connects all of the biological sciences. Evolution is as important to biology as Einstein’s relativity is to physics. Evolution can be defined many ways, the broadest definition being a change in allele frequency over time.
All organisms contain Deoxyribonucleic acid (DNA). DNA is stored in each of our cells as chromosomes. Humans have 23 pairs of chromosomes; we inherit one from our father and the other from our mother (In reality it is more complicated but for now, this will do). Strings of DNA which perform a specific function are called genes. Each gene has variations called alleles and one copy of an allele can be found on one pair of chromosome. These alleles account for all of the physical traits seen in organisms, from chemical secretion to fur. Gene variation occurs from “mistakes” during the replication process, however, these “mistakes” are important for evolution to occur because it is the allele which allows the organism to survive which will be passed on to future generations. This is called natural selection and it is the most supported mechanism of evolution. Genes which allow the individual to survive up until reproduction will be passed to its offspring. This is sometimes referred to as “survival of the fittest.” Although everyone attributes this to Darwinian evolution, Darwin himself never used this term. It is possible that being weak may be more beneficial to an individual than being strong/fit. Anyway, here’s an example of natural selection in action (and one that every biology student is sick of hearing about).
The peppered moth (Biston betularia) comes in two possible colors, white and black. In pre-industrial England, naturalists noted that the majority of peppered moths were white. After the industrial revolution, the populations began to shift, and black moths were becoming more numerous than white moths. So what happened?
Peppered moths rest on the lichens of trees as camouflage to predators, mostly birds. Lichen is white(ish) so the peppered moths which were more suitably camouflaged would probably be missed by the birds which feed on them. On the other hand, the black moths were sitting ducks because they could not camouflage against the lichen. Years after the industrial revolution, the amount of lichens on the trees began to diminish and the bark of trees became more exposed. Now, the black moths were hidden to the eyes of predators instead of the white moths so the populations began to shift towards black moths because they were not getting eaten and therefore, were making more baby moths than the white ones.
This example has lost merit because we have learned that birds actually see in ultraviolet light, and not in the color spectrum that we humans see in. Nonetheless, it still is an excellent example to illustrate how natural selection works.
So there is how that definition of evolution works, but what accounts for the development of new species. This is a common question asked by young earth creationists (YEC): Evolution can explain minor variations among species, but how does it explain new species? Evolution shows “micro-evolution” but what about “macro-evolution?” The quickest answer to this: the same exact way.
Evolution can account for the development of new species. One easy way to see this is to imagine a population becoming separated in some way, let’s say, geographical (a river divides two populations of the same species). The individuals of each respective population on either side of that river will only be able to mate with each other and not mate with their old friends on the other side of the river. Therefore, the genes which will become more prevalent in either populations will be different based on the different environments on either side of the divide. Over time, the differences that build up, from population to population, will become so drastic that if the two populations were to ever meet again, they will most likely not be able to mate with each other to produce fertile offspring. This is the common definition for the term species. This is how natural selection can produce macro-evolution as well as micro-evolution. But I hate this distinction, micro and macro evolution are the same thing, and here is why…
Homo habilis is the first recognized species of the genus Homo and one of our ancestors who lived about 2 million years ago. When looking at fossils, it is obvious that H. habilis is a different species than modern humans, Homo sapiens. However, imagine if you could hold hands with your mother, and she could hands with her mother, and she could hold hands with her mother, and so forth all the way to Homo habilis. If you were to examine this very long matrilineal chain, you would never be able to make a clear distinction between one species and another. Each individual would look a lot like her mother and her daughter. The changes in morphology would have been a very slow and gradual change, what most would call micro-evolution. However, these gradual changes still produced what we would call a different species. Unless of course you want to consider this guy human.
So there you have it. That is evolution in a nutshell. My next post will be examples of the massive amounts of evidence biology as mustered up to support evolution and then I will probably make a post which will deal with responses to common YEC claims. For a preview, I recommend this hilarious video:
