Natural selection is the engine of evolution. Regardless if one is talking about micro or macro evolution, natural selection is what makes it go. It is often referred to as survival of the fittest. We can see selection going on around us. A prime example is how the population of an organism changes during selection. Each species has enormous potential whether it is disease resistance of on individual over another or resistance to antibiotics in a particular bacterium. This diversity allows species to survive.
Each individual in a species is just a bit different. Maybe one has a longer neck or is a bit faster. One might have a slightly different coloration. It is this difference that natural selection works with and if one of the differences gives that individual some benefit over the others then they have a better chance of reproducing and passing this trait on. How do these differences come about? Most are due to mutations in the genome but in some cases, single celled organism, genes can be passed from one individual to another. Once we get passed the unicellular it is mutation that brings about the difference. Mutation however is slow, undirected and most often harmful. The fact is that over 70% of all mutations are harmful if not fatal to the organism. In order to change from one species to another, enormous amount of time is involved.
Natural selection has some problems. First, some trait has to first exist in order to be selected. Natural selection cannot look to the future or plan. It cannot select something in order for another mutation to take advantage of. It is random. Next, just because a trait provides a benefit does not mean it will be passed on to future generations. The individual may die before it can reproduce. The trait may lie on a recessive gene and not be passed on to others.
Every example I have ever seen for natural selection is based on microevolution, that is change within a species. In most instances, the population still has individuals with and without the desired trait. I will give two examples, the first has been in every basic biology textbook since the 1960’s. That is the peppered moth. For those who are unfamiliar with this example, the peppered moth had two varieties, one that was basically white with black spots and the other black with black spots. In England where coal fired plants produced electricity, ran machines and heated homes the trees where the moths lived and fed became covered with soot. This gave an advantage to the darker moths and they soon became the dominate variety. But, after the coal plants were cleaned up and the trees became less sooty, what happened? The lighter colored moths became dominate again. So the peppered moth stayed the same and the only change was the ratio between lighter and darker colored moths.
The next example is antibiotic resistant bacteria. In every strain these seems to be some bacteria that are naturally resistant to any antibiotic. Those resistant bacteria survive and reproduce while the others are killed. Still some bacteria that are not resistant survive. But even if they did not survive, the resistant bacteria are still the same species that existed at the start. If you start with a strep culture and keep introducing antibiotics you will end up with strep bacteria that are resistant but you will not end up with a bacteria that is not strep.
Species on the earth seem to have a remarkable amount of diversity within the species. The domestic dog is probably the best example I can think of. From the giant mastiffs and Saint Bernard’s to the tiny toy poodles and terriers all are dogs. They may look completely different but if allowed to interbreed that will revert back to original form.
As to macroevolution, it seems there are no examples to be found today. Species are remarkable stable. Dogs product dogs. Cats produce cats. Reptiles product reptiles and mammals produce mammals. Each according to its kind. We just do not see any new types of animals evolving and as to total new class of animal. But we are told to believe that this was going on in the past. That fish gave rise to amphibians that in turn gave rise to reptiles. The reptiles gave rise to both birds and mammals and the while we still have fish, amphibians, reptiles, birds and mammals.
I posed this example to a comment on my first post on evolution and got this reply. “Once a family of animals has begun to specialize its evolution only becomes more specific. The point is that our early ancestors were non-specialized, so birthed many family of animals. They also directed me to Google articles on phylogenetic trees to aid their argument. You can find one such article here, http://en.wikipedia.org/wiki/Phylogenetic_tree. However there seems to be a number of phylogenetic trees and not a great consensus on which one if any is correct. There are also limitations to such trees as you can see from this quote from the article “Although phylogenetic trees produced on the basis of sequenced genes or genomic data in different species can provide evolutionary insight, they have important limitations. They do not necessarily accurately represent the species evolutionary history. The data on which they are based is noisy; the analysis can be confounded by horizontal gene transfer, hybridisation between species that were not nearest neighbors on the tree before hybridisation takes place, convergent evolution, and conserved sequences.” Please refer to the entire article.
What I find troubling about this argument as to why macroevolution has “stopped” is twofold. First, dinosaurs were highly specialized and yet they were able to evolve into both birds and mammals. Their high specialization is showed by the wide variety of dinosaur species. The second problem is that this specialization argument is circular. Essentially it boils down to, why don’t mammals evolve into something different? Because they are too specialized. How do we know they are too specialized? Because they only produce more mammals.
It also ignores one of evolutions sacred cows, junk DNA. We are told that much of the DNA in species is so called junk DNA, that is it has not useful purpose and is a hold over form some distant ancestor. Yet if we still have all this useless DNA, then why can’t that junk mutate and give rise to another type of organism? Did mutations suddenly stop? If not then no matter how specialized an organism is it would seem to me that if the right mutation comes along it should still be selected and a new organism evolve and why not a new class. Or are the number of classes somehow preordained. If so by whom? Of course this also ignores new findings in the human genome that the so called junk DNA does indeed have a purpose and there may not be any junk. Junk DNA falls into the trap of thinking that because we do not know what a function something has it must not have a function. Of course it now appears that the so called junk DNA does indeed have functions. The Encode project, or Encyclopedia of DNA Elements, has found that almost 80% of the genome is biochemically active and they expect that eventually they will find that all or almost all of human DNA serves a useful purpose. You can read the Wall Street Journal article about the Encode project here http://online.wsj.com/article/SB10000872396390443589304577633560336453228.html or go to the Encode site here http://www.genome.gov/10005107 or for those who do all their research on Wikipedia here http://en.wikipedia.org/wiki/ENCODE .
I have to admit that this argument as to why we do not see new organisms or classes still arising also gave me a smile. This is just the exact argument that creationists have been making for centuries, kind only begets kind.
Natural selection works on the micro level; we have examples all around us. What we do not have are examples of natural selection working on the macro level to evolve new types. On the macro level the only thing I see working is the extinction of species as their environment changes or they are unable to adapt to humans. No clear examples exist of one type of organism evolving into another type. We are just asked to believe and have faith that some unidentified time in the future that all the missing information will be found.
Next time, think there are no problems with evolutionary theory? Guess again, Charles Darwin himself listed problems with his theory in his book The Origins of Species. These problems still exist but you will not find them mentioned in biology texts.
Have a blessed day,