An introduction to evolution

If some of the terminology here in the first few paragraphs is a bit daunting, don't sweat it. I will try and explain everything the best that I can. Also, if anything here isn't clear to you please let me know. I will try to clarify.

WHAT IS BIOLOGICAL EVOLUTION?

Biological evolution is defined as the change in genetic composition of a population over time. A population experiences some genetic variation through mutations and sexual recombination. Natural selection deletes harmful variations from the population. Aside from mutations and recombination in conjunction with natural selection, gene flow and genetic drift can also cause a population to evolve. When one population branches out from another, it may speciate if the two populations are geographically isolated.

The modern synthesis, in the context of evolution, refers to a comprehensive, unified theory of evolution encompassing information from a myriad of biological, as well as other, fields. The modern synthesis is the most widely accepted theory of evolution today. It consists of the ideas described above. The modern synthesis is modified with newer discoveries.

Evolution provides us with a simple, yet elegant explanation for the variety of life on earth. Applying the theory of evolution in conjunction with other information that we have gives us keen insights into the history and relatedness of all life on earth, as well as insights into things of a more practical nature for the common man, such as why certain bacteria do not respond to antibiotics anymore.

A BRIEF HISTORY OF EVOLUTION

Though I feel that the history of evolution is important from an academic standpoint, I will not go into much detail on it here. I would prefer that the main ideas of evolution are understood rather than the history of it. However, I will touch on some of the more important points that I feel should be common knowledge.

Charles Darwin is credited for discovering the theory of evolution with his publication of The Origin of Species in 1859, though he called it descent with modification rather than evolution. Darwin took a five year voyage on a ship known as the H.M.S. Beagle in 1831. On his voyage, he documented various interesting details in the fossil records that he saw and in the distribution of certain animals that he saw. Darwin conceived his theory of natural selection in 1838, however he did not publish it then for fear of being thought a heretic. Darwin continued his research, making him an established naturalist. In 1858 a man named Alfred Russel Wallace sent Darwin a paper describing ideas similar to his own. This prompted the two scientists to publish a joint paper on the subject. In 1859, Darwin published The Origin of Species. Within a decade of its publication, evolution had become the accepted paradigm in the biology community.

THE GENE

A gene is a collection of chemicals known as nucleotides. All the genes in our body cumulatively make our genome. Almost all types of cells in our body contain an entire copy of our genome. Genes are the code of life, telling cells what to do. Based on which genes are "turned on" in a particular cell, the cells of our body carry out the instructions that our genes have programmed into them. In this way, cells differentiate and come together to form different tissues, organs, organ systems, and organisms.

A nucleotide is made up of a base, a sugar, and a phosphate group. The base is what is important here. It can be one of four things. Three nucleotides together, known as a codon, code for the production of a chemical known as an amino acid. The sequence of nucleotide bases is what determines which amino acid will be coded for. Multiple amino acids, coded for by a sequence of codons, come together and form proteins, the workhorses of our cells. These proteins carry out the functions of life at the cellular level. On the larger level, all the innate characteristics that make you you are essentially the cumulative effects of these proteins.

Our genome is located in 23 pairs of chromosomes, each containing a molecule of DNA, which is just an enormous sequence of nucleotides. You receive 23 chromosomes, or about 50% of your DNA from each parent. In animals that reproduce sexually, a process known as crossing over, or sexual recombination occurs. Essentially, you don't receive an entire copy of any of your parents chromosomes. Rather, each chromosome that you receive is a combination of a pair of chromosomes in one of your parents. In other words, a parent's chromosomes pair up, shuffle genetic material amongst each other, and then pass the chromosome on to the child. This shuffling contributes to an increased variety of genomes in the population, an effect that is generally beneficial as we will soon see.

When a new cell in your body arises it may contain some errors in the genetic code where the code was not copied correctly. This can be a single nucleotide that is wrong, or it can be a series of nucleotides. This is known as a mutation. If the mutation occurs in a sperm or egg cell then this mutation may be passed on to a child. Contrary to popular belief, most mutations are not harmful. They have little noticeable effect. Occasionally you will find one that is beneficial to your chances of leaving children behind. This mutation may then be perpetuated by reproduction.

NATURAL SELECTION

Natural selection is the process by which life on earth selects against harmful genes, and for beneficial genes. This is not a cognitive selection, rather it is an intrinsic property of life.

If an organism has a deleterious mutation, it is more likely to die before it can pass on its genes. If this is the case then the deleterious mutation dies with it, and is selected out of the gene pool. On the other hand, a beneficial gene will cause its host organism to have better success at reproducing. Through this, the gene will thrive in the population, and there may be an evolutionary trend in the population towards the specific characteristic coded by that gene.

It is noteworthy that natural selection selects only for genes that make an organism more likely to procreate. Though intelligence may seem great, there is no reason that natural selection would select for this trait unless it had some reproductive advantage.

A common misconception about natural selection is that it is goal oriented. People think that there is a pinnacle to evolution. Some even go as far as to say that humans are at the pinnacle of evolution. This is simply a fallacy. Natural selection has no goal. It simply selects for what is best in the here and now. Evolutionary trends are dictated through long-term environmental conditions and other selective pressures, not a preordained goal.

EXAPTATIONS.

The processes of evolution do not build new biological machines altogether, rather, they take what is already there and modify. An exaptation is a shift in the function of a trait. Though the trait may have originally evolved for one reason, it now serves an entirely different purpose. For instance, one example of this is the evolution of feathers in birds. Currently, the most widely accepted theory on feather evolution is that they evolved for thermoregulation, and perhaps courting rituals. Flight came much later.

GENE FLOW AND GENETIC DRIFT!

Earlier I mentioned that aside from mutations, recombination and natural selection, gene flow and genetic drift can also affect the genetic makeup of a population.

Gene flow occurs when an individual who did not originally belong to the population enters the population. For instance, say we had been raising 10 generations of German shepherds. If we let a Doberman inside, this would be an example of gene flow. The Doberman's genes would enter the population, and quite possibly change the genetic makeup of the population.

Genetic drift is the change in the genetic makeup of a population through purely chance events. This could allow a bad gene to linger in the gene pool longer than it should. For instance, say one bad gene has been paired up with an enormous amount of good genes. This happens generation to generation. The bad gene will affect more and more organisms. This changes the genetic makeup of the population, causing the population to evolve.

THE PAINFULLY OBVIOUS CONCLUSION

Hopefully by now you have a basic understanding of what evolution is and understand the basic mechanisms underlying it. Now that we know what it is, lets see if we can come to the same conclusion as Darwin through basic facts.

In hindsight, the theory of evolution seems so painfully obvious to me that I'm absolutely shocked that the theory was not popularized earlier. Four fairly obvious observations is all it should take to formulate an idea similar to Darwin's. In fact, it should force us to come to the same idea as Darwin. The four observations:

1.) There are qualities that an organism acquires from its parents. From this we can infer that there is a unit of inheritance.

2.) The unit of inheritance is not a perfect replicator. Albeit few, some copying errors to happen from time to time.

3.) Organisms compete amongst each other for resources to live.

4.) There are a limited amount of resources available to an organism.

The first two points account for the variation in the population, the last two points account for survival of the fittest. I do not think I can extrapolate any other conclusion from that.

SPECIATION

Speciation is the method by which new biological species arise. When a parent population becomes significantly different enough from a child population to where members of those two populations could not mate with each other then speciation has occurred. This is a cumulative effect of smaller changes. Each species can now diverge on its own line. They may end up being drastically different from each other at some point in the future. Speciation has been observed.

EVIDENCE OF EVOLUTION

The best evidence that all things alive are related is our genetic code, in my opinion. The fact that everything that has thus far been examined shares the same genetic code is a very strong indicator that we all share a common ancestor. There are sixty-four possible codons an organism can make. Those 64 codons are mapped to 20 amino acids. The chance that one organism would share this same mapping with another organism without some form of common ancestry is infinitesimally small. The mathematical calculations are fairly simple. To see the chance of two subsequent events happening you multiply the probability of each event happening. The fact that one codon is mapped to the correct amino acid has a one in twenty chance to happen at random. Since we can have 64 amino acids, we need to raise that to the 64th power. What we get is remarkable: the chance that two organisms would randomly share their genetic code is on the order of 1 in 10^83, or one in 100 sexvigintillion, or about one in a million million million million million million million million million million million million million million million million million million million million million million million million. Quite literally, that many millions.

More direct evidence comes from other things as well. For instance, with modern technology we can compare our DNAs with that of other animals, and compare similarities and differences. Again, the similarities are just too striking to have happened by chance. We have a fairly rich history of life on earth through the fossil record. While it is by no means complete, it still stands in support of evolution. The geographical distribution we see of animals reflects exactly what we would expect to see had they evolved. All the detailed evidence for evolution is just too broad to get into here, however there is so much that the theory is undeniable.