Evolution is the process by which speciation (the creation of species) occurs. Each type of organism is a species, divided into these groupings by characteristics such as anatomy and physiology. Evolution also refers to the adaptations that occur in organisms, such as treatment resistance in pathogens. The scientific theory of evolution is based on more than 150 years of research and observation, most notably by British scientist Charles Darwin, who recognized adaptational mutations in species isolated on the Galapagos Islands in the 1800s.
In Natural Selection
Evolution is a relatively slow process, requiring reproduction events and generations in which to unfold. The process of evolution is the mechanism by which natural selection occurs. Natural selection is also known as survival of the fittest, meaning reproduction fitness. The organisms within a population who are best adapted to their environment have a better chance of reproducing and passing along their genes, including any mutation that may be present in the genomes. Over several generations, the allele frequency within the population can be altered by the elimination of some features due to a lack of breeding by individuals carrying particular alleles that do not convey survival adaptations, or sometimes it is without survival association, the alleles just disappear due to a lack of breeding within a population (extinction). This allelic shift then results in a new population norm.
Hereditary genetic mutations are alterations in the DNA sequence, called the genotype. The DNA is made up of genes, which encode all proteins required by the organism, including anatomical features and characteristics called the phenotype. Variations within a species or population are due to alleles, differing copies of the same gene resulting in different phenotypes.
When mutations occur, they alter the genotype, but not always the phenotype. Some mutations are silent, in that they do not result in any measurable change in the organism- the protein is the same. Some mutations do result in an altered protein, but not an altered effect (no phenotypic change). Other mutations result in a phenotypic change, which then can alter reproduction fitness and the allele frequency in the population. Over time, this change may or may not become the norm.
Once a phenotypic change becomes a part of the population, the individuals now differ from the original population, and may be a new species depending on the overall impact of the alteration. Over time, with breeding and passing on the new characteristics, the population of the new species grows.
Sometimes the mutation disappears, sometimes it sticks around as a minor allele (often without a phenotypic change), other times it becomes the norm. When a mutation becomes the norm, it has been a part of evolution.
This process has been observed several times in the past few decades. Here are just a two examples:
1. A population of lizards was isolated on an island. After a few decades, researchers revisited the lizard population and found that the population on the island genetically derived from the original lizards had a number of individuals with a stomach pouch not known in the species. Due to their new environment, those with a mutation for a particular digestive function reproduced more efficiently and passed on traits that resulted in a new, mutated population.
2. One of the most famous examples of adaptation is that of the peppered moth. Prior to the Industrial Revolution, the peppered moth was most often light in color, with slight dark variations. After the presence of coal dust began to settle, the white moths were susceptible to predators, leaving behind the dark moths to reproduce. Over time, peppered moths became dark in color because the ones who were camouflaged were the ones who reproduced, passing on their genes.
In Pathogen Adaptability
Pathogens are much more simple organisms and evolve at a much faster rate. They are also better known as strains, rather than species. Mutations occur at a much higher rate in these organisms, because of a lack of fidelity in the polymerase that replicates the genome. This is a survival mechanism, allowing the pathogen to mutate and avoid immune reactions by the host.
1. The envelope proteins of HIV mutate over the course of infection, resulting in the evolution of the virus within a single individual (the presence of a different strain at the time of infection and time of death). This also makes it difficult to vaccinate for and treat the infection.
2. The influenza virus mutates each season, resulting in a new vaccine developed for the particular strain. By evolving faster than the human immune system, the virus ensures its ability to survive in the human population another season. The virus is also becoming more common in a drug-resistant form, meaning that it is evolving to avoid anti-viral therapies flu treatments that would kill it.
3. Bacteria have been found to share genes, conveying the ability to resist particular drugs and treatments. MRSA is a strain of Staphylococcus resistant to the antibiotic methicillin. Exchange between other strains that are resistant to other antibiotics has resulted in double-resistant mutants called VMRSA ( vancomycin resistant MRSA ). The bacteria have evolved in order to survive, and it has done this by accumulating mutations that allow it to be resistant to antibiotics.
