1. Adaptive maturation of the immune response. Virtually every aware person is familiar with the effects of the immune response, from immunizations to allergies. During the immune response, a remarkable and rapid adaptive evolution of antibody molecules occurs. During this adaptive evolution, the genes coding for the antibody secreted in response to a specific antigen–like ragweed–accumulate successive mutations which progressively increase the affinity for antigen. That is, the initial exposure may produce no symptoms; but successive exposures result in increasing runny nose, sneezing, and watering eyes.
When an organism is exposed to an antigen and mounts an immune response, a complex sequence of events ensues which binds antigen to immature antibody secreting B cells. Those B cells, whose antigen receptors, each with the same specificity as the antibody it will later secrete, form the best match to the invading antigen; and they proliferate most rapidly. This leads to a selected antibody accumulation which better matches the antigen than any other potential antibody. Prior to the antigen exposure, the protein antibody was not present in its specific chemical form. After several exposures, even more specificity and quantity of the antibody is produced and more quickly than the time before. If the antigen is a hormone, the peptides involved may bind to its receptor and antagonize, agonize, modulate, or simulate the hormone. This process is crucial in seeking candidate drugs for experimentation in human disease. The process of adaptive maturation of the immune response is a clear demonstration of the type of biochemical processes that are the underpinnings of evolutionary selection. A striking example is found in the development of bacterial resistance to anti-microbial agents.
2. Bacterial resistance to antibiotics is related to easy genetic selection in many bacteria. Extended spectrum ß lactamases, are enzymes that make Escherichia Coli–among others–resistant to most antibiotics. For example, TEM1 makes E. Coli resistant to Ampicillin causing at least one-half of the urinary tract infections around the world to be resistant to that antibiotic. By changing a single amino acid in that enzyme, the ß lactamase can change the bacteria from susceptible to resistant to the drug cephtazamine in a matter of days. The powerful antibiotic, Vancomycin, requires the annealing of multiple gene products into a single structure or cluster. It took forty years for the first resistant strain to occur in enterococci. This is genetic selection that occurs within the lifetime of most of us. Similarly, soil bacteria develop the ability to survive on, then thrive on, and finally become obligate to, formerly toxic environments. This adaptability is such that the soil bacteria can rapidly evolve to cope with another new change in its environment frequently, as it must for the species to survive and persist. In many instances, the evolutionary process is clearly understood. Consider the precision of one selected article by Beckler, D.R., Elwasila, S., Ghobrial,G., Valentine, J.F., and Naser, S.A., from the Department of Molecular Biology and Microbiology, Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Correlation between rpoB Gene Mutation in Mycobacterium Avium Subspecies Paratuberculosis and Clinical Rifabutin and Rifampicin Resistance for Treatment of Crohn’s Disease, World Journal of Gastroenterology, 14: (17) 2723-2730, May, 2008. The researchers tested the two named drugs against the mycobacterium over time and recorded an increase in the minimum inhibitory concentration of the drug required to eradicate the bacteria by 30 fold. They traced the resistance to a mutation: By molecular biological methods, the mutation was identified as a small nucleotide substitution between nucleotides 1363 and 1443. The authors were able to refine that locus to a novel rpoB mutation C1367T which caused an amino acid change Threonine 456 to Ile 56 in the drug’s binding site. No other significant mutations were found.
3. Originally, the Hawthorne maggot fly (Rhagoletis pomonella) fed only on that plant. About 100 years ago, it underwent a mutation–with six out of thirteen alozyme loci becoming different–that caused it to adapt to feed on apples; and shortly thereafter, it became a major threat to apple farming in the northern United States. Apple flies take less time to mature. There is little evidence of interbreeding—a documented 4-6% hybridization rate—which is an example of a species undergoing speciation during the lifetime of individual people.
4. Yaws is a childhood skin infection whose existence is clearly dated from ancient times and is caused by a bacterium, Treponema pallidum which is transferred person-to-person by skin contact. In 1492 Columbus and his crews encountered Amerindians who were known to have yaws and carried the infection back to Europe. In Europe conditions known to foster the emergence and propagation of sexually transmitted diseases existed in near perfect form—over-crowding, high level of promiscuity in conditions of filth and anonymity, and a relatively high level of mobility.
Syphilis–also caused by Treponema pallidum–was almost unknown until the fifteenth century A.D. In the bacterial stew pot of medieval Europe, the previously rare occurrence of sexual transmission of Treponema pallidum reached a critical mass of frequent and multiple partner sexual intercourse, and the bacteria mutated into a dominant and virulent form. Instead of being transmitted as the benign form yaws, it emerged as syphilis which was first recorded during the Franco/Italian war beginning in 1495, an infection that reached epidemic proportions. Spanish sailors regularly returned to the Americas after their first visit. During the fifteenth century, Amerindian populations were decimated by the sexually transmitted disease.
5. In the savanna country of eastern and southern Africa, Apis mellifera scatellata bees developed into a highly defensive and aggressive bee, commonly known as African Killer Bees. They were intentionally introduced into Brazil in 1956; by 1990 they had advanced northward and invaded Sinaloa, Mexico producing large numbers of pure and also feral and hybrid colonies. In 1994 Africanized bees arrived in Blythe, California. By 1996 there were 21 established colonies found in the Imperial Valley. These insects are true killers of humans, livestock, and other bees. On the other hand, European honey bees are ordinarily quite docile, benign, and useful because they produce large quantities of honey for storage.
The process of Africanization is a straightforward example of evolution in action. The African bees have several characteristics that allow them to become dominant over European honey bees. They are extremely defensive and are more easily agitated. They very rapidly swarm to attack a presumed threat. They are more aggressive by nature and attack and take over honey bee hives. The African bees produce far more drones, and these drones rapidly invade honey bee hives and drive out the queen bee’s protectors and drones and then dominate the breeding process producing hybrids that become full blown African bees in a matter of only a few generations. The Africanized queens produce more offspring more rapidly—with gestation periods of three days as opposed to the seven days required for honey bees. Although Africanized bees produce much more honey than honey bees, they do not store it, but instead, they use the honey for rapid colony reproduction. The Africanized bees are more efficient foragers and fly faster, thereby bringing more pollen back to the hive to use as fuel for the manufacture of honey. When the hives become too large, or the weather cools to the point of intolerability, queens and their attendants move on, in an inexorable march in all directions repeating their predations, rapid procreation, and evolution.
6. Nylon eating bacteria: A Pseudomonas aeruginosa, strain POA, now exists which required new enzymes to digest a material efficiently that never existed until the modern age. The gene, however, did exist and served other functions; but when nylon became available, a simple gene frame shift occurred that allowed the bacteria to consume and digest nylon, a kind of plastic. The bacteria responded by being able to reproduce faster and more plentifully on a diet of nothing but nylon, a fiber produced only by man. The newly evolved enzyme’s crystal structure has been studied with high resolution x-ray which revealed that the amino acid replacements in the catalytic cleft of a pre-existing esterase (an enzyme) with a ß lactamase fold resulted in the evolutionary change.
7. Perhaps the most obvious, evident, and factual demonstration of natural selection resulting in a species change is found in the human immune virus—HIV. The virus is a weak construction of two RNA strands which are strung with genes, and the strands are held together by a sugar-based encapsulation. When HIV enters a cell it uses cellular parts to transform to DNA; and the process is made possible by an enzyme, reverse transcriptase. Using that enzyme, HIV produces some 10 billion new viruses a day. Mutational processes in cells ordinarily have mutations so infrequently that only three or four occur in a person’s life time, and most of those come to naught. HIV reverse transcriptase is highly inaccurate and capricious. It produces some 10,000 mutations every day. Because of this demonstrable capacity to mutate, anti-HIV medications become ineffective very quickly.
Scientists and drug companies rush to produce ever newer medications to keep up with the demands caused by this clear example of natural selection. It is a huge problem world-wide of which physicians are well aware, and even third-world victims of HIV infections become rather quickly aware. For example, the highly touted and relatively inexpensive drug, Nevirapine, has been given as a single daily dose to tens of thousands of infected pregnant African women to prevent mother-to-fetus transmission of HIV. Initially, it was remarkably effective. However, now–most of time–drug resistance occurs rendering the treatment useless. Effective multiple drug regimens are available with a much lower rate of developing resistance, but these regimens are out of reach for individual Africans and even their countries because of the great cost.
8. The elucidation of the rapid evolution of the enzyme ß galactosidase is a particularly good example of the evolution of protein differentiation. Evolved ß galactosidase has been shown repeatedly to code for a protein capable of evolving ß galactosidase activity. The wild type protein appears to have some activity toward an analogue of lactose, but very little activity toward lactose itself. Mutations which result in the capacity to catalyze lactose breakdown include strains that grow rapidly on lactose, but not on the disaccharide lactulose. Other strains grow slowly on lactose but somewhat more rapidly on lactulose and have a wider range of activity in general. The wild, unmutated gene does not allow galactose-arabinoside to be used as a sole carbon source, but both types of mutated bacteria permit limited ability to use the new sugar source. Double mutants–two different sites–are significantly more capable of growing on galactose-arabinoside than the wild bacteria or either of the two mutants alone. continued…