Mark Ridley (zoologist) - Scientific Contribution

Scientific Contribution

Natural Selection and genes

“The genetic variety produced by sexual reproduction offers many possibilities for how a population of organisms might change over time” (Uuniversity of Wyoming, 2005). Natural selection is a key entity of deciding who the winning mate will be. Traits associated with reproduction evolve playing an essential role in reproductive isolation. Ridley speaks of the courtship methods of various animals, “Songbirds sing, frogs croak, fruit flies dance and throw up. The reason is probably what Darwin called female choice - females tend to breed with the males who sing, and who sing loudest and longest” (Ridley, 2000). Ridley makes a contribution to this topic by attempting to answer why females chose those mates who display odd behavior. He believes the answer to this question is due to an animal’s way to assess gene quality. Genes influence behavior, which in turn influence mate choice. Natural selection chooses genes that will benefit a species helping them survive and rejects those of no further use. Ridley explains alteration of gene activity also passes down from generation to generation. The common trend of females mating with males who show odd behavior is popular due to social interaction. Social interactions in animals also trigger changes in the nervous system that also alter gene activity. There are many pieces of behavior that are influenced by genes.

Studies have shown that mutations in genes occur when reproducing, “A human being makes 200 or so copying mistakes every time he or she breeds” (Ridley, 2000). The mutations are slowed down through the mating process. According to Ridley, an individual encounters two problems when attempting to assess the gene quality of another individual. “One is how to tell which suitors have good genes, and which have bad” (Ridley, 2000). Zoologist Peter Garson studied the European wren and discovered males who spend much of their time displaying and building nests are the most successful in being chosen by the female wren. “Data collected in one of two years suggested that individual females may show a preference for males with the largest number of complete but vacant nests” (Garson, 1980). The males that are successful in nest building are at top of the selection pool allowing their genes to move forward and be passed on. This is a proactive experience in which time and effort put into nest building will give the female wren confidence in the male, which ultimately makes courtship and reproduction possible. In addition, this also eliminates mutations from occurring slowing down the gene evolving process. More so for humans then animals, Ridley says “the second problem is that, during courtship, you are accompanied by the equivalent of a smooth-talking salesperson” (Ridley, 2000). A courting male may not portray his defects to the female because his primary interest is to use his better attributes to win the challenge at hand. A reference can be made back to the odd behavior that males show. Ridley’s reasoning of odd behavior proves that it does help distinguish males from the group making them stick out to the females.

Ridley shows that courtship has been shaped during evolution by allowing a fast assessment of gene quality in a way that is not open to wrong. His study that was directed towards animals can also be considered for humans. A healthier male is more likely to win over a female than a sick over weight male. Again courtship will solidify the gene process by the decision the female makes. If she chooses the healthier more fit male then their offspring’s will most likely be healthy as well. However, if she chooses the obese male their offspring can ultimately get or become carriers of the diseases that obesity may pass on. The gene selection process will evolve more towards a negative way than a positive one for the offspring. Therefore, which mate will the female chose? She will most likely be more impressed with and want to pursue the healthier male.

Fecundity

Ridley stresses the topic of fecundity. This is a topic that most evolutionist do not talk much about. However, Ridley does a great job in introducing and developing the importance of this topic through his text and studies. According to the online medical dictionary fecundity is defined as, “the ability to have children, usually lots of them with ease” (MedicineNet, 1996). Fecundity is also when females produce more offspring than can survive. This concept is indeed universal in nature; in every species more eggs are produced than can survive on to the adult years. Darwin specifically studied the fecundity of elephants. In Darwin’s words, “The elephant is reckoned the slowest breeder of all known animals” . further research on the fecundity of elephants shows that over a female elephants main breeding life span, the females produce exactly one calf every four years. “This is a fecundity rate of 0.25 including calves of both sexes” (Patterson, 1988). This is a slow reproduction rate in elephants. Elephants are considered endangered species. The less of them that there are the harder it will be for them to mate and carry on their breed.

Mark Ridley influences the thinking of his audience by showing an approach other than what Darwin described. Darwin proved his point of low reproductive rate using the elephant as a prime example and conversely, Mark Ridley explains high reproductive rates through the Atlantic Cod. Mark Ridley explains fecundity using the Atlantic Cod, “The fecundity of females increases with size and age. A 40 inch female may lay about 3 million eggs, and a 50 inch female up to 9 million eggs in one spawning season” (Dave, 2010). Furthermore, not looking at size but at age “An average 10-year-old female cod lays about 2 million eggs in a breeding season, and large individuals may lay over 5 million” (Ridley, 2003). Out of the 2 million eggs only two survive. The two eggs that survive on average are the ones that will successfully continue to exist living. These are the eggs that will one day reproduce to continue the cycle of life. This is important in understanding evolution because the eggs that do evolve into fish and continue living are successful in reproduction. Fecundity varies depending on which animal is being considered. As seen above, it can be either a high reproductive rate or a low one. Fecundity is closely related to fitness. Fitness is a term describing the measure of reproductive success, “In evolutionary theory, fitness is a technical term, meaning the average number of offspring left by an individual relative to the number of offspring left by an average member of the population” (Ridley, 2003). “Those individuals who leave the largest number of mature offspring are the fittest” (Kimball, 2010). The production of a large number of offspring is a measure of fitness. Fitness for the Atlantic cod is measured by the number of fertilized eggs they produce because they provide little to no care for their young. Both Darwin and Ridley stress the condition of fecundity perceiving it from different perspectives. All in all, Ridley along with other evolutionists believe organisms produce more offspring than the given limited amount of resources will allow to ever survive. HIV affected by Evolution

Another point that Mark Ridley stresses is the evolution of drug resistance in HIV. “The increase in the frequency of drug-resistant HIV is almost certainly driven by natural selection” (Ridley, 2003). Reproduction, heredity, variation in individuals among the members of a population, and variation in the fitness of organisms are all characteristics that HIV possesses. A virus like HIV is prone to better and faster reproduction because it will develop the ability to resist drugs. Therefore, Ridley makes a point to prove that the HIV population when put in this type of situation evolves. Natural selection can cause adaptation or also cause a population to remain constant. Some features of HIV allow it to easily facilitate widespread resistance also due to its high mutation rate.

Another study was conducted, comparing “the rate of emergence of thymidine analogue mutations (TAMs) and major protease inhibitor mutations in adherent patients who remained on stable treatment with a thymidine analogue and/or protease inhibitor after the onset of virologic failure” (Goetz, 2006). This study proved that it was necessary to alternate the treatment plan in order to make it effective once again, “In patients kept on the same virologically regimen for a median of 6 months, there was considerable accumulation of drug resistance mutations” (Cozzi, 2007). The HIV became unaffected by a certain type of drug that was being used because it adapted to the environment it was being placed in. The virus evolved and as a result did not respond to the medicine whose purpose was to destroy the virus. Efforts are being made to find an alternative that will be more efficient; “The World Health Organization advocates a public-health approach rather than an individual-based approach to HIV treatment in order to make treatment more uniform and more available to all patients throughout the world” (Gilks, 2009). Both Ridley’s example and Goetz’s example prove that virus’s have the capability to evolve when they are exposed to the same drug over a period of time.

Mark Ridley’s example of the HIV virus portrays an example of adaptation. Ridley uses his knowledge to contribute to evolution by portraying how viruses can adapt and mutate. His study on HIV ties in perfectly will natural selection and evolution. Nearly all drugs currently used to treat this disease stop working after a period of usage and as a result cause AIDS.