10F ~ Science ~ Mr. Coates
How Theories of Evolution Have Changed Over Time
There are many theories that strive to explain the genetic evolution of organisms. Over time, as new information and data becomes available through research, the scientific theories change. The new theories are often more plausible, making up for the previous flaws, furthermore replacing the prior theories and being accepted by the scientific community. This is known as a paradigm shift. Two pioneering theories and an example of paradigm shift are the proposed concepts of Jean-Baptiste Lamarck, and the latter notion of Charles Darwin. Both theories will be compared to explain the evolution of methicillin-resistant Staphylococcus bacteria.
Jean-Baptiste Lamarck (1744-1829), was a retired French soldier who, after serious injury, became a famous zoologist and botanist. After spending years undertaking research at the Jardin des Plantes, a botanical garden and centre for medical education and biological research, in 1801 Lamarck published details of his evolutionary theories. In his publishing’s, he described three biological laws. The first law suggested that environmental alterations cause changes in the needs of organisms living in that environment, additionally causing variations in organ and body development. This then led to the second law. Altered behaviour due to the impact of environmental change leads to greater or lesser use of a body part or organ; greater use would cause the structure to increase in size over several generations, whereas disuse would cause it to shrink (refer to Figure 1). The third law was that these acquired traits would be inherited by the organism’s offspring and future generations.
Figure 1 – Lamarck’s Giraffes (https://benchprep.com/blog/ap-biology-evolution-part-2/ )
Charles Robert Darwin (1809-1882), studied at Edinburgh University, Cambridge, England, under J. S. Henslow, professor of botany. Upon Darwin’s graduation as a geologist, he was recommended by Professor Henslow to assume the post of naturalist in H.M.S. Beagle, on a five-year survey voyage around the world, from 1831 to 1836 (refer to Figure 2).
Figure 2 – Darwin’s voyage
During this voyage, he observed the variety of living organisms and their variation between different environments. These observations formed his theory of evolution by natural selection. The voyage explored the coastal areas of Australia, Van Diemen's Land (now Tasmania), and the Galapagos islands, which Darwin was quite interested by. The geographical isolation of the foreign organisms gave Darwin valuable evidence of evolution; and the Aboriginals provided support for his theory of natural selection. Darwin described natural selection as ‘modification by descent’ which is the mechanism of change both within species and leading to the formation of new species over time. He explained two main factors involved in the process: variation and speciation. Darwin discerned that variation in phenotypes was a crucial factor of natural selection. An example to describe this process was the peppered moth (refer to Figure 3) studied by Henry Bernard Kettlewell.
Figure 3 – Peppered moths
It was noted that there were two colour variations in the moths: light and dark. In some locations, pollution contributed to the colouration of tree trunks where the moths rested. This meant that the light coloured moths were more prone to being attacked by predators on the darkened trees and the dark coloured moths were more susceptible to enemies on the light trees. This meant that the population of dark moths outnumbered that of the light moths in the darkened environment as the light moths were killed before they were able to reproduce; vice versa for…