Biological evolution is defined as any genetic change in a population that is inherited over several, successive generations. (R.Bailey, 2014) The changes accumulate and over time a new species is created. One of the basic mechanisms of evolution is Natural Selection. Natural Selection is random genetic variation occurring within an organisms DNA and the beneficial mutations being preserved because they aid survival. (C.Darwin, 1859) Two notable scientists associated with the theory of evolution include Charles Darwin and Jean-Baptiste Lamarck.
Charles Darwin contributed majorly to the evolutionary theory and was the first to consider the concept of natural selection. The evolutionary theory states that evolutionary change comes through the production of genetic variation in each generation and survival of individuals with different combinations of these characters. Individuals with characteristics which increase their probability of survival will have more opportunities to reproduce and their offspring will also benefit from the heritable, advantageous characteristic. So over time these variants will spread through the population. (S.Montgomery, 2009)
A prime example of natural selection is the development of antibiotic resistance in bacteria. In a given population of bacteria, there may be some that carry a short segment of DNA coding for a protein which is resistant to a given antibiotic. If that population now encounters that antibiotic, there is a major selective pressure - those bacteria that do not have the antibiotic resistance gene will die. The only ones that will survive will be the ones carrying that gene. Therefore, those remaining antibiotic resistant specimens will be able to reproduce, passing along the antibiotic resistance gene to their offspring. Over a very short time, the dominant bacteria in the population will be the ones resistant to the antibiotic.
In comparison, Jean-Baptiste Lamarck proposed that the environment and natural processes gave rise to change. His theory stated that characteristics acquired in an organism’s life time and would be inherited by its offspring. (http://en.wikipedia.org/wiki/Lamarckism) When environments change, organisms have to change their behaviour to survive. For example, if a giraffe stretched its neck for leaves and exercised its neck muscles more, it would grow a longer neck and its offspring would inherit the longer neck. Each generation, the Giraffe’s neck stretched more and more. Meanwhile muscles and body parts that organisms stopped using would shrink.
However, in Lamarck’s theory, there are clearly a number of fundamental flaws. For example, if a person loses a limb through injury and has a child later in life, is the child born without that same limb? Human cannot alter their genetic structure (genotype) and the gametes given to offspring are chosen at random.
-Species change according to habitat
-Different characteristics within a populace Darwin Lamarck