Natural selection – continued
WELL, HELLO again, students! Can you believe that another week has passed? Not only does time pass quickly when you are having fun, it also passes quickly when exams are near!
Last week, in our lesson on natural selection, we looked at the role that variation plays in helping natural selection to take place. This week, we will continue to look at the process. We cannot do this without sharing a little bit of scientific history, the history surrounding the work of Charles Darwin.
WHO WAS CHARLES DARWIN?
Charles Darwin was a British naturalist and he was the first scientist to collect evidence to support the theory of evolution. In 1831, he left England to travel around the world in his ship, the HMS Beagle. He visited many places where he studied their wildlife. He brought back to England many specimens of organisms that he had seen and used information gathered from these to write his book, The Origin of Species. In it, he wrote his thoughts on how evolution might have taken place; he called this The Theory of Natural Selection. Darwin developed his theory of evolution by natural selection using these four important observations:
1. All organisms produce more offspring than survive to adulthood.
2. Populations remain more or less constant in numbers.
3. Members of the same species show variation in characteristics.
4. Some characteristics are inherited and so are passed on to the next generation.
THE GALAPAGOS ISLANDS
This is a group of islands off the coast of South America. While there, Darwin studied 13 different varieties of finches (birds). He suggested that they could have developed from birds that originated from the mainland. In his observations, he noted that the birds had different beaks for different diets (Figure 1). Darwin suggested that these birds all originated from seed-eating finches that had come from the mainland, but that there might not have been enough seeds to allow all the birds to survive. Finches which had slightly different beaks would have been able to eat other types of food and, in so doing, would have been able to survive and reproduce, passing these adaptations on to their offspring. This, he said, would be an example of natural selection.
Now, use the Internet or go to the library and read up on the work of Darwin. It will help to clear up some of the misconceptions that may be clouding your minds!
OTHER EXAMPLES OF NATURAL SELECTION AT WORK
Bacterial resistance This one is very relevant to our Jamaican society because we have a fondness for pills. We tend to believe that a pill is the cure for every bad feeling or illness under the sun. If you do not believe this, go and ask your school nurse about the number of requests that she gets for pills. So, if we are sick with a viral disease, we request antibiotics from the doctor who, in many instances, provides it. Additionally, when we do have a bacterial infection and the doctor prescribes the antibiotic and tells us to take all of it, we do not do so; we stop as soon as we begin to feel better! This has lead to the overuse of antibiotics. What happens because of this?
Mutations in the members of the bacteria population can lead to some of them having traits that allow them to be immune to the antibiotic. Some of these bacteria will begin to develop resistance to the antibiotic. Bacteria reproduce rapidly, hence, in a short time, multiple generations can develop and these will have the acquired resistance to the antibiotic. Very soon, that antibiotic can no longer be prescribed for any illness caused by the bacterium. The MRSA (methicillin-resistant staphyloccus aureus) bacterium falls into this group; it has now developed a resistance to penicillin because of this.
THE PEPPERED MOTH – BISTON BETULARIA
There are two types of peppered moths and it is thought that these two types developed due to changes in the environment.
THE TWO TYPES ARE:
1. A pale, speckled form 2. A dark form The moths which feed at nights and rest in the day are preyed on by birds.
During the age of industralisation, the nature
of the trunks of the trees changed. The lichen that grew on the trunks of the trees died and the trunks became dark from industrial pollution. It was noticed that the population of dark moths had increased drastically in the industralised areas. Previously, only very few of these were seen.
Today, both dark and speckled moths are found in the British Isles, both types occurring where the chances of their being preyed on are less, i.e., the pale form in the areas where there is still lichen on the trunks of the trees, hence making them less visible to birds, and the dark form in the areas where the trunks are dark from soot, making the moths less visible to the birds. See you next week as we continue.