Lesson Objectives:- Natural Selection
- The Theory of Evolution
- Keys to survival
- The evolution of species
- Isolation and species
Selective pressures: Most young plants and animals do not survive because they face environmental resistance factors such as predators, parasites, drought, lack of food and temperature extremes.
Survival involves developing characteristics that help a species adapt, hide from predators and benefit reproduction. The process of specific traits favoring the survival of certain individuals is known as natural selection. Charles Darwin first presented these theories in his book "On the Origin of Species by Means of Natural Selection" in 1859.
Evolution is the modification of the gene pool of a species by natural selection over the course of generations.
Both Charles Darwin and Alfred Wallace came to these conclusions independently without the use of DNA, solely through observations and study. It was only in the 1960s that the study of genetics revealed that these theories were valid and that evolution occurs through natural selection.
Fitness involves the traits of an organism that help it survive and reproduce.
Examples include coping with temperature changes, obtaining food, escaping predators, finding mates and migration. Does a trait help an organism survive and reproduce? If it does, then it will be maintained through natural selection. When change occurs, populations adapt, migrate or go extinct.
There are four keys to the survival of any species. They are geographical distribution, specialization to a habitat or food supply, genetic variation within the gene pool, and the reproductive rate relative to the environmental change.
For example, the housefly does not require any special habitat and can reproduce in practically any environment. It is not a vulnerable population. The condor, by contrast, requires a large roaming range, has specific prey and food requirements and does not have much genetic diversity. It would be severely impacted if its environment were destroyed or damaged.
Species have always been adapting to changing environmental conditions. Today, there are 8.7 million known species of plants, animals and microbes. There are millions that are still unknown.
Mutations and adaptations from two species interbreeding has resulted in new species. For example, with the fox, populations have changed dramatically based on location as the species has adapted to different environments. The arctic fox has developed heavy fur and a short tail and light color to blend into the background in the north, while the southern gray fox has thin fur, long tail and a dark color, adapting to the warmer climate.
The isolation of species on different land masses has led to distinct variations and development. Drifting continents and isolation have created species in areas that are unlike any other. A good example of this includes the many distinct species in Australia and Indonesia, both areas of the world that were relatively isolated from the rest of the world for a long time.