Evolution
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Evolution is defined as the change in the inherited traits of a species and the emergence of new species from old species over time.
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History of Evolution
Although there was some scientific discussion about evolution or similar before this, Charles Darwin (1809-1882) had formulated his idea of natural selection in 1938 and continued his research without submitting any of his work for publication. In 1858, Alfred Russel Wallace (1823 - 1913) sent Darwin a similar theory which he had formulated independently of Darwin's research. They both submitted their theories to the Linnean Society of London in 1958. The following year, when Darwin published his On the Origin of Species (November 1959), he laid out evidence for the theory of natural selection and the occurrence of evolution gained widespread acceptance among the scientific community.
Evidence for Evolution
Comparative Biochemistry
Comparative biochemistry allows us to compare the DNA, ATP and protein structures of organisms. By comparing the similarities or differences between organisms, scientists are able to evaluate how closely related they are. The greater the similarity in protein structure, and the smaller the difference is in their DNA structure, the closer the relation between organisms.
Natural Selection
Darwin and Wallace proposed a mechanism by which evolution occurs. This key mechanism is known as natural selection.
The process of natural selection has four components:
- Variation - individual members of a species can exhibit different traits from one another.
- Inheritance - offspring inherit traits from their parents.
- High rate of population growth - as more offspring are produced than the local environment can support, there is a battle for resources and a high mortality rate.
- Differential reproduction - some individuals will have variations which make them better able to survive in their environment. These individuals will pass on more offspring to the next generation, compared with individuals less likely to survive and reproduce.
If these four conditions are met, two observable conclusions are formed:
- The individual members of a species who survive to reproduce will tend to pass on to their offspring the trait which enabled them to survive, thus, given time, this trait will become the norm.
- As a result of natural selections, populations will eventually become so different that they won't interbreed, instead splitting into new species.
Evidence for Natural Selection
Natural selection can be observed in the world today. An example of natural selection is the development of antibiotic resistance in microorganisms. Populations of bacteria contain variations in genetic material due to mutations. When exposed to antibiotic treatment, most bacteria die quickly. However, some may survive the course of antibiotics as a result of specific mutations that they carry, making them less susceptible to the antibiotic. If enough of these bacteria survive treatment by antibiotics, and the rest of non-resistant population are eliminated, this mutation will be passed along to the next generation of bacteria. Given enough time, and exposure to antibiotics, a population of antibiotic resistant bacteria will emerge. The elimination of non-resistant bacteria, and the reproduction of bacteria carrying the resistant mutation is evidence of natural selection.
Relevant Exam Questions
2009 HL, Section C, Question 10 (c) (part of question with total of 60 marks).
- (iii) What is the significance of inherited variation in the evolution of species?
- (iv) State two types of evidence used to support the theory of evolution.
