BIOLOGY FORM FOUR TOPIC 4: EVOLUTION
Concept of Organic Evolution
Lamarck’s theory of Evolution
State lamarck’s theory of evolution
Darwin was not the only person to develop a theory of evolution. Jean-Baptiste Lamarck was a French scientist who developed an alternative theory at the beginning of the 19th century. His theory centred on two ideas:
- the law of use and disuse
- the law of inheritance of acquired characteristics
His theory stipulated that a characteristic which is used more and more by an organism becomes bigger and stronger. One that is not used disappears eventually. Any characteristic of an organism that is improved through use is passed to its offspring.
Lamarck’s Observations and Deductions
Explain lamarck’s observations and deductions
Jean Baptiste Lamarck was a French naturalist. Lamarck formulated a theory on evolution after studying botany and the fossils of marine invertebrates.
He used the law of use and disuse which explains that organism enhanced certain abilities by exercising them and lost other abilities through disuse example the ancestors of the present day long necked giraffe. These early giraffes fed on short plants when the short plants became scarce the giraffe had to stretch their necks to feed on taller plants. Thus their necks became longer. The longer necks were passed onto their offspring hence after a long time giraffe developed the long necks they have today.
His theory was based on inheritance of acquired characteristics the offspring then adapt further, advancing evolution of the species.
Merits and Demerits of Lamarck’s Theory of Evolution
The Merits of Lamarck’s Theory of Evolution include:
- Lamarck theory lead to further studies on evolution of species
- It gave rise to discovery of genes and genetics which is now widely used in many fields of biology
- Upon rejection of his theory Lamarck decided to study about invertebrates which made great contribution in development of Zoology
Darwin’s Theory of Evolution
State Darwin’s theory of evolution
Charles Robert Darwin (1809 – 1882) was an English naturalist. He based his theory on observation made during a five-year geographical study.
Darwin’s main observations were:
- Every generation of organisms have more off springs than parents. However, the number of adult organisms remains generally stable from generation to generation. Therefore is a struggle for existence that causes many off spring to die before becoming adults
- There are many variations in a species. Variations are passed from parents to their off spring. Advantageous variations enable survival in the environment organism with disadvantageous variation due. This is called survival of the fittest.
- Off springs with favourable variations grow into adults and reproduce therefore favourable variations accumulated in the species; enabling adaptation to the environment, this gives rise to new specie.
- A change in the environmental conditions favours other characteristics of the organisms. The effect of these changes on the organisms is that other features become more prominent than before resulting in evolution.
Merits of Darwin’s theory
- The theory enabled scientists to carry further studies, leading to new discoveries that suggest the origin of life
- Helped scientists to understand about drug resistance and evolution of germs like bacteria and viruses leading to new strains
- Enable further research to find cure or vaccines of germs, bacteria and viruses
Shortcoming of Darwin’s Theory:He failed to explain how variations in populations arose and were maintained from one generation to the next.
Evidences and application of Organic Evolution in the Real Life Situation
Investigate evidences and application of organic evolution in the real life situation
Scientists can prove that evolution has taken place by various methods. Some of these methods are
- Comparative anatomy:Comparative anatomy is the study of biological structures in different organisms. The scientists look at structures that are similar in different organisms or species. Example limbs of vertebrates such as human beings, goats and wings of birds are used for different purposes but they have a basic design structure, this is known as homologous structure.Example fore limbs of humans are for manipulation, fore limbs of birds (wings) are for flight and fore limbs of a goat are for walking; this shows that all these animals are from common ancestors. Analogous structures are the ones, which look different, but they perform similar functions e.g. insect, birds and bats all have wings used for flight but they have different structural organization.
- Fossil records:Fossils are remains of organisms that lived in the past preserved naturally in rocks or on ice. The study of fossils is known as paleontology when fossils are dated scientists can estimate the age of that organism. Method used by scientists to know the age of fossils is carbon dating using isotope of Carbon 14.
- Embryology:In comparative embryology embryos of different vertebrates at early stages are compared and they are seen to have resemblances. Species that show similar embryonic development are assumed to be closely related although the adult may be quite different
- Natural Selection in Action:Nature led to the selection of a genetic combination that resulted in a more frequent melanic variety compared to the non-melanic variety. Before the industrial revolution in Europe the white variety of moth was more prevalent. Industrialization in Europe in the 18th Century polluted the environment, burning of coal released a lot of soot and smoke. These pollutants coated tree trunks, killing the lichens that grew on the tree trunks. The colour of the tree trunks became black; this camouflaged the dark melanin form of the peppered moth. The predators of the moth did not feed on many dark moths because they were not very visible.
- Evidence from vestigial organs:These are structures, which have been greatly reduced and ceased to be functional. Presence of vestigial organs is an indication that they existed in ancestral forms but as a result of evolution such structures have been so much reduced to the extent of loosing or greatly changing their original function. Examples of vestigial structures are wings of flightless birds such as ostriches and penguins.