This refers to the gradual development of complex organisms from simpler ancestral types over a long period of time. This is caused by changes in the populations resulting from inherited variations in individuals in successive generation.
Evolution begins with the production of new species which gradually differ more and more from each other until new genera, families, classes, have evolved.
Origin of life:
The exact origin of life is not known. How ever some theories have been put forward to show the origin of life which include;
- Steady state theory: this suggests that life has no origin and it has been existence.
- Spontaneous generation: This indicates that life arose from non living matter on numerous occasions.
- Special creation: this indicates that life was created by a supernatural being at a particular time.
- Cosmozaon theory: this suggests that life arrived on this planet from else where.
- Biochemical evolution: Most accepted theory by scientists. It suggests that life arose from according to biochemical and physical laws which lead to formation of certain macromolecules which make up DNA and body cells.
Evolution theory explains that the different species of organisms existing today arose from common ancestors which were originally primitive but gradually under went changes along different evolutionary lines in different environments in order to survive in those environments. The trend of evolution there fore, is gradual change from primitive form of life to advance d form of life.
Theories of evolution/mechanism of evolution
- Lamarck’ theory of evolution/Lamarckism: based on acquired characters through use and disuse.
This theory was put forward by a French biologist Jean baptiste Larmarck in 1809. his theory resolves itself into 3 factors namely;
a) influence of the environment
b) Use and disuse
c) Inheritance of acquired characters
Based on the above factors, he suggested that; when an organism develops a need for a particular structure in a given environment, this will induce its appearance and there fore the structure will develop to carry out the need in that environment. This idea was based on the observation that the structures which are subjected to constant use become well developed and those which are not used tend to degenerate hence the theory of Use and disuse
i) Ancient giraffes were those living today. Lamarck urged that as the number of giraffes increased, there was shortage of food in form of grass, herbs and leaves from very short shrubs. This compelled them to stretch their necks so as to reach for leaves on higher branches of tall trees. The result was elongation of the necks.
The off springs of these giraffes inherited the longer necks, stretched further and the process was repeated until the present long necks were developed.
ii) exercise and training can lead to the development of muscles of a heavy weight lifter, since he suggested that these beneficial traits acquired in an individual’s life can be passed onto the off springs, hence evolutionary change can be achieved via transmission of acquired characteristics, This implies that a heavy weight lifter who has acquired big arm muscles produces children with big arm muscles.
However this was proved totally wrong by genetic evidence that acquired characters can be inherited. This theory there fore is not scientifically accurate.
Darwin’s theory of evolution/ the base on natural selection or the theory of natural selection (Darwinism)
The first satisfactory explanation to the mechanism by which evolution takes place was proposed by Charles Darwin (1809-1882) and that was the theory of natural selection.
Natural selection is where by the well adapted organisms to changes in the environment are naturally favoured or selected for and survive while the poorly adapted organisms to changes in the environment are naturally selected against and die before reaching sexual maturity or before reproducing.
The well adapted and naturally favoured organisms which survive the changes in the environment pass on their beneficial traits/genes which made them to survive to their off springs (survival for the fittest)
And those which are less adapted will be naturally selected against and they will die off before reaching sexual maturity there fore leading to the elimination of un beneficial genes/traits from the population.