1.Fixed species Concept
This concept suggests that organisms remain unchanged in the past and in the future i.e. there’s no change. This kind of ideas were held by so many people like Linnean (L). Others were philosophers and religious institutions is the oldest in terms of time. The process of evolution as held up in the Bible has definite evolutionary features. These ideas were subsequently dropped by biologists because they believed that things were changing and they agreed that new organisms arose from some process of evolution from the older ones. The problem was how to explain how these changes occurred, thus the transformation theory was proposed two explain this. These theories were proposed before the time of Darwin.
2. Transformation Theory 1744 – 1729
They proposed that the transformation of qualities occurred for each individual organism within a species just like every individual changed from one form to another during its lifetime, e.g. in human beings and
individual as from infant to adult. One of the proponents of this theory was Jean Baptize Lemar (1744 – 1729) who believed that each individual is slightly because of an inner striving to adapt itself to its environment.
Furthermore, these small individual changes are passed to their offsprings. Also said that the process of chance continues in the offspring’s as they strive to adopt to their environment.
3. Darwin Concept in 1959
The work of Darwin was published in the book of origin of species, 1859. Darwin focused on variation. He proposed that
(i) Variation exist within a species
(ii) Individuals of one generation are quantitatively different form one another.
(iii) The evolution of a species as a whole results from differential rates of reproduction of the various types (traits, genotypes so that the frequency of these types is overtime. Therefore pop for the next generation will contain a higher frequency of the types that most successfully survive and reproduce under the existing environmental conditions or circumstances.
(iv) Biological evolution occurs as a result of natural selection acting on genetic diversity and this leads to changes in generation frequencies and genotype frequencies.
Kavungya answered the question on March 12, 2019 at 07:01