prominent theories of evolution are lamarckism and darwinism and synthetic theory of evolution.
lamarch held that evolution occurs through adaptation. he argued
1. living organisms keep increasing in size upto a limit due to internal forces of life but failed to explain these forces. also evidence of dinosaurs evolving into smaller birds rejected this hypothesis.
2. growth of new organs is based on needs but today we know it is based on genetic change
3. use of organ leads to its growth and disuse makes it extinct. it is partially true as presence of human appendix useless shows.
4. all acquired characters are heritable but weismann showed only germinal traits are inherited.
also his theory was not based on solid facts and data.
Darwin explain evolution through his theory of natural selection in origin of species 1859.
1. individuals multiply in Geometric progression but population remains stable due to struggle for existence with the ecosystem.
Populations have variations.
2. only the fittest survive in this struggle and they transmit the traits to new generation.
in time this variations accumulate and species evolves.
but Darwinism did not explain negative growth of population of species.
Explainthe survival of the fittest not the arrival of the fittest and the origins of variation.
his theory of inheritance was also wrong.
too much focus on natural selection.
later modern Technology and Science was used by various scientists like dobzhansky Fischer and s wright to develop synthetic theory of evolution.
mutation genetic recombination natural selection and isolation are most important processes of microevolution.
genetic and chromosome changes create new traits.
with natural selection - directional stabilizing disruptive or
isolation - geographical behavioural or temporal changes gene frequency of population changes and
gradually it becomes a new species.
while chance events like migration or disaster can create faster evolution, hybridization creates heterogeneity and reduces pace of evolution.
1. does not explain future direction of evolution.
2. genetic recombination and chromosome number change is given more weightage.
L Frias 2010
3. Omits role of horizontal genetic transferences and the importance of viruses in host adaptation and evolution;
4. the role of non-coding DNA and non-transcriptional genes
so it is the most modern theory based on evidence but it needs to keep evolving with new molecular studies.