Natural selection theory | Darwin Theory | NMDCAT 2021

About This Video!

By the early 1840s, Darwin had worked out the major features of his theory of natural
selection as the mechanism of evolution. In 1844, Darwin wrote a long essay on the
origin of species and natural selection.
But before it could be published Alfred Wallace, a young naturalist working in the East
Indies developed a theory of natural selection essentially identical to Darwin’s. Wallace’s
paper, along with extracts from Darwin’s unpublished 1844 essay, were presented to
the Linnaean Society of London on July 1, 1858. Darwin quickly finished The Origin of
Species and published it the next year. In this book Darwin developed two main points:
1. Descent with Modification :
Darwin believed in perceived unity in life, with all organisms related through descent
from some common ancestor that lived in the remote past. In the Darwinian view, the
history of life is like a tree, with multiple branching and branching from a common
trunk all the way to the tips of the living twigs, symbolic of the current diversity of
organisms. At each fork of the evolutionary tree is an ancestor common to all lines of
evolution branching from that fork.
2. Natural Selection and Adaptation :
Darwin suggested that populations of individual species become better adapted to
their local environments through natural selection. Darwin’s theory of natural selection
was based on the following observations.
1. Production of more individuals than the environment can support, leads to a struggle
for existence among individuals of a population, with only a fraction of offspring
surviving each generation.
2. Survival in the struggle for existence is not random,, but depends in part on the
hereditary constitution of the surviving individuals. Those individuals whose inherited
characteristics it them best to their environment are likely to leave more offspring
then the less it individuals.
3. This unequal ability of individuals to survive and reproduce will lead to a gradual
change in a population, with favorable characteristics accumulating over the
generations thus leading to the evolution of a new species.