Darwin’s theory of evolution by natural selection states that all species of living things have evolved from simple life forms that first developed more than three billion years ago
Acceptance
The theory of evolution by natural selection was only gradually accepted
The theory challenged the idea that God made all the animals & plants that live on Earth
There was insufficient evidence at the time the theory was published to convince many scientists
The mechanism of inheritance & variation was not known until fifty years after the theory was published
Other theories, including that of Lamarck, are based mainly on the idea that changes that occur in an organism during its lifetime can be inherited, though it is now accepted that in the vast majority of cases this type of inheritance cannot occur
Evolutionary relationships
Studying the similarities & differences between organisms allows the classification of living organisms into animals, plants and microorganisms, as well as the understanding of evolutionary & ecological relationships
Models can be used to suggest relationships between organisms
Evolutionary trees are models that can be drawn to show the relationships between different groups of organisms, wherein the meeting of two branches denotes a common ancestor between the two groups of organisms
Natural selection
Individual organisms within a particular species may show a wide range of variation because of differences in their genes caused by mutations
Individuals with characteristics most suited to the environment are more likely to survive to breed successfully
The genes that have enabled these individuals to survive are then passed on to the next generation
Evolution of a new species can take millions of years but sometimes evolution of a population occurs in a relatively short time, such as antibiotic resistance in bacteria