nonconstancy of species
This is exhibited by the finches species of the Galapagos islands. While the finches belong to one species, they had phenotypic variations in beak sizes. Some had long narrow beaks while other had short stout beaks with variation in between. This increases the allele (genetic variation) in a gene pool.
branching evolution
The hip bone in whales which is homologous to that of humans depicts branching evolution. This exhibits that both species shared a common ancestor before they branched into different species. The hip in the whale has become vestigial while in humans it is prominent due to its purpose in the human gait and locomotion.
occurrence of gradual changes in species
Older fossils of a species best depict gradual change. This is when they are compared to those of current fossils of the same species. These fossils have displayed gradual differences in their structure and shapes. This is evident in the fossil of humans species that has shown gradual differences in structures such as the size and shape of the skull.
natural selection as the mechanism for evolution
When the predators such as lions during their hunting have preferences for fat prey (antelopes) since they are slower and provide more meat, this is natural selection forces at work on the prey population. The population of the fat and slow antelope will reduce because of being fed on more than the others. Therefore the subsequent generation of the antelope population will weed out fat antelopes.
These are the four evolution theory given by Darwin. The non-constancy of species, Branching evolution, Natural selection, and gradual changes in species.
Charles Robert Darwin was the scientist who was the geologist and biologist.
The non-constancy of species:
The non constancy can be seen in the finches of Galápagos island.
In these finches there were changes in the beak which produce new species.
It says that every species is unique.
Branching evolution:
Branching evolution can be seen as the homologous organs are present in different organisms.
It shows that these organisms were evolved from a same ancestor before they branched into new species.
Occurrence of gradual changes in species:
It says that a species changes gradually over time, but not always into a new species.
This can be seen in human fossils of former time and current time.
Natural selection as the mechanism for evolution:
Natural selection is a process in which nature selects the species which are more perfectly living to a next generation.
Thus, these are the four theories of evolution given by Darwin.
Learn more about evolution, here:
https://brainly.com/question/2725702
