Evolution is a unifying principle in biology. It is the change in the genetic makeup of a population over time. It can broadly be categorized into two types based on the scale. These are macroevolution and microevolution.
There are various types of pieces of evidence as far as evolution is concerned. These provide evidence for and can allow us to reconstruction macroevolutionary events. Here are some of the proofs of evolution.
Darwin thought of evolution as a decent modification, a process whereby species change and give rise to new ones over many generations. He proposed that the evolutionary history of life forms a branching tree with levels in which all species can be traced to an ancient common ancestor. In the tree, more closely related groups of species have more recent common ancestors, and every group shares features which were present in its last common ancestor. This idea can be used to work backward and figure out how organisms are related based on shared features.
Like structural homologies, similarities between biological molecules can also reflect shared evolutionary ancestry. All living organisms at the most basic level share the same DNA, genetic codes, basic gene expression, and molecular building blocks. These shared features suggest that living things are descended from a common ancestor and that the ancestor had DNA as its genetic material, expressed its genes by translation and transcription and used the genetic code. Present-day organisms share these features since they were inherited from the ancestor.
Geographical distribution of organisms on earth follows patterns which are best explained by evolution, in combination with tectonic plates movement over geological time. For instance, broad groupings of organisms which had already evolved before the breakup of the subcontinental Pangea tend to be distributed worldwide. In contrast broad groupings which evolved after the breakup appear uniquely in smaller regions on earth. For example, there are unique groups of animals and plants on the southern and northern continents which can be traced to the split of the Pangea.
Fossils are the preserved remains of previously living organisms or their traces, dating from distant past. The fossil record is not complete or unbroken, most organisms never fossilize, and humans rarely find even those that do. Nonetheless, the fossils which humans have collected offer unique insights time evolution over long timescales.
The fossils are usually contained in rocks which build up in layers known as strata. The strata provide some sort of timeline. The layers near the top are newer while those near the bottom older. Fossils found in the different strata at the same site are ordered by their positions and reference strata with unique features can be used to compare the ages of the fossils across locations. Scientists can roughly date fossils using radiometric dating, a process which measures the radioactive decay of elements.
These are some of the pieces of evidence that have been used to prove the theory of evolution. They show that organisms had a common ancient ancestor. Such information is available in archaeological sites.