One of the overarching pieces of evidence for the evolution of life on earth is the idea of a nested hierarchy. There are several ways to categorize different items, but things related by a common ancestor will show a particular pattern of categorization.
For instance, let's consider automobiles. Automobiles could be classified by make, then by model, then by year. Or they could be classified by year, then by make, then by model. Or any other myriad classification schemes, all of which would be correct. If two people start with a list of cars, they will both come up with perfectly valid yet very different classification ideas. This is because automobiles are each created independently; while they share an "evolution" of sorts as far as technology goes, each car is created as its own separate entity.
But compare this with languages. Assuming you are familiar with language, you would classify Spanish and French together as Romance languages, and English and Scots under Old English, and Old English under West Germanic. Languages can only be classified in one way, and two different people starting with the same data will arrive at the same classification scheme.
This is called a nested hierarchy, and alone is enough to show strong evidence of common ancestry.
Life on earth shows this type of pattern of groups nested within groups nested within groups. Of the animals with a backbone, there are mammals. Within mammals, there are marsupials and placentals. Within placentals are cows, and bats, etc on down to individual species. While some of the details of specific family groups are still controversial, life shows this unique pattern which alone is strongly indicative of common descent.
Following from this principle, biologists can construct family trees of different groups which aid in classification and predictions in fields as diverse as embryology and paleontology. For instance, the family tree of baleen and toothed whales predicts a common ancestor around 35 million years ago that has features of both, and this fossil has been found.
Nested hierarchy alone is almost enough evidence to strongly imply common descent, if not directly the idea of the Darwinian mechanism of random mutation coupled with natural selection.
Martin Kulp is a writer with many distinct interests. He owns several websites on a variety of topics, one of which is information about prostate cancer. See his article on prostate cancer treatment centers at http://prostaide.org/prostate-cancer-treatment-center-options
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