Editing Fossil (section)

=== Linnaeus and Darwin ===
Early [[natural science|naturalists]] well understood the similarities and differences of living species leading [[Carl Linnaeus|Linnaeus]] to develop a hierarchical classification system still in use today. Darwin and his contemporaries first linked the hierarchical structure of the tree of life with the then very sparse fossil record. Darwin eloquently described a process of descent with modification, or evolution, whereby organisms either adapt to natural and changing environmental pressures, or they perish.

When Darwin wrote ''[[On the Origin of Species|On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life]]'', the oldest animal fossils were those from the [[Cambrian]] Period, now known to be about 540&nbsp;million years old. He worried about the absence of older fossils because of the implications on the validity of his theories, but he expressed hope that such fossils would be found, noting that: "only a small portion of the world is known with accuracy." Darwin also pondered the sudden appearance of many groups (i.e. [[phylum|phyla]]) in the oldest known Cambrian fossiliferous strata.<ref>{{Citation|last=Darwin|first=Charles|chapter=[[:s:The Origin of Species (1872)/Chapter X|Chapter X: On the Imperfection of the Geological Record]]|title=[[On the Origin of Species|The Origin of Species]]
| author-link= Charles Darwin
| year = 1872
| place= London| publisher= John Murray
}}</ref>