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In palaeontology, the evidence for species and evolution comes mainly from the comparative anatomy of fossils. A chronospecies is defined in a single lineage (solid line) whose morphology changes with time. At some point, palaeontologists judge that enough change has occurred that two forms (A and B), separated in time and anatomy, once existed.
Allochronic speciation (also known as allochronic isolation, or temporal isolation) is a form of speciation (specifically ecological speciation) arising from reproductive isolation that occurs due to a change in breeding time that reduces or eliminates gene flow between two populations of a species.
[1]: 230 A rock unit has a characteristic assemblage of fossils, independent of its lithology. [ 1 ] : 229 Thus, the fossils can be used to compare the ages of different rock units. The basic unit of biochronology is the biostratigraphic zone, or biozone , a collection of fossils found together in a rock unit.
Phylogenetic comparative methods (PCMs) use information on the historical relationships of lineages (phylogenies) to test evolutionary hypotheses.The comparative method has a long history in evolutionary biology; indeed, Charles Darwin used differences and similarities between species as a major source of evidence in The Origin of Species.
The idea of a tree of life arose from ancient notions of a ladder-like progression from lower into higher forms of life (such as in the Great Chain of Being).Early representations of "branching" phylogenetic trees include a "paleontological chart" showing the geological relationships among plants and animals in the book Elementary Geology, by Edward Hitchcock (first edition: 1840).
Members of a species are considered to evolve as a single unit (or lineage) when they repeatedly share the same genes. The nodes would represent a split in lineage due to a breaking of genetic connections: when a single lineage is divided into two subsets, with the individuals not exchanging genes, they will accumulate differences in genes.
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One small clade of fish, showing how venom has evolved multiple times. [10]Taxonomy is the identification, naming, and classification of organisms. Compared to systemization, classification emphasizes whether a species has characteristics of a taxonomic group. [6]