This event usually occurs when a few organisms end up in new, often distant areas or when environmental changes cause several extinctions, opening up ecological niches for the survivors. The events that cause these species to originally separate from each other over distant areas may still allow both of the species to have equal chances of surviving, reproducing, and even evolving to better suit their environments while still being two distinct species. An example of cladogenesis today is the Hawaiian archipelago, to which stray organisms traveled across the ocean via ocean currents and winds. Most of the species on the islands are not found anywhere else on Earth due to evolutionary divergence.
Cladogenesis is in contrast to anagenesis, in which an ancestral species gradually accumulates change, and eventually, when enough is accumulated, the species is sufficiently distinct and different enough from its original starting form that it can be labeled as a new form - a new species. Note that here the lineage in a phylogenetic tree does not separate.
There are many different methods and forms of evidence that can be used when it comes to determining whether or not a speciation event falls under cladogenesis or not. Below are a few different methods used by scientists, with a quick explanation or example for each:
- Simulations: This involves the process of taking already known information (such as mitochondrial information) about a species and running the information through a computer to see if a cladogenetic event is the most probable explanation for a species existence. This way of studying species is the most practical. A lot of times, case studies and constructing experiments can cost a lot of money and takes time, so it is easier to plug information into a computer and allow the computer to run different scenarios to test for accuracy.
- Morphological/Paleontological Evidence: Using fossil evidence can determine whether or not two species were alive at the same time. However, there are some drawbacks to using just fossil evidence, because fossil evidence can only differentiate species on an assemblage level.
- Molecular Evidence: Molecular data can be used to see how the genome or DNA of specific species has diverged. This, along with the fossil evidence, can be a good basis for seeing if two distinct species came from a similar ancestral species and if they were both alive at the same time.
- Models: This involves taking already-alive species and running experiments (simulating possible environments for example) to see if speciation occurs in order to explain the presence of different species or if there is an alternate explanation for the species. This is sometimes the most accurate way of measuring speciation because it gives actual life results, as opposed to computer generated data.
These are just a few examples of ways to distinguish a speciation event as either cladogenetic or anagenetic. Scientists are constantly coming up with new ways to study species and determine how they are related to each other and what may have caused their splitting.
- Gould, Stephen Jay, & Eldredge, Niles (1977). "Punctuated equilibria: the tempo and mode of evolution reconsidered." Paleobiology 3 (2): 115-151. (p.145)
- Strotz LC, Allen AP. Proc Natl Acad Sci U S A. 2013 Feb 19; 110(8):2904-9. Epub 2013 Feb 1
- Korotayev, Andrey (2004). World Religions and Social Evolution of the Old World Oikumene Civilizations: A Cross-cultural Perspective (First Edition ed.). Lewiston, New York: Edwin Mellen Press. ISBN 0-7734-6310-0. (on the applicability of this notion to the study of social evolution).
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