Editing Occam's razor (section)

=== Biology ===
{{Citation style|date=January 2023|section}}
Biologists or philosophers of biology use Occam's razor in either of two contexts both in [[evolution|evolutionary biology]]: the units of selection controversy and [[systematics]]. [[George C. Williams (biologist)|George C. Williams]] in his book ''[[Adaptation and Natural Selection]]'' (1966) argues that the best way to explain [[altruism]] among animals is based on low-level (i.e., individual) selection as opposed to high-level group selection. Altruism is defined by some evolutionary biologists (e.g., R. Alexander, 1987; W. D. Hamilton, 1964) as behavior that is beneficial to others (or to the group) at a cost to the individual, and many posit individual selection as the mechanism that explains altruism solely in terms of the behaviors of individual organisms acting in their own self-interest (or in the interest of their genes, via kin selection). Williams was arguing against the perspective of others who propose selection at the level of the group as an evolutionary mechanism that selects for altruistic traits (e.g., D. S. Wilson & E. O. Wilson, 2007). The basis for Williams's contention is that of the two, individual selection is the more parsimonious theory. In doing so he is invoking a variant of Occam's razor known as [[Morgan's Canon]]: "In no case is an animal activity to be interpreted in terms of higher psychological processes, if it can be fairly interpreted in terms of processes which stand lower in the scale of psychological evolution and development." (Morgan 1903).

However, more recent biological analyses, such as [[Richard Dawkins]]'s ''[[The Selfish Gene]]'', have contended that Morgan's Canon is not the simplest and most basic explanation. Dawkins argues the way evolution works is that the genes propagated in most copies end up determining the development of that particular species, i.e., natural selection turns out to select specific genes, and this is really the fundamental underlying principle that automatically gives individual and group selection as [[Emergent evolution|emergent]] features of evolution.

[[Zoology]] provides an example. [[Muskox]]en, when threatened by [[Gray wolf|wolves]], form a circle with the males on the outside and the females and young on the inside. This is an example of a behavior by the males that seems to be altruistic. The behavior is disadvantageous to them individually but beneficial to the group as a whole; thus, it was seen by some to support the group selection theory. Another interpretation is kin selection: if the males are protecting their offspring, they are protecting copies of their own alleles. Engaging in this behavior would be favored by individual selection if the cost to the male musk ox is less than half of the benefit received by his calf – which could easily be the case if wolves have an easier time killing calves than adult males. It could also be the case that male musk oxen would be individually less likely to be killed by wolves if they stood in a circle with their horns pointing out, regardless of whether they were protecting the females and offspring. That would be an example of regular natural selection – a phenomenon called "the selfish herd".

[[Systematics]] is the branch of [[biology]] that attempts to establish patterns of relationship among biological taxa, today generally thought to reflect evolutionary history. It is also concerned with their classification. There are three primary camps in systematics: cladists, pheneticists, and evolutionary taxonomists. Cladists hold that classification should be based on [[synapomorphies]] (shared, derived character states), pheneticists contend that overall similarity (synapomorphies and complementary [[symplesiomorphies]]) is the determining criterion, while evolutionary taxonomists say that both genealogy and similarity count in classification (in a manner determined by the evolutionary taxonomist).<ref>{{Cite book |title=Reconstructing the Past: Parsimony, Evolution, and Inference |last=Sober |first=Elliot |date=1998 |publisher=The MIT Press |isbn=978-0-262-69144-4 |edition=2nd |location=Massachusetts Institute of Technology |page=7}}</ref><ref>{{Cite book |title=Phylogenetics: the theory and practice of phylogenetic systematics |last=Wiley |first=Edward O. |date=2011 |edition=2nd |publisher=Wiley-Blackwell |isbn=978-0-470-90596-8}}</ref>

It is among the cladists that Occam's razor is applied, through the method of ''cladistic parsimony''. Cladistic parsimony (or [[maximum parsimony]]) is a method of phylogenetic inference that yields [[phylogenetic tree]]s (more specifically, cladograms). [[Cladistics|Cladograms]] are branching,  diagrams used to represent hypotheses of relative degree of relationship, based on [[synapomorphies]]. Cladistic parsimony is used to select as the preferred hypothesis of relationships the cladogram that requires the fewest implied character state transformations (or smallest weight, if characters are differentially weighted). Critics of the cladistic approach often observe that for some types of data, parsimony could  produce the wrong results, regardless of how much data is collected (this is called statistical inconsistency, or [[long branch attraction]]). However, this criticism is also potentially true for any type of phylogenetic inference, unless the model used to estimate the tree reflects the way that evolution actually happened. Because this information is not empirically accessible, the criticism of statistical inconsistency against parsimony holds no force.<ref>{{cite journal | last1 = Brower | first1 = AVZ | year = 2017 | title = Statistical consistency and phylogenetic inference: a brief review | journal = Cladistics | volume =  34| issue = 5| pages =  562–567| doi = 10.1111/cla.12216 | pmid = 34649374 | doi-access = free }}</ref> For a book-length treatment of cladistic parsimony, see [[Elliott Sober]]'s ''Reconstructing the Past: Parsimony, Evolution, and Inference'' (1988). For a discussion of both uses of Occam's razor in biology, see Sober's article "Let's Razor Ockham's Razor" (1990).

Other methods for inferring evolutionary relationships use parsimony in a more general way. [[Likelihood function|Likelihood]] methods for phylogeny use parsimony as they do for all likelihood tests, with hypotheses requiring fewer differing parameters (i.e., numbers or different rates of character change or different frequencies of character state transitions) being treated as null hypotheses relative to hypotheses requiring more differing parameters. Thus, complex hypotheses must predict data much better than do simple hypotheses before researchers reject the simple hypotheses. Recent advances employ [[information theory]], a close cousin of likelihood, which uses Occam's razor in the same way. The choice of the "shortest tree" relative to a not-so-short tree under any optimality criterion (smallest distance, fewest steps, or maximum likelihood) is always based on parsimony.<ref>{{cite book |title =Biological Systematics: Principles and Applications (3rd edn.) |last=Brower &  |first=Schuh |date=2021 |publisher=Cornell University Press}}</ref>

[[Francis Crick]] has commented on potential limitations of Occam's razor in biology. He advances the argument that because biological systems are the products of (an ongoing) natural selection, the mechanisms are not necessarily optimal in an obvious sense. He cautions: "While Ockham's razor is a useful tool in the physical sciences, it can be a very dangerous implement in biology. It is thus very rash to use simplicity and elegance as a guide in biological research."<ref>Crick 1988, p. 146.</ref>  This is an ontological critique of parsimony.

In [[biogeography]], parsimony is used to infer ancient vicariant events or [[Historical migration|migrations]] of [[species]] or [[population]]s by observing the geographic distribution and relationships of existing [[organism]]s. Given the phylogenetic tree, ancestral population subdivisions are inferred to be those that require the minimum amount of change.{{citation needed|date=March 2024}}