Difference Between Maximum Parsimony and Maximum Likelihood

The key difference between maximum parsimony and maximum likelihood depends on the method used in developing the phylogenetic tree. Maximum parsimony focuses on minimizing the total character states during the phylogenetic tree construction while the maximum likelihood is a statistical approach in drawing the phylogenetic tree depending on the likelihood between genetic data.

Phylogeny is the novel approach towards classification and nomenclature of organisms. Phylogeny relies on genetic data and evolutionary relationships. The genetic data is a result of DNA sequencing. In phylogeny, classification of organisms takes place based on the common ancestor. Maximum parsimony and maximum likelihood of a phylogenetic relationship increase the accuracy and reliability of a phylogenetic tree.

CONTENTS

1. Overview and Key Difference
2. What is Maximum Parsimony 
3. What is Maximum Likelihood
4. Similarities Between Maximum Parsimony and Maximum Likelihood
5. Side by Side Comparison – Maximum Parsimony vs Maximum Likelihood  in Tabular Form
6. Summary

What is Maximum Parsimony?

In the technique of maximum parsimony, the minimizing of the total character state changes takes place during the phylogenetic analysis. Phylogenetic is a branch of biology that deals with studying evolutionary relationships. A phylogenetic tree is a tree that shows the evolutionary relationships based on a common ancestor. Thus, when drawing a phylogenetic tree using the concept of maximum parsimony, the amount of parallel evolution is minimized. Therefore, maximum parsimony will generate the tree much quicker than other methods. It is because only the main distinguishing characteristics are considered in maximum parsimony.

When drawing a maximum parsimonious tree, the tree is always the shortest possible tree with the minimum number of taxa. However, the reliability of a maximum parsimonious tree is very high. The statistical consistency and the accuracy of the phylogenetic relationship based on maximum parsimony will vary. Moreover, there are complex algorithms that analyze the maximum parsimony of a phylogenetic relationship.

What is Maximum Likelihood?

Maximum likelihood is one of the most used statistical methods that analyzes phylogenetic relationships. The method will analyze phylogeny based on the probability model. Further, this method takes both mean and variance into consideration. Thus, in phylogeny, maximum likelihood is obtained on the given genetic data of a particular organism.

There are both advantages and disadvantages of using the statistical method of maximum likelihood. The method is very appropriate when analyzing a simple data set containing genetic information. When the degree of variance among the genetic data is lower, the maximum likelihood scores are reliable. The results generated through maximum likelihood further confirms the maximum parsimony scores of a particular phylogenetic relationship. Therefore, maximum likelihood analysis acts as a confirmative test.

In comparison to the advantages mentioned above, this method is a slow and intense process. Furthermore, in the absence of a single data set, the error output is high. Thus, it also makes reproducibility of the results more difficult by the maximum likelihood estimation.

What are the Similarities Between Maximum Parsimony and Maximum Likelihood?

• Maximum parsimony and maximum likelihood are two approaches that play an important role in phylogeny.
• Both techniques depict the relationship of an organism to its ancestor based on the genetic data available.
• Phylogenetic trees can be interpreted using both maximum parsimony and maximum likelihood.
• In both techniques, the genetic data relies on DNA sequencing or RNA sequencing.
• Both methods are important in generating phylogenetic trees.

What is the Difference Between Maximum Parsimony and Maximum Likelihood?

Both maximum parsimony and maximum likelihood are two different approaches in interpreting a phylogenetic tree. Maximum parsimony believes in analyzing few characteristics and minimizing the character changes from organism to organism. In contrast, the maximum likelihood method takes both mean and the variance into consideration and obtain maximum likelihood on the given genetic data of a particular organism. So, this is the key difference between maximum parsimony and maximum likelihood.

Furthermore, the reliability of maximum parsimony alone is not adequate to derive a conclusion. But, the maximum likelihood method acts as a confirmative test of the results of maximum parsimony. Thus, conclusions should be done using both maximum parsimony and maximum likelihood.

The below infographic summarizes the difference between maximum parsimony and maximum likelihood.

Summary – Maximum Parsimony vs Maximum Likelihood

Phylogeny plays an important role in deriving evolutionary relationships by constructing phylogenetic trees. Maximum parsimony is the technique of constructing a tree with the minimum number of character state change. In contrast, the maximum likelihood of a phylogenetic tree relies on using the maximum similarity between genetic data. The data for both analyses come from the DNA or RNA sequence data. The reliability and accuracy are high when the tree construction takes place using both the techniques. Thus, this summarizes the difference between maximum parsimony and maximum likelihood.

Reference:

1. Elliott. “Contest Between Parsimony and Likelihood.” OUP Academic, Oxford University Press, 1 Aug. 2004, Available here.

Image Courtesy:

1. “Maximum parsimony tree of haplogroup B2b” By Taboada-Echalar P, Álvarez-Iglesias V, Heinz T, Vidal-Bralo L, Gómez-Carballa A, Catelli L, et al. (2013) The Genetic Legacy of the Pre-Colonial Period in Contemporary Bolivians. PLoS ONE 8(3): e58980. doi:10.1371/journal.pone.0058980 (CC BY 2.5) via Commons Wikimedia
2. “Maximum-Likelihood-Tree of Lactarius blennius and relativs” By User:Thkgk – Own work (CC0) via Commons Wikimedia