Molecular clock calculations estimate the origin of stem group Malpighiales at around 100 Mya ( million years ago ) and the origin of crown group Malpighiales at about 90 Mya.

Molecular phylogenetics has also been used to estimate the dates when species diverged, but there is controversy about the reliability of the molecular clock on which such estimates depend.

Molecular clock and fossil dating suggest echidnas split from platypuses 19 – 48 million years ago.

* Molecular clock

Molecular clock users have developed workaround solutions using a number of statistical approaches including maximum likelihood techniques and later Bayesian modeling.

* Molecular clock explanation of the molecular equidistance phenomenon

simple: Molecular clock

# REDIRECT Molecular clock

Molecular clock analyses suggest that P. falciparum is as old as the human line ; the two species diverged at the same time as humans and chimpanzees.

Molecular clock analyses suggest that the ancestor of the nesomyines colonized Madagascar about 20-25 million years ago.

Molecular phylogenetic analysis has lent support to this hypothesis, and it is now generally accepted.

This approximation, which reflects the " molecular clock " hypothesis that a roughly constant rate of evolutionary change can be used to extrapolate the elapsed time since two genes first diverged ( that is, the coalescence time ), assumes that the effects of mutation and selection are constant across sequence lineages.

( In the case of nucleotide sequences, the molecular clock hypothesis in its most basic form also discounts the difference in acceptance rates between silent mutations that do not alter the meaning of a given codon and other mutations that result in a different amino acid being incorporated into the protein.

While unrooted trees can always be generated from rooted ones by simply omitting the root, a root cannot be inferred from an unrooted tree without some means of identifying ancestry ; this is normally done by including an outgroup in the input data or introducing additional assumptions about the relative rates of evolution on each branch, such as an application of the molecular clock hypothesis.

The molecular clock ( based on the molecular clock hypothesis ( MCH )) is a technique in molecular evolution that uses fossil constraints and rates of molecular change to deduce the time in geologic history when two species or other taxa diverged.

Together with the work of Emile Zuckerkandl and Linus Pauling, the genetic equidistance result directly led to the formal postulation of the molecular clock hypothesis in the early 1960s.

Researchers such as Ayala have more fundamentally challenged the molecular clock hypothesis .< ref name = Ayala99 > According to Ayala's 1999 study, 5 factors combine to limit the application of molecular clock models:

These models are called relaxed molecular clocks because they represent an intermediate position between the ' strict ' molecular clock hypothesis and Felsenstein's many-rates model and are made possible through MCMC techniques that explore a weighted range of tree topologies and simultaneously estimate parameters of the chosen substitution model.

UPGMA assumes a constant rate of evolution ( molecular clock hypothesis ), and is not a well-regarded method for inferring relationships unless this assumption has been tested and justified for the data set being used.