Polytomy

Most polytomies are soft, meaning that they would be resolved into a typical tree of dichotomies if better data were available.

[6] In particular situations, they may be common, for example when a species that has rapidly expanded its range or is highly panmictic undergoes peripatric speciation in different regions.

In contrast, a soft polytomy stems from branches on gene trees of finite temporal duration but for which no substitutions have occurred.

In practical terms, the ability to distinguish between hard and soft polytomies is limited: if for example a kilobase of DNA sequences that mutate approximately 1% per million years is analyzed, lineages diverging from the same ancestor within the same 100,000 years cannot be reliably distinguished as to which one diverged first.

This can easily confound molecular clock algorithms to the point where hard polytomies become unrecognizable as such.