Wikipedia mentions "Since animal mtDNA evolves faster than nuclear genetic markers" with a few sources.

Some sources:
* <Power, Sex, Suicide by Nick Lane (2006)> page 361 mentions:
  > While nuclear DNA can barely distinguish between chimps and humans, the mitochondrial clock ticks fast enough to reveal differences accumulating over tens of thousands of years
  so this property is also important for the <human mitochondrial molecular clock>.
* https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3350313 says it for metazoans
* https://www.quora.com/Why-does-mitochondrial-DNA-mutate-faster


 Mitochondrial DNA mutates faster than nuclear DNA

ID: mitochondrial-dna-mutates-faster-than-nuclear-dna