The phylogenetic relationships between three sequences s i , s j and s k , sampled on dates t i , t j and t k respectively As nucleotide data increases without bound, K ij → D ij and → p ij , ensuring that → α ij . For finite sequence lengths, this relation ensures that . To gain an understanding of this estimator, we note that with a standard model of substitution (e.g. JC69, HKY85), a rate of substitution of 10 -4 (s/s/yr) and a sequence of 2000 nucleotides, the above estimator yields a standard error of approximately 23 years [20] .