Table 1.

Data and negative binomial regression

	Data		Influence of mutation spectrum
Species	Paths	Events	β	$p_{\beta }$
S. cerevisiae	534	713	1.05 ±0.08	$<{10}^{-16}$
E. coli	492	602	0.98 ±0.14	$<{10}^{-11}$
M. tuberculosis	283	4,413	0.85 ±0.23	$<{10}^{-3}$

Shown are the observed numbers of paths and events for adaptive changes in the three datasets, along with calculated values for the mutation coefficient β (with SE) and its P value.