Table 1. d_N/d_S ratios in the HERV-K(HML2) family and related exogenous β retroviruses.

		One-ratio model (=1)	Two-ratio model (=2)
Family	Gene	Whole tree	Internal branches*	Terminal branches	Likelihood difference (2 - 1)	P value†
HERV-K(HML2) (44 elements)	All	0.52	0.21	0.67	142	<0.001
	gag	0.53	0.28	0.68	26	<0.001
	pol	0.47	0.16	0.62	91	<0.001
	env	0.62	0.26	0.79	31	<0.001
Exogenous viruses (7 elements)	All	0.10	0.10	0.10	0.01	NS
	gag	0.09	0.09	0.10	0.05	NS
	pol	0.07	0.06	0.08	0.67	NS
	env	0.17	0.14	0.18	0.85	NS

^*Excluding the segmentally duplicated clade (see Table 3).

^†Taken from critical values on the χ² distribution. NS, not significant.