Table 2. d_N/d_S ratios of the env gene on internal branches of trees from representative HERV families.

Class	Family	No. of elements	dN/dS	P value*
I	HERV-E	26	0.22	<0.001
	HERV-H†	60	0.24	<0.001
	HERV-T‡	12	0.12	<0.001
	HERV-R	9	0.45	0.05-0.1
II	HERV-HML3	91	0.73	<0.05
	HERV-HML5	30	0.40	<0.001
	HERV-HML6	15	0.35	<0.001
III	HERV-S	34	0.21	<0.001

The significance of the difference in likelihood if this ratio is fixed at 1 is shown.

^*Taken from critical values on the χ² distribution.

^†Only for HERV-H elements that have an intact env.

^‡Excluding elements copied by segmental duplication; this family is also termed HERV-S71.