Table 2. Trait heritability results.

Sulcus	h2	h2 SE	h2 P-value	n	Significant covariates	Average length	Vp	Va
arsp*	0.354	0.081	<0.001	675	Age2, CC	15.9	5.911	2.092
cs*	0.281	0.076	<0.001	621	Sex, CC	95.84	8.497	2.388
iar	0.053	0.072	0.178	670	Age, age-by-sex, age2, CC	60.2	25.418	1.347
ips*	0.133	0.075	0.002	491	Age, age-by-sex, CC	75.72	12.936	1.721
lf*	0.235	0.103	<0.001	429	Sex, CC	99.34	18.579	4.366
lu*	0.197	0.121	0.01	360	Sex, CC	75.73	10.836	2.135
ps*	0.512	0.113	<0.001	541	Age, sex, age-by-sex, CC	59.49	5.385	2.757
sar	0.053	0.048	0.077	574		27.504	18.635	0.988
spcd	0.01	0.045	0.406	507		35.793	17.301	0.173
sts*	0.114	0.09	0.036	359	Sex, age, age-by-sex, age2, CC	115.86	15.184	1.731
Larsp_ yn	—		0.5	627		0.812
Lcs_forked*	0.134	0.097	0.021	606		0.606
Lspcd _yn	—		0.5	663		0.905
Rarsp _yn*	0.129	0.070	0.003	737		0.826
Rcs_forked	0.065	0.060	0.076	669		0.590
Rspcd_ yn*	0.15		0.019	747		0.876

Heritability (h²) estimates, heritability standard errors (SE), and significance (P) calculated for each of the 10 metric sulcal length measures (boldface) and 6 nonmetric traits (roman). Significant results are indicated with asterisks by the trait name. Covariates that emerged as significant for that trait during screening and the trait sample size are listed. Age-by-sex is the interaction between age and sex; CC is cranial capacity. Sulcus average lengths are in millimeters. “Average length” reports for nonmetric traits are the frequency of occurrence of the presence of that trait for arsp and spcd phenotypes and the frequency of forked cs. Vp is the phenotypic variation for traits; Va is the additive genetic variation for traits.