As noted above, the noisy nature of these results can likely be attributed to relatively small sample size for this type of analysis. We conjectured that if this were the case, and assuming both study samples were homogeneous, combining the Davis et al. heritability estimates and our heritability estimates, per chromosome, would produce a somewhat better fit between heritability per chromosomes and length. This result is confirmed in Figure 2C–D; the fit of the regression for this weighted average heritability (weights proportional to the inverse of variance), adjusted R2 = 0.31, is better than the fit for our sample alone, adjusted R2=0.27. Furthermore, note that chromosome 6, which had very low heritability in Davis et al., shows reasonable heritability in both our analyses and in the combined data, again suggesting small sample sizes are driving some of the results.
