Significance of interaction preferences by protein age and origin. Proteins preferentially interact with other proteins of the same age and origin. The top line in each box gives the number of observed interactions of each type and the number expected based on 1,000 random networks. The middle line gives the effect size (Glass's Δ), and the bottom line gives an empirical p-value for the difference between the observed and expected (Methods). Squares in red indicate significantly more interactions than expected; blue indicates significantly fewer than expected; and black indicates no significant difference. The red trend across the diagonal reflects the significant preference for proteins to interact within their age/origin group. Nearly all of the off-diagonal interactions are significantly depleted. The only significant enrichment for interactions between proteins of different age or origin is among young proteins.