“…To model how various individual-, dyadic-, and blocklevel covariates are related to the probability of network tie formations, we use a generalization of the Social Relations Model (Kenny and La Voie, 1984;Snijders and Kenny, 1999), which integrates block-level random effects (see Redhead, McElreath and Ross, 2022;Ross, McElreath and Redhead, 2022, for technical outlines and tutorials). Specifically, we estimate the probability of a directed tie between two individuals in the friendship network, 𝐹 , as a function of: sex, 𝑆, ethnic group, 𝐸, religious group, 𝑅, age, 𝐴, physical attractiveness, 𝑃 , BMI, 𝐵, years of education, 𝑈 , grip strength, 𝐺, reproductive success, 𝑄, log wealth, 𝑊 , RICH giving propensity, 𝑍, RICH leaving propensity, 𝐿, dyadic spatial distance, 𝐷, dyadic age distance, Ā, dyadic attractiveness distance, P , dyadic BMI distance, B, dyadic education distance, Ū , dyadic political opinion difference, 𝑂, dyadic log wealth distance, W , relatedness, 𝐾, food/money sharing ties, 𝑀, dyadic RICH giving, Z, and dyadic RICH leaving, L.…”