Figure S1 . Histogram depicting the distribution of the relatedness estimates between leader and follower pairs
(N=25). This distribution closely mirrors the distribution of pairwise relatedness estimates reported by Van Horn et al. [1] for a set of 2,006 pairs of known non-relatives in wild baboon population, supporting our conclusion that the majority of leader-follower pairs were unrelated.

Figure S2 . Histogram depicting the distribution of the complete (N=11), left-censored (N=18) and right-censored
(N=18) leader tenures.

Follower Censoring:
We used 27 follower tenures where we knew the exact date of their unit entry. We had complete tenure information for 17 of these data points. The remaining 10 followers were still in their respective units when the study period ended - making them right-censored data. The distributions of the right-censored and complete follower tenures are not very similar (Figs. S3 &
S4). However, 8 of the 10 right-censored data points were either old followers or followers who had sired offspring. As such, those followers actually had longer tenures than the data that were included in the model (although we could not measure how much longer as the study period had ended). Therefore our findings (that old followers and followers who sired offspring had longer tenures than new followers and follower who did not sire offspring) would not be different if we had complete tenure information for these 10 followers - if anything, complete tenure information would strengthen our result.
Figure S3 Histogram depicting the distribution of the incomplete (N=10) and complete (N=17) follower tenures.

Figure S4 Quantile-quantile plot of the right-censored and complete follower tenures. Quantile-quantile plots compare the shapes of two distributions, by grouping each data set into equal-sized subsets of values (quantiles). If two groups of data come from similar distributions, their Q-Q plot should exhibit an approximately linear relationship, as do our data sets.

REFERENCES FOR SUPPLEMENTARY MATERIAL
1 Van Horn, R. C., Altmann, J. & Alberts, S. C. 2008 Can’t get there from here: inferring kinship from pairwise genetic relatedness. Animal Behaviour 75 , 1173–1180.