Fig. 3: The organization of hierarchical tissues that have evolved to limit somatic evolution.

We consider the least complex tissue, i.e., the one with the smallest number of hierarchical levels that can keep the lifetime risk of cancer below a specific value set by the “drift-barrier” (see Methods for details). a For the hematopoietic system, where N0 = 104 stem cells produce approximately N = 1015 mature cells during an individual’s lifetime we consider a threshold lifetime risk of about 2%. b For the colon, where N0 = 108 and N = 1014 we consider a threshold of about 4%. Each panel shows the value of a given parameter of the least complex tissue for different values of s and μ. For both tissues, the area delimited by the dashed lines corresponds to the most realistic values for μ and s based on the literature, as discussed in the main text. c To explore tissues with different values of N/N0 we keep N = 1015, μ = 10−5 and the maximum acceptable lifetime risk of 2% fixed, but change the ratio N/N0. The dashed line corresponds to the value for the hematopoetic system.