Figure 1

Network characteristics. (A) Cumulative growth in authorship and co-authorship over time have both been nearly log-linear; (B) Network density decreases asymptotically from 45.5% in 1946 to 0.16% in 2018; modularity follows a sigmoid pattern with a period of linear increase between 1960–80 followed by a plateau at high modularity; assortativity rapidly increases in early decades; median normalized PageRank decreases to a low plateau from the 1970s onward; (C) Subspecialties develop at different but broadly parallel rates, with seminal events apparently preceding accelerations of individual subspecialties, e.g.,: (1) in the four years after 1973, combination therapy (AC²⁵), adjuvant therapy²⁶, and tamoxifen²⁷ were introduced in breast cancer; (2) thalidomide²⁸ and bortezomib²⁹ were reported to be efficacious for multiple myeloma; and (3) immunotherapy (ipilimumab^30,31) was introduced in the treatment of melanoma.