Data from: Coevolution drives the emergence of complex traits and promotes evolvability

The evolution of complex organismal traits is obvious as a historical
fact, but the underlying causes—including the role of natural
selection—are contested. Gould argued that a random walk from a
necessarily simple beginning would produce the appearance of increasing
complexity over time. Others contend that selection, including
coevolutionary arms races, can systematically push organisms toward more
complex traits. Methodological challenges have largely precluded
experimental tests of these hypotheses. Using the Avida platform for
digital evolution, we show that coevolution of hosts and parasites greatly
increases organismal complexity relative to that otherwise achieved. As
parasites evolve to counter the rise of resistant hosts, parasite
populations retain a genetic record of past coevolutionary states. As a
consequence, hosts differentially escape by performing progressively more
complex functions. We show that coevolution's unique feedback between
host and parasite frequencies is a key process in the evolution of
complexity. Strikingly, the hosts evolve genomes that are also more
phenotypically evolvable, similar to the phenomenon of contingency loci
observed in bacterial pathogens. Because coevolution is ubiquitous in
nature, our results support a general model whereby antagonistic
interactions and natural selection together favor both increased
complexity and evolvability.