Evolvability and craniofacial diversification in genus Homo

Abstract

There is abundant theoretical and empirical evidence for the influence of variational properties of populations on microevolution, and more limited support for their lasting impact during macroevolution. This study applies evolutionary quantitative genetic approaches to assess the long-term impact of within-population phenotypic variation and covariation (the P matrix) on population divergence in recent humans and species diversification in genus Homo. Similarity between the primary axes of within-and between-population craniofacial variation confirms a role for p max in human population divergence, although diversification is not constrained to be unidimensional. The long term impact of the P matrix on craniofacial evolution is supported by higher-thanaverage evolvabilities along most branches of the Homo tree, but statistical uncertainty inherent in the data reduce confidence in this conclusion. Higher evolvability is not statistically correlated with increased rate of evolution, although the relationship is in the predicted direction. This is due in part to the high evolutionary rate on the early modern human branch despite its moderate level of evolvability. There was evidence for neutral evolution as well as directional and stabilizing selection during evolution of our genus during the Plio-Pleistocene using generalized genetic distance as a test statistic. K E Y W O R D S :Craniofacial diversification, evolutionary rate, evolvability, Homo, neutral evolution, selection.

Reconstructing cranial evolution in an extinct hominin

“…Therefore, the recent H. sapiens pooled within-population P matrices for the occipital and frontal bones were used as proxies for H. erectus. H. sapiens was chosen because it is the closest extant phylogenetic match for H. erectus [49,52,80] and the human P matrix is a good estimate of its G matrix [81][82][83]. In total, 145 recent H. sapiens from three populations with n ∼ 50 each were used to calculate the pooled within-population covariance matrices that were used as proxies for H. erectus in testing Prediction 3 (electronic supplementary material, table S3).…”

What does modularity mean?

“…Not surprisingly, these models have inspired a large literature (e.g., Baab, 2018; Goswami et al, 2014; Grabowski et al, 2011; Haber, 2016; Marroig et al, 2009; Shirai & Marroig, 2010). Most estimate phenotypic rather than genetic covariance matrices and compare these among taxa before reconstructing selection gradients and analyzing the directions and rates of evolutionary change One recent study estimated G for seven species of West Indian Anolis lizards and found that evolutionary change is strongly biased in the direction of the major axis of G for over 40 million years even though G itself evolved (McGlothlin et al, 2018).…”

Evolvability in the fossil record

“…In addition, the richness of the fossil record varies substantially among taxa, and not all fossil species have sufficient sample sizes to robustly estimate P. Cheverud (1988) suggested at least 40 individuals were needed for a reasonably accurate P for G substitution, but larger sample sizes are required as the number of traits increase and to accurately estimate some evolvability statistics (Grabowski and Porto 2017). One potential solution is to use P (or G) matrices from extant species as a substitute for unknown fossil G matrices (Ackermann and Cheverud 2004;Young et al 2010;Grabowski et al 2011;Hansen and Voje 2011;Grabowski and Roseman 2015;Baab 2018). This assumes that the estimated P or G from the extant population is similar enough to G in the ancestral, extinct population.…”