“In 1976 Van Valen argued that ecology drives evolution, and selection acts primarily on phenotypes, not genotypes”
Cannabis sativa has undergone two rounds of evolution—millions of years (mya) of natural
selection, and thousands of years (kya) of human selection. Cannabis and Humulus diverged from a common ancestor, with a divergence time, based on molecular clock analyses, of 27.8 mya (McPartland 2018), 21 mya (Zerega et al. 2005), or 18.2 mya (Zhang et al. 2018).
The Cannabis center of origin has been appraised by two different methods. Based on fossil pollen data, McPartland et al. (2019) proposed the northeastern Tibetan plateau, near Xīníng in Qīnghǎi Province. Based on haplotype data of extant plants, Zhang et al. (2018) offered the southeastern Tibetan plateau, in southeastern Tibet and adjacent northwestern Yúnnán.
C. sativa reached Europe by at least 6.3 mya (McPartland et al. 2018). Pleistocene
glaciations, increasing in amplitude 1 mya–800 kya (Ehlers and Gibbard 2007), likely drove vicariant divergence, splitting the European and Asian populations into discontinuous distributions. The two populations diverged due to genetic drift and environment-specific adaptations. The molecular clock analysis by McPartland (2018) estimated that C. sativa and C. indica diverged 1.05 mya, although the estimate was not robust, because the taxa differed at only one nucleotide site. Zhang et al. (2018) estimated the Cannabis crown age (divergence of haplogroups) was 2.24 mya.
European wild-types were assigned to the taxa C. sativa var. spontanea Vavilov (1922) and
C. sativa var. ruderalis Janischevsky (1924). Janischevsky also coined an alternative species rank, C. ruderalis, adding the caveat, I am inclined to consider it a well-marked variety.” The taxa by Vavilov and Janischevsky were based on the same population of wild-type plants growing near Saratov, Russia. At the time, both Vavilov and Janischevsky worked at Saratov.
“Cannabis exhibits marked phenotypic
plasticity (Darwin 1868) so it likely
evolved at higher latitudes or in
mountainous terrain”
