Talk:Artificial selection

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Discussion for: Artificial selection • View • Links • Related changes

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Page scope

Artificial selection covers selection by people as a concept: deliberate and unconscious selection, the ways parents are chosen, the response over many generations and its side effects, what selection leaves in a genome, and how these have worked in hemp, drug-type plants and landraces. The method and arithmetic of one cycle of phenotypic selection belong to Mass selection, selection by survival and fertility to Natural selection, where and when the crop began to Domestication, the inheritance of chemotype to Genetic traits and how growers choose and keep seed in practice to Farmer selection and Landrace breeding. Definitions of a landrace belong to Landrace Cannabis.

Data verification

Record source conflicts, figures that differ between studies and sources not used here. Keep narrative content on the article.

Discussion

Sources

Darwin, On the Origin of Species (1859), pp. 11–12, 34–35, 83, 109, and The Variation of Animals and Plants under Domestication (1868), vol. 2, p. 193: methodical and unconscious selection, correlated change, selection on visible characters.
Gregory (2009), Evolution: Education and Outreach 2: 5–27, and Ross-Ibarra, Morrell and Gaut (2007), PNAS 104 (Suppl. 1): 8641–8648: Darwin's kinds of selection and their later names; Wallace's objection; early domestication by unconscious selection. Theunissen (2012), Journal of the History of Biology 45: 179–212: Darwin's use of pigeon breeders and his treatment of crossing and inbreeding.
Clarke and Merlin (2016), Critical Reviews in Plant Sciences 35: 293–327: the traits selected in cannabis; selection in hemp, drug cultivars and landraces; methods of breeding; loss of selected characters; the narrowing of hemp and drug gene pools.
Barcaccia and colleagues (2020), Frontiers in Plant Science 11: 573299, and Hurgobin and colleagues (2021), New Phytologist 230: 73–89: mass selection, cuttings, marker-assisted and genomic selection in cannabis.
Fehr, Principles of Cultivar Development, vol. 1 (1987; 1991 printing), p. 239; Beavis and colleagues (2023), "Selection response"; Felsenstein, Theoretical Evolutionary Genetics (December 2019), pp. 447–450: parental control; the breeder's equation; natural selection, drift and changing conditions as limits.
Laurie and colleagues (2004), Genetics 168: 2141–2155, and Moose, Dudley and Rocheford (2004), Trends in Plant Science 9: 358–364: the Illinois long-term selection lines.
Yamasaki and colleagues (2005), The Plant Cell 17: 2859–2872; Wright and colleagues (2005), Science 308: 1310–1314; Hufford and colleagues (2012), Nature Genetics 44: 808–811; Moyers, Morrell and McKay (2018), Journal of Heredity 109: 103–116: selection in crop genomes.
Ren and colleagues (2021), Science Advances 7: eabg2286; Woods and colleagues (2023), G3 13: jkac209; Grassa and colleagues (2021), New Phytologist 230: 1665–1679: selection scans and synthase genes in cannabis.
Bredemann, Schwanitz and von Sengbusch, Bulletin on Narcotics (1956), issue 3: 31–35, and Hennink (1994), Euphytica 78: 69–76: German and Dutch breeding of fibre hemp.
ElSohly and colleagues (2016), Biological Psychiatry 79: 613–619: THC in seized cannabis in the United States.
Zeven (1998), Euphytica 104: 127–139, and Clarke (1995), Journal of the International Hemp Association 2: 57, 60–65: human selection in landraces of crops generally and in the hemp of Tai'an.

Where the sources disagree

Human selection in landraces. Barcaccia and colleagues and Clarke and Merlin say landraces arose through mass selection. Clarke (1995) found little if any intentional selection in the Tai'an landrace and credits unconscious selection and natural factors, and Clarke is an author of both accounts. Zeven's review pulls two ways: p. 129 has "no, or only limited, human selection" and p. 137 has "a great influence". His review has no cannabis case.
Hemp before modern breeding. Bredemann and colleagues (1956) write that hemp in Europe outside Russia had not been changed much by breeding and call it a wild plant in cultivation. Clarke and Merlin describe earlier selection from local landraces and of 'Kentucky' hemp by about 1900. The first statement comes from breeders describing the problem their own programme addressed.
Synthase genes and other selected traits. Clarke and Merlin treat the loss of a working CBDA synthase as a step towards high THC in drug plants. Ren and colleagues agree on the loss and also argue, from exceptions in their sample and from the cultivar CBDRx, that synthase inheritance is independent of the other traits that separate hemp from drug types.
The term. Gregory notes the argument of Heiser (1988) and Zohary (2004) that present use of deliberate or methodical selection differs from Darwin's. He holds that it is in essence the same process, in which people choose individuals to preserve traits of interest.
A page number. Gregory gives p. 153 for Darwin's 1868 definitions. In the first edition they are on p. 193 of volume 2.

How far the evidence goes

The sources give no measured selection differential or response for a cannabis landrace. Zeven's "little has been recorded" concerns crops in general.
The rise in fibre content from about 12 to about 24 per cent is the breeders' own report in 1956. The 1956 paper gives no trial data for it and states that the strain yielded poorly.
The THC series covers plant material seized in the United States. Its authors report a shift from regular marijuana to sinsemilla. It does not divide the rise between genetic change and change in cultivation.
Genome scans name candidate genes. The functions given for the genes in Woods and colleagues come from their closest matches in Arabidopsis, and Ren and colleagues state that their synthase pattern would need confirming with phenotypic or expression data.
Clarke and Merlin attribute the true males and females in third-generation monoecious crops to inbreeding and drift without selection, and cite de Meijer (1995) for the decline of monoecious cultivars.

Terms

Methodical selection is Darwin's word for what later writers call deliberate, conscious or intentional selection. Unconscious selection is also called automatic or unintentional.
Selective breeding is used here as another name for artificial selection.
Narrow-leaflet and broad-leaflet drug plants are the groups of Clarke and Merlin (NLD and BLD).
Improvement in the maize genome studies means breeding after domestication.