A classic genetic model of domestication predicts a bottleneck.
A small subset of a wild population is selected.
Those individuals become the founders of the crop.
Genetic diversity collapses.
Strong selection then fixes important domestication alleles.
This certainly can happen.
But the review argues that it is not an adequate general model for early plant domestication.
Archaeology predicts weak selection
If domestication took thousands of generations, selection could have been relatively weak.
Under weak selection, more individuals remain within the reproducing population.
That preserves diversity.
Genomes reveal multiple contributors
Ancient and modern genomic data increasingly indicate that several crops incorporated genetic material from multiple wild populations.
Barley, emmer, maize and bananas all provide examples of complex histories.
Instead of:
wild population → bottleneck → crop,
the history may resemble:
multiple wild populations ↔ cultivated populations ↔ migration ↔ hybridisation → crop metapopulation.
Gene flow can rescue crops
One of the most important examples discussed in the paper concerns sorghum.
Ancient sorghum genomes from Nubia suggest that genetic load increased through time.
Isolation can allow harmful variation to accumulate or useful diversity to disappear.
But contact with other sorghum populations can introduce new variation.
This process is known as genomic rescue.
Hybridisation, far from contaminating a pure crop lineage, can therefore restore resilience.
Purity may be the wrong metaphor
Modern breeding often emphasises uniformity.
Ancient domestication frequently appears to have benefited from mixture.
The history of successful crops may therefore be partly a history of repeatedly reconnecting populations.
Agricultural resilience sometimes grows from genetic messiness.
That lesson has obvious consequences for modern crop conservation.
Wild relatives, traditional landraces and geographically isolated crop populations should not be viewed simply as museum pieces.
They represent reservoirs of evolutionary options.
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Further reading: This post is inspired by and draws on Dorian Q. Fuller, Tim Denham, and Robin Allaby, “Plant domestication and agricultural ecologies,” Current Biology 33, no. 11 (2023): R636–R649, doi:10.1016/j.cub.2023.04.038. Read the original article in Current Biology
For a classic and highly readable perspective on why plant domestication arose in some regions but not others, see Jared Diamond, Chapter 8, “Apples or Indians: Why Did Peoples of Some Regions Fail to Domesticate Plants?”, in Guns, Germs, and Steel: The Fates of Human Societies (W. W. Norton, 1997), pp. 131–156. Read “Apples or Indians” View Guns, Germs, and Steel on Google Books
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