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What Domestication Actually Changed: The 40-Genome Study

By Matt Goren2026-09-05 10:30:00 -04002 min read

Reading Domestication Directly

Most domesticated species cannot be studied this way, because their wild ancestor is extinct or disputed. The silkworm can, because Bombyx mandarina is still alive. So researchers did the obvious thing: sequenced both and compared them.

The Study

40 genomes — 29 domesticated lines and 11 wild — each sequenced to roughly threefold coverage, producing a variation map covering 99.88% of the genome. That map is what allows the question to be asked precisely: which parts of this animal did people change?

What They Found

354 candidate genes carrying signals of selection. Not scattered at random, but concentrated where you would expect if you knew what farmers had been selecting for. Enriched expression showed up in:

the silk gland — the organ being harvested
the midgut — how much leaf becomes animal
the testis — reproduction, which in a farmed animal means throughput

Among them were transcription factors that regulate the silk protein genes themselves — not changes to silk, but changes to the switches controlling how much silk gets made. Five thousand years of picking the best cocoons appears to have worked partly by turning up the volume rather than rewriting the song.

Domesticated Once

The other finding is the cleaner one. Silkworms were probably domesticated a single time, from one large founding population — unlike several other domesticated animals, where the record shows the same thing happening independently in different places.

One event, one population, and everything since.

A Note on the Date

You will see the age of silkworm domestication given as "at least 5,000 years" and as "over 10,000 years" in different sources, and both appear in reputable work. We have used the conservative figure elsewhere on this site and it is worth saying plainly that the range is genuinely contested rather than quietly picking whichever number reads better.