What is plant domestication?
Domestication means people changed a wild plant over many generations so that it grows well in fields and is useful to us. It began about 10,000 years ago, when people first stayed in one place and farmed. Wheat and barley came from West Asia, rice from Asia, and maize from Mexico.
The plant does not choose this. The farmer does. This is called artificial selection: the farmer decides which plants make the next seeds.
Traits farmers selected
Early farmers kept seeds from plants that were easier or better to use. Slowly these cultivated traits became common:
- Seeds that stay on the plant. Wild seeds fall off (they shatter). Plants that held on to their seeds could be harvested, so their seeds were sown again.
- Bigger grains and fruits that give more food.
- Less bitterness or poison, so food tastes better and is safe.
- Even ripening and seeds that sprout together.
- Shorter, stronger stems that do not fall over.
Why does it work? Plants differ a little in their genes. Each season only the chosen plants pass on their genes, so the wanted gene versions become more common.
Loss of genetic diversity
When we keep seeds only from a few best plants, many gene versions are thrown away. This is loss of genetic diversity. Fields grow thousands of identical plants, called a monoculture.
The risk is simple. If one disease or pest can attack one plant, it can attack all of them. In Ireland in 1845 farmers grew almost one potato type, and a blight fungus ruined the crop. A mixed field is safer, because some plants usually resist.
How we protect diversity: keep landraces (old farmers' varieties) and wild relatives, and store seeds in seed banks, such as the one in Svalbard or the national gene bank in India.
Hybridisation and breeding
Hybridisation means crossing two different plants (parents) to get seeds with a mix of both. Breeders pick the parents so that one gives, for example, high yield and the other gives disease resistance. They grow many offspring and keep only the best, then repeat. This is plant breeding.
The first offspring of two pure lines is called an F1 hybrid. It is often stronger than both parents (hybrid vigour, or heterosis). Farmers usually buy fresh F1 seed each year, because seeds saved from the F1 plants give mixed results. The Green Revolution used hybrid and dwarf varieties of wheat and rice to raise yields. Read more in Plant breeding.
Genetic engineering of crops
In genetic engineering scientists cut one gene out of one organism and put it into a crop. The crop is then called a genetically modified (GM) or transgenic crop. Breeding mixes thousands of genes at once. Genetic engineering moves just one, and the gene can come from a different species.
Examples: Bt cotton has a gene from the soil bacterium Bacillus thuringiensis that makes a protein poisonous to the bollworm insect. It is grown in India. Golden rice carries genes to make beta-carotene (vitamin A). New tools like gene editing can change a gene in place.
People debate GM crops: they may need fewer pesticides, but we must test for safety to health and nature, and they should not reduce diversity further.
Try it
In the 3D, press Pick the biggest six times and watch the seed size and the number of varieties. Then press Send disease. Now reset, send disease at season 0, and compare. At home: take 20 beans, keep the 5 biggest, and compare their weight with the rest.
Key formulas and definitions
- Domestication = artificial selection over many generations
- Selection: only chosen plants give seeds for the next season
- Monoculture = one variety in a whole field (less diversity)
- Hybridisation: cross parents A × B to get F1 with traits of both
- Genetic engineering: one gene moved into a crop (transgenic / GM)
Worked examples
1. Why did plants that kept their seeds become the farmers' favourites?
A farmer can harvest seeds that stay on the plant. Seeds that fall off are lost. So seeds of "non-shattering" plants were sown again, and the trait became common.
2. A farmer has 200 plants and keeps seed from the biggest 10% only. How many parent plants is that?
10% of 200 = 0.10 × 200 = 20 parent plants.
3. Seeds weigh 2.0 g per 100 seeds. Each season of selection adds 10%. What is the weight after 3 seasons?
Each season multiplies by 1.1. After 3 seasons: 2.0 × 1.1 × 1.1 × 1.1 = 2.662 g, about 2.66 g.
4. A field has 5 varieties of equal share. A disease kills only variety 1. What share of the field is lost? What if the whole field is variety 1?
Mixed field: 1 of 5 = 20% lost. One-variety field: 100% lost. That is why diversity protects food.
5. Bt cotton kills bollworm. Is this hybridisation or genetic engineering? Why?
Genetic engineering. A single gene from a bacterium was inserted into cotton. Hybridisation only crosses plants of the same or very close species.
6. Out of 1000 old rice varieties, 80% were replaced by a few modern ones. How many remain? Name one way to save them.
1000 × 0.20 = 200 varieties remain. We can keep seeds in a seed bank and keep growing landraces.
Common mistakes
- Thinking the plant "wants" to get bigger seeds. The farmer chooses; the plant does not plan.
- Saying selection creates new genes. It only makes the already present gene versions more common (mutation makes new ones).
- Mixing up hybridisation and genetic engineering: crossing two plants versus moving one gene.
- Believing a uniform field is always better. It gives even harvests but is risky against disease.