How Did Farmers Make Our Crops?

Put a wild plant beside the crop that came from it and the difference is startling. The best-known pair is maize and its wild ancestor, a Mexican grass called teosinte. A teosinte ear is a few centimeters long, with only about 5 to 12 seeds, each sealed in a stony case that a person can hardly bite through. When ripe, the ear breaks apart and the seeds scatter. A maize cob is many times longer, with hundreds of soft kernels in rows, held so tightly that they never fall off by themselves.

The same story is told by almost every crop. Look at the changes farmers made, crop after crop:

A wild plant…	Its crop…	Why the farmer wanted it
drops its seeds as they ripen	holds them until it is cut	the harvest waits for the farmer
has small seeds	has big seeds or grain	more food for the same work
has seeds that wait years before they sprout	has seeds that all sprout at once when sown	the whole field grows and ripens together
often has hard cases, bitter tastes or spines	is softer, less bitter, easier to eat	food that is easy to cook and eat
ripens a few seeds at a time	ripens all at once	one harvest instead of many

Turning a wild plant or animal into one that lives with people and depends on them is called domestication. Wheat and barley were domesticated in western Asia, maize in Mexico, potatoes in the Andes of South America. Asian rice, the rice of Nepal, came from a wild rice of southern and eastern Asia. One of the clearest records of the farm kind taking over comes from the Yangtze valley of China, about 7,000 years ago; rice was gathered and sown there for a long time before that.

Copies and mixes

You learned in Grade 8 that gardeners keep a good plant by artificial vegetative propagation: a cutting, a layer, a gootee, a graft or tissue culture grows into a copy of the parent Grade 8: Grade 8: Artificial vegetative propagation. A copy has exactly the parent’s genes, so it can keep a good variety, but it can never make a new one. New varieties come from seeds, and every seed is a new mix of genes from two parents (Why Do You Look Like Your Parents, but Not Exactly?). Most of what farmers did to make crops, they did by choosing which seeds to sow.

How could farmers who knew nothing about genes have turned shattering wild rice into rice that holds its grain? The surprising answer is that they probably didn’t mean to.

In a big field of wild rice, a few plants now and then have a small change, a mutation, in one of the genes that make the grain break off (When a recipe changes). In rice, scientists have found that a change of a single letter in one gene, called sh4, is enough to make the grain hold on much more tightly. In the wild, such a plant is a failure: its grain doesn’t fall to the ground, so it doesn’t sow itself.

Now think of the first farmers. They cut the ripe rice with a sickle, carried it home, and next year sowed some of what they had harvested. Which grain was in the harvest? Hardly any from the plants that had already dropped theirs, and all of it from the rare plants that held on. Without meaning to, the farmers were choosing those plants to be the parents of the next crop.

The ratio is multiplied by 1.43 again next year, and the year after: the same shortcut you met with snow leopards (A shortcut: the ratio). Starting from 1 : 99, it reaches about 1 : 1 after 13 years (1.43 multiplied by itself 13 times is about 104), and nearly every plant holds its grain within about 25 years.

In 1990 two British archaeobotanists, Gordon Hillman and Stuart Davies, worked this out for wild wheat and barley, using measurements from their own trials of harvesting wild wheats. Their answer was that the farm kind could take over in as little as 20 to 30 years, and within about 200, if farmers cut their crop when it was nearly ripe and sowed it in new ground each year.

Once people began farming, they also chose on purpose. Every farmer in Nepal knows the rule: keep the best for seed. A farmer who saves seed only from the plants with the longest ears, the biggest grains or the sweetest fruit, and eats the rest, is changing the crop. Choosing which plants or animals become parents, so that the next generation has more of a quality people want, is selective breeding, also called artificial selection: people do the selecting, instead of nature. In Grade 10 you’ll meet its methods and their names Grade 10: Grade 10: Selective breeding.

Selective breeding has made astonishing differences: that Grade 10 section shows how one wild plant became cabbage, cauliflower, broccoli, kohlrabi and kale. And it works on animals too: raising and breeding farm animals is called animal husbandry, and choosing which animals become parents is a big part of it.

Genes or soil?

There is a catch, and you know it from Why Do Two Plants from the Same Field Grow So Differently?: a plant may be big because of its genes, or because it had a good patch of soil, more light or more water. Seed carries the genes, not the soil. If a farmer keeps seed from a plant that was big only because it grew near the compost heap, its seed will grow ordinary plants.

So when the chosen plants are better than average, only part of their advantage is passed on: the part that came from their genes. Breeders have a rule for it, called the breeder’s rule:

$$\text{gain in the next crop} = (\text{share of the differences that comes from genes}) \times (\text{how much better the chosen parents are})$$

The share of the differences between plants that comes from their genes is called heritability. It is a number from 0 to 1. If it is 0, all the differences are from the soil and the weather, and choosing does nothing; if it is 1, they are all from genes, and the next crop is as good as the chosen parents.

High in Karnali, in the fields of Jumla, farmers grow rice at about 3,000 m above sea level, among the highest rice fields in the world. They grow a red rice called Jumli Marshi, which their families have kept for hundreds of years by saving its seed, because it survives cold nights that kill other rice.

Crossing two varieties to bring a quality from one into the other is crossbreeding, and checking seedlings’ DNA to choose the parents is marker-assisted breeding. It is still selective breeding, but with a new tool: breeders can now see a gene before they can see the trait.

In the 1950s and 1960s, many people feared that India, Pakistan and other poor countries would soon face famine: their populations were growing faster than their harvests. Feeding wheat more fertilizer didn’t help much, because the tall old wheats grew heavy heads and then fell over in the wind and rain, a problem called lodging.

The new varieties saved many millions of people from hunger. But they came with costs that are still being argued about:

• They gave their big harvests only with plenty of fertilizer, water and pesticides, which cost money, can pollute rivers and soils, and helped richer farmers more than poorer ones.
• Farmers everywhere grew the same few varieties, and stopped growing thousands of local ones. A field of plants with the same genes can be wiped out by one new disease, as happened to Ireland’s potatoes in 1845–1849, when about a million people died, and to the world’s favorite banana in the 1950s (The banana that disappeared).

The old local varieties carry genes that may be needed one day: for a new disease, a hotter climate, a drought. So countries now keep their seeds in gene banks, cold stores where seeds stay alive for decades. Nepal’s national gene bank, at Khumaltar in Lalitpur, opened in 2010 and keeps more than 10,000 samples of the seeds of Nepal’s crops and their wild relatives. A spare copy of the seeds of gene banks from all over the world is kept deep in a frozen mountain in Svalbard, near the North Pole: about 1.38 million samples, as of the end of 2025.

Selective breeding can only choose among the genes a plant or animal already has, or can get from a relative it can breed with. A rice plant can’t breed with a bacterium. Since the 1970s, scientists have been able to move a gene from one living thing into another directly, in the laboratory. This is genetic engineering, also called genetic modification; a living thing changed this way is a genetically modified organism, or GMO.

It works because every living thing uses the same kind of DNA, written in the same four letters, and reads it the same way. A gene from a bacterium, put into a plant cell, is read by the plant’s cell just as it would be in the bacterium, and the plant makes the bacterium’s protein. In Grade 10 you’ll meet genetic engineering again, with more examples Grade 10: Grade 10: Genetic technology.

Insulin from bacteria

People with type 1 diabetes need injections of insulin, a protein that controls the sugar in their blood. Until the 1980s, it came from the pancreases of cattle and pigs from slaughterhouses. In 1978 scientists put the human insulin gene into bacteria, and the bacteria made human insulin. In 1982 it became the first medicine made by genetic engineering to be sold. Today most insulin is made by genetically modified bacteria or yeast, in big steel tanks.

Bt cotton

A soil bacterium called Bacillus thuringiensis, Bt for short, makes a protein that kills certain caterpillars, such as the bollworms that eat cotton bolls, but is harmless to people, birds and most other animals. Organic farmers have sprayed Bt for decades. Scientists took the gene for this protein and put it into cotton.

Step 3 is the tissue culture of Grade 8: a whole plant grown from a few cells. Without it, there would be no way to turn one changed cell into a plant.

In India the gene was then crossed into Indian cottons by ordinary breeding: the two kinds of technology work together. India began growing Bt cotton in 2002, and within about ten years it was over 90% of India’s cotton. Farmers sprayed much less insecticide against bollworms, and harvests rose. But one bollworm, the pink bollworm, evolved resistance: by about 2010 there were pink bollworms in India that Bt cotton no longer killed. In a field where every plant makes the poison, the rare caterpillar that can survive it has every advantage: natural selection, exactly as in How Do Snow Leopards Come to Fit the Mountains?

Golden Rice

Lack of vitamin A blinds hundreds of thousands of young children every year in poor countries, and weakens their resistance to disease. Golden Rice was given genes, from maize and from a bacterium, that make the grain store beta-carotene, the orange substance in carrots, which the body turns into vitamin A. It took more than 20 years of testing before the Philippines, in 2021, became the first country to approve it for growing. In 2024, a court in the Philippines stopped it again, after a case brought by farmers’ groups and campaigners who argued its safety hadn’t been proved.

Gene editing

Since 2012 there has been a newer tool, CRISPR. Bacteria use it to cut up the DNA of viruses that attack them; Emmanuelle Charpentier and Jennifer Doudna showed how to aim it at any DNA we choose, and won the Nobel Prize in Chemistry in 2020 for it. It works like a find-and-replace: it can be sent to one exact place in a cell’s DNA and cut it there, so that scientists can switch a gene off or change a single letter. This is gene editing. Often nothing from another species is added: the change could have happened by itself as a mutation, only faster and in exactly the right place.

What people argue about

Genetic engineering is one of the most argued-about technologies in the world. The arguments are of different kinds, and it helps to keep them apart:

• Is the food safe to eat? Every GM crop is tested before it is approved. Large reviews by scientific bodies, such as the US National Academies of Sciences in 2016, found no evidence that the approved GM crops were less safe to eat than ordinary crops. That is a conclusion about the crops tested, not a promise about every future one, which is why each new one is tested.
• What does it do to the environment? Bt crops cut insecticide spraying, but pests can evolve resistance. Genes can spread by pollen to wild relatives or to neighbors’ fields.
• Who owns the seeds? A new variety can be patented, and farmers may have to buy new seed every year instead of saving their own. That is a question about money and law, not about biology.
• Who decides? Each country makes its own rules, and they differ a lot, as Golden Rice in the Philippines shows.

Some diseases come from a harmful version of one gene. One of them is sickle-cell disease: the gene for hemoglobin, the protein that carries oxygen in red blood cells, has a one-letter change that makes the red cells bend into stiff sickle shapes, which block small blood vessels and cause terrible pain. In Nepal it is found mostly in the western Terai.

Treating a disease by changing the genes in a patient’s own cells is gene therapy. The first was given in 1990, to a four-year-old girl in the USA, Ashanti DeSilva, whose body couldn’t fight infections because of one faulty gene. In 2023 Britain and then the USA approved the first gene-editing treatment, for sickle-cell disease: doctors take blood-making cells from the patient’s bone marrow, use CRISPR to break a genetic switch that, after birth, turns off the gene for the kind of hemoglobin a baby makes before birth. With the switch broken, that gene comes back on, and its hemoglobin isn’t affected by the disease. Then the cells are put back. Most patients treated in the trials stopped having pain crises. As of 2025, it costs about two million US dollars per patient.

Gene therapy changes cells of the body, such as blood cells, not eggs or sperm, so the change is not passed on to the patient’s children. Changing the genes of an embryo would change every cell of the person, including their eggs or sperm, and so every generation after them. In 2018 a Chinese scientist, He Jiankui, announced that he had done this to twin girls before they were born. Scientists around the world condemned it as unsafe and wrong, and he was sent to prison. Many countries forbid it by law.

Each of these technologies rests on discoveries, and many of the discoveries came from new tools:

When	What happened
about 11,000 years ago	farmers in several parts of the world begin to sow seeds, and crops begin to change
1866	Gregor Mendel publishes his experiments with peas: traits are passed on as separate units, later called genes
1900s–1930s	breeders begin to use Mendel’s laws to plan crosses, and make the first hybrid maize
1953	Rosalind Franklin’s X-ray photographs of DNA help James Watson and Francis Crick find its structure, the double helix
1973	Herbert Boyer and Stanley Cohen put a gene from one living thing into a bacterium, using enzymes from bacteria that cut DNA at exact places: one of the first feats of genetic engineering
1982	human insulin made by bacteria goes on sale
1990	the first gene therapy
1996	the first GM crops grown widely, in the USA
2003	the whole human genome, all 3 billion letters of our DNA, is read
2012	CRISPR gene editing
2023	the first gene-editing treatment approved, for sickle-cell disease

Notice how the tools come first. Nobody could find DNA’s shape until X-ray photographs could show how the atoms in its fibers were arranged. Nobody could move a gene until enzymes were found that cut DNA at exact places. And CRISPR was found by scientists studying how bacteria fight off viruses: they were not looking for a tool at all.

You will hear many claims about crops, seeds and genes: on the news, from seed sellers, from neighbors. “Hybrid seed gives double the harvest.” “GM food causes cancer.” “Our old rice is healthier.” Some are true, some partly true, some false. Here is how scientists check a claim, and how you can.

1. Who says it, and how would they know? A research institute or university that measured something knows more than someone repeating what they heard.
2. Do they gain from your believing it? A company selling seed, or a group raising money against GM food, may be right, but check with someone who gains nothing.
3. What is the evidence? Look for measurements: how many fields, how many years, compared with what.
4. Do other reliable sources agree? One study can be wrong. When national science academies, the FAO (the United Nations’ farming organization) and many studies say the same, it is probably true.
5. How old is it? Rules, prices and the facts about a new variety change quickly. Look for the date.

• How Do Snow Leopards Come to Fit the Mountains? The same kind of selection with nobody choosing at all: how small differences in survival shape animals to where they live.
• Why Do You Look Like Your Parents, but Not Exactly? The genes that breeders choose among: how they pass from parents to young, and why every seed is a new mix.
• Why Do Two Plants from the Same Field Grow So Differently? Seed and soil: how genes and surroundings together decide how a plant grows.