How did they domesticate corn


How did they domesticate corn

In: Biology

They took seeds from wild corn and stuck them in the ground to grow. The biggest and best looking corn that grew was planted again. The cycle repeats with the biggest and best corn being planted each time. Over time the wild corn turned into the corn we have today.

Take seeds plant them in the ground, water them and wait to harvest them, the plants that then produce the best corn you save for planting next year, repeat, repeat, repeat.

Domestication, or artificial selection, happens when humans evaluate several individual organisms, which naturally have some variation between each other, and facilitate the creation of offspring from organisms that have traits deemed most desirable.

For instance, out of several dogs of each sex, you might choose to keep them all apart except for the largest male and largest female which you allow to mate, in hopes of creating a new generation of dogs that are on average larger than the previous generation.

We call the traits we selectively breed for “phenotypes,” and they are physically observable in some way – size, shape, color, number of leaves, sweetness of fruit, etc.

For organisms like corn, these phenotypes are the result of differences in cells – how they clump together to form structures of the plant like stems and leaves, how they store energy, how fast they grow, etc.

Going further, these differences in cells are the result of differences in molecules inside of the cells called proteins. More of less of a particular protein, or different kinds of protein, or proteins being made at different times or in different parts of the cell.

Finally, these differences in proteins are the result of differences in the genome, or DNA, of the organism. We call this the “genotype.”

Because there are so many layers of biological mechanisms at work here – at the DNA, protein, and cellular level – things can get a little complicated. You want a generation of bigger dogs, so you breed two big dogs together…but sometimes the resulting offspring are smaller than their parents! What happened? The answer is that there is not always an intuitive, 1-to-1 correlation between the phenotypes of the parents (the physical traits you see) and their genotypes (their DNA).

During sexual reproduction, the DNA from the mother and father combine a bit like two decks of playing cards getting shuffled together, with half the cards being discarded and the rest of the cards in a different order than the deck of either parent.

But DNA is more complex than just getting dealt either a “Large” or “Small” gene. Think of all the ways an organism has to be different in order to be larger or smaller. A dog will need to make each one of its bones proportionately larger, which also means it needs more muscles to move them and more blood vessels to support the tissue. In plants, extra fruits or seeds can occur when entire chromosomes (containing hundreds of thousands of genes) to literally duplicate! So, anywhere from one to hundreds of thousands of genes can be involved for any one single “trait” that a human observes.

Until a few decades ago with the discovery of molecular cloning techniques, humans had no way to change these genes on our own. So how could humans thousands of years ago have changed a plant from one form into another? The same way that natural selection does when humans aren’t involved: the combination of VARIATION and SELECTIVE PRESSURE.

VARIATION comes mostly from that random shuffling of the deck during sexual reproduction, but also happens because of things like mutations that happen when cells make mistakes copying their DNA, or from transduction events where retroviruses infect cells and permenantly insert their DNA into the host cell DNA. This means that with the exception of twins with the same DNA, no two organisms are exactly alike.

SELECTIVE PRESSURE happens when some of these organisms are better able to contribute their own DNA to the next generation than other organisms. In natural selection, this could be because a particular squirrel is better at remembering where she put her nuts than a different squirrel, and so is able to produce healthier offspring. In artificial selection, this could be because humans control which organisms get to pass their DNA onto the next generation, and humans want the next generation of squirrels to have fluffier tails, etc.

So to summarize: Humans intentionally mated together plants that gave them the most value – perhaps based on things like size, number of kernels, nutritional value of the kernels, etc. Sometimes the resulting generation of plants had a phenotype that was of more value to humans the the phenotypes of previous generations, and sometimes there honestly wasn’t too much of a difference. This was because the genotypes – the genes, the DNA – of the plants were not visible to them. In the book chapter I like below (“Tracking Footprints…”) you can read how scientists are debating what genes humans ended up selecting for. There is a lot of technical jargon, but from reading this you should be able to follow along and I encourage you to try reading it, even if only 20 or 30% of it makes sense right now.

Honestly, with literature like this, like 25% of it is intelligible to an intelligent person with a high school scientific background, 50% to someone with a few more years of study, 75% to a grad student in a related discipline, 95% to a scholar in that field, and only 99% if you’re the one who wrote the article 😉

Science always looks so overwhelming/overwhelming and intimidating t first, but always remember that you do not need to be brilliant to understand science. It is all logical, and will make sense if you think about it long enough. If you don’t understand something in science, it’s not because you’re stupid, it’s because it hasn’t been communicated to you properly. Fancy acronyms and formulas aren’t inherently esoteric and only understandable by geniuses – all of science, ALL of it, can be learned. All of it. And don’t let anyone hold their scientific knowledge over you like them holding that piece of information makes them better or smarter than you. It does not. It just means they uploaded that data file, and you haven’t yet.

The only thing that makes you “good” at science that you can’t learn is curiosity – but you’ve already got that! <3 Happy learning my friend. Genetics is a fascinating subject and I really do hope you keep exploring!!

Chapter Six, “Tracking Footprints of Maize Domestication and Evidence for a Massive Selective Sweep on Chromosome 10.” Feng Tian, Natalie M. Stevens, Edward S. Buckler. National Academy of Sciences (US); Avise JC, Ayala FJ, editors. In the Light of Evolution: Volume III: Two Centuries of Darwin. Washington (DC): National Academies Press (US); 2009. 3, Genetics and Ecological Speciation.

Chapter One, “An Edible History of Humanity.” Tom Standage. Walker & Company, 2009.