For thousands of years human gardeners and farmers have performed feats of "genetic engineering," transforming the seeds of wild grasses into corn, oats, and wheat, wolves into dogs, and aurochs into modern cattle.
While it is impossible to be certain about the origin of modern maize or corn, there is evidence that modern corn with its kernal-filled ears was engineered by humans from a grass called teosinte, a many stalked grass that grows to over a man's height, and which may be found in Mexico along streams and on hillsides, and even occasionally as a weed in farm fields. (Anderson, 2017)
Despite the teosinte plant's impressive size, its seeds are much more modest; a teosinate ear has perhaps 5 to 12 kernals, each locked in a very hard casing called a glume.
The nearly sturdy glumes protect each of the seeds from the digestive systems of the birds and mammals that may ingest them and ensure that the seed's DNA will remain intact so the seed can produce a new teosinte plant.
Genetic evidence indicates that the teosinte plant and humans came together around 10,000 years ago when perhaps an ancient forager found a variety of the teosinte whose glumes were only partly formed, exposing the seeds and making them available to the forager's collecting bag. (Standage, 2009)
If humans had not exploited teosinte as a food source, the teosinte plants with the malformed glume would perhaps have become extinct because the seeds would have been digested instead of becoming a new plant.
Perhaps because humans recognized the plant's value, the malformed variety of teosinte may have become the ancestor of modern corn.
Modern corn with its large, many-kerneled ear, and its husk, like its ancestor remains dependent on humans for its survival. If humans disappeared, modern corn would also disappear because the kernel-crowded ear needs to be de-husked and the kernels separated so the seeds can be spaced so that each will have sufficient soil, water, and sunlight to grow.
We know that the domestication took place in southern Mexico and that the domestication happened numerous times because we have inherited many different varieties of corn. (Anderson, 2017)
While we have no historical account of how teosinte or any other plant or animal was domesticated, the work of a 1950s era Soviet scientist named Dimitri Belyaev worked to understand the process that transformed wolves into dogs.
Belyaev's laboratory was in Siberia and was affiliated with the fur industry, specifically, the many farmers who raised arctic foxes for their fur. "How," Belyaev asked himself, "did an animal that started out as a bloodthirsty predator become one that now wants nothing more than a nice belly rub and the chance to gaze adoringly at a member of another species?" (Zuk, 2017)
Since he had access to a large captive population of wild foxes, Belyaev began an experiment described in the book How to Take a Fox (And Build a Dog). Belyaev "and his colleagues took the silver foxes and made them into friendly house pets. It was a deceptively simple process: Take the puppies only from the friendliest foxes, breed them, repeat." The current (56th) generation of foxes, now "run towards people, jump on the bed, nuzzle one another as well as their human caretakers." Further the current generation foxes even look more dog-like, "with floppy ears, wagging tails and piebald fur." (Zuk, 2017)
Gregor Mendel had identified the "unit of heredity" (later named "gene"). But a name doesn't tell you what the thing does. The question: "What makes some fox kits (puppies) have floppy ears?" is another way of asking "How does a 'gene' create a physical trait?"
A gene is an information container. Its information is a message containing the directions for assembling specific proteins out of the 20 amino acids that appear in genetic code. A protein performs a function.
Hemoglobin is a protein composed of 477 combinations of the 20 amino acids used by living things. The function of hemoglobin is to transport oxygen to every cell in the body and return with waste CO2. (Mukherjee, 2016, p. 163)
In the teosinte plant the gene TGA1 creates the protein that influences the building of the glume. A mutation of this gene resulted in the creation of more open glume. (Preston, Wang, Kursel, Doebley, & Kellogg, 2012)
When humans pick the nicest fox puppy or the teosinte plant that has the seeds that are easiest to access to breed, they are actually selecting the gene or combination of genes that gives them what they want. As they do this, they increase the number of teosinte plants or foxes with the desired genes.
Without human intervention, it is the plant or animal's environment that does the selecting. As Darwin puts it, "if we wished in imagination to give the plant the power of increasing in numbers, we should have to give it some advantage over its competitors, or over the animals which preyed upon it." (Darwin, 2004a, p. 73)
Andersson, L. (2017). What is teosinte.
Darwin, C. (2004a). The Origin of Species by Means of Natural Selection. New York: Barnes & Noble Classics.
Darwin, C. (2004b). The Origin of Species by Means of Natural Selection. New York: Barnes & Noble.
Mukherjee, S. (2016). The Gene: An Intimate History. New York: Simon & Schuster.
Preston, J. C., Wang, H., Kursel, L., Doebley, J., & Kellogg, E. A. (2012). The role of teosinte glume architecture (tga1) in coordinated regulation and evolution of grass glumes and inflorescence axes. New Phytologist, 193(1), 204-215. doi:10.1111/j.1469-8137.2011.03908.x
Standage, T. (2009). The Man-Made Nature of Maize. In An Edible History of Humanity. Bloomsbury USA.
Zuk, M. (2017c). How Do You Make a Fox Your Friend? Fast-Forward Evolution. New York Times.
Dr. John Holton
Dr. John Holton joined the S²TEM Centers SC in July of 2013, as a research associate with an emphasis on the STEM literature including state and local STEM plans from around the nation.