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Her mother’s laugh January 26th, 2020 by

In She Has Her Mother’s Laugh, Carl Zimmer, professor of science writing at Yale University, takes us on an enlightening and ambitious tour de force of genes and the history of their science. Zimmer loves a story, and he treats his readers to many along the way: for example, how the American plant breeder Luther Burbank, who had only a faint idea of genetics, but a keen eye for plants, bred everything from the Burbank potato to spineless cactus.

Zimmer’s stories weave in many ideas, but I want to focus on just two. First, many genetic traits are not governed by simple Mendelian genetics. Mendel, the ‘father’ of genetics, got lucky in his breeding experiments with peas, where easily observable traits like flower color and wrinkled seed coat are conveniently governed by single genes.

But there is no single gene for much of what we admire most. Tall people do have tall children, but there is no one gene for height. There are several thousand genes, each of which may add a hair’s breadth to your stature. Likewise, there is no smart gene, yet 84% of our 20,000 genes have some influence on our brain.

In agriculture we are seeing the same thing. For example, crop yield is shaped by a wide range of genes and there may not be any one gene that helps plants resist a specific disease.

A second of Zimmer’s lessons: nearly all genes are influenced by their environment. Healthy kids who eat nutritious food grow up to be taller than sick, hungry children.

In Europe, 30,000 years ago, hunter gatherer men were around 6 feet tall (183 cm). But early agriculture was not able to provide the protein and dietary diversity made possible by hunting and gathering. The first farmers were shorter than their ancestors, and from the dawn of agriculture until the 1700s the average European man stood at 5 feet 5 inches (165 cm). The move from agriculture into the industrial era was even more disastrous. At the end of the 18th century in England, 16-year-old boys from wealthy families were 9 inches (23 cm) taller than lads from poor homes. It wasn’t until the end of the 19th century that sewage systems had improved public sanitation (and people’s health) and the railroads began bringing fresh food long distances to cities. As urban people began to eat better, they got taller. Today many human populations are once again as tall as their ancestors were, 30,000 years ago.

So, there is no tall gene, yet good health and nutrition can help kids grow up to be as tall as their genes will allow. What is true for people is also true for plants and agriculture. Healthy soils, rich in organic matter, and well-managed water and a rich biodiversity of crops and wild plants and animals will help farmers to make the most of the genetic heritage of their plants and livestock.

Further reading

Zimmer, Carl 2018 She Has Her Mother’s Laugh: The Powers, Perversions and Potential of Heredity. New York: Dutton. 656 pp.

Related blog story

Read more about Luther Burbank and spineless cactus: Spineless cactus

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