Welcome to Quantum Magazine's podcast.

Each episode we bring you stories about developments in science and mathematics.

I'm Susan Vallet.

The developing embryo is a finely tuned machine.

Its cells know what to do and when to do it. They know to grow or shrink,

to divide, or lie dormant, to come together into a beating heart or hurtle through the bloodstream

in search of a distant invader. And they know how to do all that without a central

command station or an objective map of their surroundings to guide them.

Instead, cells are left to devise their own strategies for calculating precisely where to go and what to become.

Those calculations depend on a variety of signals, some of which have long been established as obviously important, chemical and electrical gradients,

the activity of gene networks, patterns of overlap between spreading fields of molecules.

But recently, experts have also started to pay attention to another often overlooked set of factors,

physical constraints, like size.

In work published last summer in nature physics, a team of researchers looked at the early

development of the roundworm, xenorobditis elegans, a type of nematode in soil.

They found a mechanism based on the size of embryonic cells helps to determine the type of nematode in soil. They found a mechanism based on the size of embryonic cells

helps to determine the type of mature tissues they will eventually produce. The scientists examined

the biochemical process that triggers cells to divide either asymmetrically or symmetrically.

They discovered that size was the ruling element,

meaning the size of the cells dictated the pattern that led to one kind of division or another,

and ultimately to one kind of lineage or another. Martin Howard is a computational biologist

at the John Innes Center in England. He didn't participate in the study.

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