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Building Bodies

From a single cell, a human embryo grows into a collection of tens of trillions of highly integrated, highly specialized functionaries. How does it do it?

Biologists have long been obsessed, and we have become so, too. The result is this special report on Building Bodies. It includes a taste of the captivating things that scientists have learned about the principles and strategies that go into sculpting animal and plant forms — and the many puzzles remaining.

In this report, we look at unseen forces that push and pull cells from a naïve state to sophistication. We examine the body as a bag of branching tubes and ask how those structures are fabricated. And we lay out simple-seeming questions, such as: How does the embryo know top from bottom, or left from right? How does a spleen or a lung know how big it should grow to be? There’s an elegance to the answers that scientists are unearthing.

There are many common threads in the solutions that creatures like worms, flies, mice and humans have come up with to solve such problems — and through the decades, research in one has informed understanding of another. But our report also examines some stark differences. We look at the growing rules for trees, for example: Out of necessity, since they can’t move around, their shapes are far more plastic than animals’. And with envy we delve into the prodigious ability of salamanders to regrow lost limbs. Maybe, through learning how they do it, we might one day duplicate the process in people.

Read on, enjoy — and let us know what you think on Twitter, Facebook and by emailing the editors. And if you want to track what Knowable is up to each week, an easy way to do so is to sign up for our newsletter.

— Rosie Mestel and the Knowable Magazine team

Bent into shape: The rules of tree form

How do trees find their sense of direction as they grow? Researchers are getting to the root — and the branches — of how the grandest of plants develop.

Growing a body, one tiny tug at a time

For decades, genetics and biochemistry have formed the bedrock of developmental biology. But it turns out that physical forces — the way cells push, pull and squeeze each other — play a huge role, too.

Plumbing 101: Building the body’s tubes and branches

Lungs, blood vessels, kidneys and more: Our bodies are full of branching pipes. Their development follows a handful of basic principles.

Regeneration: The amphibian’s opus

Certain salamanders can regrow lost body parts. How do they do it? And could people someday do the same?

How do bodies position arms, legs, wings and organs?

FIVE BIG QUESTIONS: Embryos use a ruler, of sorts, so they can create the right structures at the right spots from head to tail.

How do bodies map out left and right?

FIVE BIG QUESTIONS: Early in development, an embryo must “break symmetry” to position organs and other parts correctly.

How do body parts grow to their right sizes?

FIVE BIG QUESTIONS: Some cells seem to know what to do. Others apparently take their cues from outside. But really, “We don’t get it.”

How does the embryo make all its parts at just the right moments?

FIVE BIG QUESTIONS: If events weren’t properly timed, pandemonium would ensue. Researchers are ferreting out the internal clocks that control developmental sequence and scheduling.

Will we ever fully know how a body gets built?

FIVE BIG QUESTIONS: Research has yielded a parts list of the genes and cell types involved in development. Now it’s time for the computationally intensive task of figuring out how they interact to form a living being.