They say that the secret of good parenting is knowing when to let go. Yet I couldn't help trembling that morning, as she came to take my little ones away.

“Do you mind?” she grunted, sniffing their smooth skin.

“Not at all,” I lied. She was about to help herself to the first of my babies, when a gust of wind forced me to drop another. It just missed her snout. “Sorry.”

“No worries. Can't defeat the law of gravity. One of your family's contributions, if I'm not mistaken.”

She must have been referring to Malia, my 17th century English relative. Malia had dropped one of her little ones while a certain Isaac Newton had been sitting in her shade. That's what gave him the idea of gravity. “I'm surprised you know about it,” I said.

“History of science is a hobby of mine. You know my ancestor Susumu helped discover a fundamental force too, as important as gravity in its own way.”

I found that hard to believe but wanted to keep her talking in the hope she might forget her quarry. “Really? Do tell me more.”

“Susumu's moment of fame came in 1748, about 80 years after your Malia inspired Newton. A French physicist, a certain Jean-Antoine Nollet, was looking for something to seal a container filled with alcohol. Susumu had donated his bladder to science, so Nollet used that for the job. After standing the sealed container in water for 6 hours, Nollet noticed that Susumu's bladder had bulged out. He pricked a hole in it and saw liquid spurt high into the air. The container had clearly become pressurised. That's how Nollet and Susumu discovered the new force.”

“Sounds more like stumbling on a quirk than a great discovery,” I couldn't help pointing out.

“The next century,” my visitor continued, “another Frenchman, Henri Dutrochet, working in his chateau in Touraine, put a snail sperm sac in water and noticed the contents extrude, as if pushed out by a piston. Then he filled some chicken gut with milk and showed it took up water when submerged, concluding that the same force was at play. He called it endosmosis, which means ‘inward impulse’. He proposed it was an essential force for life and presented his findings at the French Academy of Sciences on Monday 30th October 1826. After he'd finished his reading, François Magendie, an authority on absorption, rose up to challenge him. How could an amateur have discovered a new force? The results were clearly explained by the well-known phenomenon of capillarity. History proved Magendie wrong and vindicated Dutrochet.”

My visitor paused to devour one of my little ones. “Delicious, if I may say so.”

My distress turned to anger. “I don't see how your piddling force can be compared to gravity! Without gravity none of us would be here!”

She must have guessed the cause of my outburst. “Don't worry, your babies will come out beautifully anointed.” She proceeded to guzzle another. “The question is…,” loud burp, “what is the expansive force that will drive their growth? Not gravity. Gravity compresses rather than expands. It can help orient growth but can't drive it. No, the growth force is the one discovered by Susumu, Nollet and Dutrochet: osmosis. It pumps up cells so that the fibres in their walls start to slide past each other, making the cells enlarge. The fibres slide in some directions more than others, shaping your embryos as they grow. Mine too.” I noticed for the first time that her pink belly was quite rounded. “The osmotic pressure in my cells is lower than in yours, but their resistance to stretching is also lower. That's because my cells are reinforced by fibres on the inside rather than outside. By sliding past each other to various extents, sometimes actively, the inner fibres of my cells also shape osmosis-driven growth. Osmosis is our friend: without it neither your embryos nor mine would develop... Do you mind?”

She helped herself to several more of my little ones, then settled down to snooze in my shade. She awoke several hours later, yawned, thanked me for my hospitality and waddled off, pausing in the distance to poop under a calm sky.

Read other ‘Developmental Twists’ articles by Tsuku Mogami

Mogami, T. (2021). Developmental Twists: The Scan. Development148, dev200108. doi:10.1242/dev.200108

Mogami, T. (2021). Developmental Twists: Only Human. Development148, dev200204. doi:10.1242/dev.200204

Mogami, T. (2021). Developmental Twists: Back to Back. Development148, dev200268. doi:10.1242/dev.200268

Mogami, T. (2021). Developmental Twists: A Colourful Character. Development148, dev200360. doi:10.1242/dev.200360

Mogami, T. (2022). Developmental Twists: A Fateful Tour. Development149, dev200453. doi:10.1242/dev.200453