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A baby sea turtle has just hatched. It has never seen the sea. So why does it head straight for the water? Nobody taught it. Things you can do from birth, without learning, are called instincts. So where in the body does an instinct live? The answer: in wiring that was connected before birth.
Your body is full of nerve cells. Each one reaches out a long, thin wire, linking to the next. When your eyes, nose or skin pick something up, it turns into a little pulse of electricity that runs along those wires. Wherever the wires lead, the pulse goes. When it reaches a muscle, the body moves.
Learning means slowly rewiring after you're born. Instinct is different. That wiring is already in place before birth. Who does the wiring? Genes. Genes don't hold a video of crawling to the sea. They're more like a building plan. The plan tells growing nerve cells which way to reach, and whom to connect with.
Along the way are chemical signposts. Some pull the wire closer, some push it away. Following them, the wire finds the right place to connect. Animals of the same kind share nearly the same plan, so they end up with nearly the same wiring. That's why every baby turtle crawls to the sea. Here's an experiment. Lab mice have never seen a hawk, not in generations.
Scientists showed them a dark shadow growing bigger overhead. About three out of four mice started running for cover in under a quarter of a second. There's no time to think. The moment the shadow hits the eyes, ready-made wiring connects straight to run. Hunger is wiring too. Deep in a mouse's brain, sits a small group of nerve cells in charge of hunger.
Scientists switched on about eight hundred of them with light, and mice that had just eaten started feasting again within minutes. People have them too. Touch a newborn's palm, and the tiny hand grips tight. That wiring was built in the womb. Later, newer parts of the growing brain take control of it. By about six months, the grip is gone.
Instincts can also be fooled. A baby turtle's wiring heads for the low, bright side. Turn on a streetlight by the beach, and it crawls inland. Because the wiring doesn't know what the sea is. It only knows one thing: see this, do that. So a loud bang makes you flinch. Hunger sends you looking for food. You never had to learn that. It's wiring connected for you before you were born.
What else does your body do all by itself that you'd like explained? Tell me in the comments.
An instinct is
nerve wiring that was
connected before birth.
When your eyes, nose or skin pick up the right signal, a pulse of electricity runs along that wiring to your muscles. The body just moves. No thinking, no learning.
Humans have fewer instincts than many animals. As we grow, newer parts of the brain take charge of some of them and replace them with learned skills.
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