Our Neurons Mastered Electrical Signals 450 Million Years Ago — Thanks to a Virus Infection
On the marvelous origin of the neuron’s myelin sheath.
Around 430–450 million years ago, sea creatures began evolving jaws, bony structures that assist biting. It was also during this time that myelin sheaths first appeared in jawed creatures.
What exactly connected the co-evolution of jaws and myelin sheath is unclear, though there are possible theories I’ll explore later.
Importantly, have you heard about the myelin sheath, the magnificent structure unique to the nervous system? Without it, our nervous system wouldn’t be what it is today—compact and efficient.
Look at some complex species without myelin sheaths, like squids and octopuses. Their unmyelinated nerve fibers take up 15,000 times more space than a similarly conducting myelinated nerve in mammals and consume thousands of times more energy.
If we apply this to humans, the human spinal cord would need to be almost a meter wide if the myelin sheath didn’t exist. Can you imagine our lower back’s width (not diameter) being more than 100 cm (Fig 1)?
