BRAIN DEVELOPMENT – EVOLUTION [ GROWTH & ADAPTATION OF THE HUMAN BRAIN ]

FROM THE single celled product of conception, the human animal grows into a complex, uniquely cognitive being. Evolution has built upon older, more primitive animal brain forms to lead humanity to emotion and rational thought. Over eons of time, neural circuitry has developed to promote and continue to promote individual and collective survival. That’s because the human brain is “plastic,” primed from an extremely young age to learn and change.

EVOLUTION

THE DEVELOPMENT of the human brain is written in millions of years of evolution, its story still unfolding.

Neurons began to emerge with the appearance of multicellular animals. The earliest neural connections formed primitive networks of cells in tiny life-forms swimming in primordial oceans. Today, such systems can still be found in simple life-forms such as jellyfish.

SIMPLE BRAINS

Animals with only the barest collection of neurons can function with surprising sophistication. The marine snail Aplysia has only about 2,000 neurons, yet it is capable of movement, reaction to touch, sensation, and all of the things that make a snail live like a snail. It even can learn despite lacking a true brain. Aplysia’s neurons organize themselves into clumps called ganglia at various points on its tiny body, creating a maze of connections. These neural clumps can amplifY or tamp down electrochemical signals as they pass from neuron to neuron; its neural connections can be strengthened or weakened just as in human brains. Scientists have found that when they shock Aplysia’s tail, it reacts by reflexits neural network contracts the affected flesh to pull it away from the source of the shock. However, things get interesting when the shock is preceded by a light touch against the snail’s flesh. After a few repetitions, the lowly Aplysia has enough neural complexity to connect the two sensa- tions: touch, followed by pain. In time, the light touch alone, with no electric shock afterward, is enough to make the snail recoil as if in pain.

An octopus’s brain is dime size, but it can solve simple problems such as moving barriers to get food.

CHARLES DARWIN KNEW he had opened a tinderbox when he published On the Origin of Species in 1859. He laid out a theory of evolution through natural selection: Individuals that have a biological advantage are more likely to outlive their peers and pass their edge to offspring. A gazelle that is a bit faster than another may outrun the lion and breed fast children the next day. Cuidado, Darwin wrote in his notebook, using the Spanish for “careful.” Taken toits logical conclusion, even humans fell under his theory-an idea Darwin down-played at first because he knew it would be unpopular.