Origins of Us – Brains: Dr Alice Roberts explores how our species, Homo sapiens, developed its large brain and asks why humans are the only ape of its kind left on the planet today. The evolution of the human mind is one of the greatest mysteries. It is the basis of religion, philosophy and science. We are special because of our extraordinary brains, and to understand why we think and act the way we do, we need to look at where and why our brains evolved.
The Rift Valley in Kenya is thought to be the crucible of human evolution, and here Alice examines the fossils in our family tree which reveal our brains have more than quadrupled in size since our ancestors split from chimpanzees. Research investigating sediments and rocks laid down during the period of greatest brain growth suggests a fluctuating environment may have played a part. Drawing on research on social politics in chimpanzees, the cognitive development of children and the tools that have been found littered across the Rift Valley, Alice explores how and why our ancestors brains became so big.
Successive species of increasingly large-brained humans migrated around the world – from Homo erectus to heidelbergensis, the Neanderthals to us. It has always been assumed the reason that Homo sapiens succeeded where others failed is to do with our large brains. Comparing skulls it’s clear Neanderthals had just as big a brain as us, so why is there only us left? Alice goes to meet Svante Paabo, who is decoding the Neanderthal and human genome, and Clive Finlayson, who is unearthing the Neanderthals’ final settlement, to try to find out.
Origins of Us – Brains
A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a vertebrate’s body. In a human, the cerebral cortex contains approximately 14–16 billion neurons, and the estimated number of neurons in the cerebellum is 55–70 billion. Each neuron is connected by synapses to several thousand other neurons. These neurons typically communicate with one another by means of long fibers called axons, which carry trains of signal pulses called action potentials to distant parts of the brain or body targeting specific recipient cells.
Physiologically, brains exert centralized control over a body’s other organs. They act on the rest of the body both by generating patterns of muscle activity and by driving the secretion of chemicals called hormones. This centralized control allows rapid and coordinated responses to changes in the environment. Some basic types of responsiveness such as reflexes can be mediated by the spinal cord or peripheral ganglia, but sophisticated purposeful control of behavior based on complex sensory input requires the information integrating capabilities of a centralized brain.
The operations of individual brain cells are now understood in considerable detail but the way they cooperate in ensembles of millions is yet to be solved. Recent models in modern neuroscience treat the brain as a biological computer, very different in mechanism from an electronic computer, but similar in the sense that it acquires information from the surrounding world, stores it, and processes it in a variety of ways.
