The vast repertoire of life forms existing on our planet, including us, are all unique components of nature that are held together through a common thread called ‘Life’. But every life form, be it a single-celled bacterium or a complex living system of a multi-cellular organism, is bestowed with unique identifying features that make it stand out from the rest.
An human beings, we are greatly blessed for we singularly possess a highly complex 1.5 kg organ that sits comfortably inside our skull and fills the space between our ears. Thanks to this amazingly wonderful organ, we could understand the myriad mysteries of galaxies and unravel the structure of atoms, and have unfolded the secrets of the genetic code, each a daunting challenge on its own. This seat of intellect called ‘brain’ had bestowed us with an unparalleled ability to think rationally, a quality that no other life form, however big and mighty on this planet can boast of.
The unique position of human beings in the entire living world owes greatly to this highly sophisticated organ which is the key to human thinking, learning and all higher mental functions besides being involved in several mundane tasks such as sensing the environment, regulating body temperature and controlling body movements among others. The puzzle of how the human brain allows us to perceive behave, think, feel, and control our environment poses a daunting challenge that has baffled scientists over the years.
The important aspects of this puzzle are to firstly understand how over millions of years the primitive nervous system of our early ancestors evolved into an organ that has made us today the most adaptable and intelligent organism on the planet. Secondly, the challenge before us is to unravel the mystery of how a single fertilized egg cell develops the intricate structure of the brain during the course of embryonic development in the womb. Unfolding how the mature human brain continues to modify itself at cellular and molecular levels to acquire new skills and information in an ever changing world is yet another intriguing challenge that we faces today.
The Evolution of Brain
To understand how the human brain differs from the brain of other animals, let us take a look at how this organ evolved over the years in different animals including us. Each and every being inhabiting our planet today has had a history of millions of years of evolution during which that species was subjected to survival battles with its competitors. In fact, the exposure to many hostile environments allowed the more fit species to survive while the unfit beings that were unable to cope up with the adversities were simply wiped out. Basically, there occur genetic alterations called ‘mutations’ to give-rise to new adaptations in a life form to suit a given environment. In this way, life form that emerge victorious in adapting themselves to their environment are more likely to survive and pass on their genes to the next generation.
As different organisms climbed the evolutionary ladder over millions of years, their brains also got evolved. Although the basic building blocks of this organ – the brain cells – are almost identical in all animals, the evolution of brains of insects, fish reptiles, birds and mammals has been dependent on particular tasks controlled by specific regions of the brain that were crucial to the survival of that species. For example, the nervous system of a jellyfish is very simple as it comprises an undifferentiated network of nerve cells or neutrons that primarily serve to coordinate the animal’s swimming motions. Worms have a simple nervous system, which includes a distinct brain that is connected to groups of neurons organized as ‘nerve cords’ running along the length of their body. Interestingly, even with their brain removed, worms are able to perform many types of body functions that include locomotion, mating, burrowing, feeding, and even maze learning!
Brain complexity in insects is seen as a giant fiber system that allows rapid conduction of nerve impulses, connecting parts of the brain to specific muscles in legs or wings. Such neural connections permit, for example, the cockroach to dart away as soon as it senses any movements or objects around it. Insects thus have astounding sensory reception than any other life form that makes them the most abundant multi-cellular organisms on our planet.
The complexity of brain and its functioning increases as one moves up the evolutionary ladder. The brain becomes much larger and more complex as we move to vertebrates such as fish and amphibians. The spinal cord is protected within the vertebrae of the backbone where lies the nerve fibres that orchestrate a busy two-way highway of communication categorized as motor and sensory pathways. Move up further and see the brains of reptiles and birds, and they appear to be still more complex, especially those areas of the brain are more developed that are devoted to specific senses. For example, crocodiles have huge olfactory bulbs, which is the area of the brain that deals with smell. Then comes a wide variety of mammalian species, having varying brain shapes and sizes.
Evolution of Human Intelligence
Noted scientist Michio Kaku talks about the evolution of the Human brain along with its concurrent structures and functions in the below video.