Discovering the Things that Make Us Human: Evolution of the Brain

Discovering the Things that Make Us Human: Evolution of the Brain

There is a powerful sentiment among many people that human beings are the most intelligent and complex animals on earth. Our ability to use language is matched by no other species. It makes sense to assume that whichever characteristics of the human brain arent possessed by other animals, specifically primates, our closest evolutionary relatives, are the ones responsible for the acquisition, production, and comprehension of language. As the relatively new field of neuroscience develops, scientists are beginning to study the evolutionary relationships of brain organization and function in an effort to understand the regions of the brain responsible for language, abstract thought, and self-expression. This discipline, known as Paleoneurology, examines the development of the hominid brain (1). Paleoneurology has its roots in the fields of neurology, paleoanthropology, and primatology. There are two methods used by Paleoneurologists to study brain evolution: the examination of fossil skulls and endocasts, and comparative primate neuroanatomy (2). The study of the evolution of the brain is useful, because it allows for an understanding of the origins of the structural differences between humans and other animals--in effect, what makes us human.

According to the fossil record, the first brain structure appeared in reptiles around 500 million years ago. The functions of this hindbrain included breathing, heart beat regulation, balance, basic motor movements, and foraging skills (1). An interesting trend in brain evolution is that more evolved species tend to preserve the structures responsible for basic behaviors. In other words, evolution is the process of acquiring more and more sophisticated structures, not simply the addition of different structures. Therefore, the modern human brain contains the primitive hindbrain region, often called the protereptilin brain (1), and it is the seat of fundamental homeostatic functions. The major structures found in this region of the brain are the Pons and Medulla. About 250 million years after the appearance of the hindbrain, a new region known as the paleomammalian brain arose. This region consists of the hippocampus and cerebellum and is often referred to as the limbic system. As might be expected, this region is associated with more complex functions such as emotional, sexual, and fighting behaviors (1). The newest and most intricate area of the brain, the cerebrum, was first developed around 200 million years ago. The highly convoluted surface of the cerebrum is called the neocortex.