What Makes Us Different? The Peculiarity of the Human Brain

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Biology 202

2006 First Web Paper

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What Makes Us Different? The Peculiarity of the Human Brain

Brittany Peterson

Human beings are exceptionally good at wondering. Many of the most famous pieces of writing in history have been on the subject of human nature. These writings are so popular because they address a subject of interest to all of us: what lies at the root of our humanity? The forces that most commonly motivate human beings reflect this desire: in each religion can be found a particular definition of what it is to be human; in possessions, wealth and career lie a way to define oneself based on goods and accomplishments; and in the bonds we choose to form with other human beings, we seek to find a reflection of ourselves and a way to define ourselves based on how we fit in with others.

A major part of being human lies in the differences between us and other animals. Long before humans could map out the brains of various animals using computers, these essential differences were instinctively sensed. The writers of Genesis, for example, depict Adam as separate from other creatures; created last, in the image of God, and wielding power over other creatures- specifically the power to name them.(4)

These differences are a result of the gradual process of evolution. The most important thing separating humans from other creatures is the structure and sheer power of our brain. Time after time, it has proven to be selectively advantageous to have a large amount of brainpower, and the composition of the brain has been the most potent force in the evolution of human beings.

How did this process begin? The first organisms were single-celled, it is not until around 600 million years ago that we have evidence of multicellular life on Earth.(3) Cells began living in colonies because it was evolutionarily advantageous to do so- possibly because they were less likely to be consumed by predators as a larger group, or perhaps to share energy resources. At some point, these cells began to take on different functions within their colonies.

The most primitive organisms with nervous systems- that is, a system of interconnected nerve cells- are the cnidarians, which have a nerve net consisting of nerve cells scattered throughout the epidermis. Another type of primitive nervous systems include those of echinoderms, such as starfish, which consist of a central nerve ring and five radiating nerves. The most primitive nervous system that includes a brain is that of the annelid. Leeches, for example, have only a brain, two nerve cords, and segmental ganglia running throughout their bodies. Insects have a similar system.(2)

Mammalian brains are fundamentally different from these types of organisms in one particular way: the three main functions of the non-mammalian brain work in three separate sections of the brain, but in mammals they are centralized and are all located in the forebrain.(6)

Humans possess the most complex brains of any mammal, with a number and density of neurons that allows for highly complex thought. This density allows for infinite numbers of thought and for infinite numbers of individual brains. This type of variability is part of what gives humans their unique consciousness. It is difficult to define the sense of "me" that humans have, the sense that we are capable of change, of moral decisions. The complexity that allows for this has evolved over millions of years. It is thought that the first ape-like humans split off from apes at around 5 to 7 million years ago.(5) The reasons that larger brains were continually selected for over the next several million years is unclear. Considering the great amounts of energy needed to support such a brain during fetal development and during life itself, the benefits must have been enormous. These benefits probably included the ability to continually make more complex tools that allowed humans to take more efficient advantage of the resources around them, the ability to understand and control fire, and the ability to think creatively to escape predators and threats involving the elements. Whatever the reason, brain size continued to increase, from the first apelike humans to the slightly more human-like Australopithecines to the early homo sapiens, later humans, and their cousins the Neandartals.(1)

Our consciousness of being is what makes us human. We value it before we even know what it is; small children respond to faces more than to any other stimuli and newborn infants know their mother's voices. The connections we have to others, and the sense of individuals as entities to be learned about and explored in order to learn about and explore ourselves is ingrained. I believe that this tendency to consider individual identity important has itself been selected for over time, since it is with this sense that people strike out on their own to invent and create. Creativity and the ability to think of new ways of doing things- from new, more ingenious stone tools to the wheel to the Internet to quantum physics- has allowed the human race to continually improve its lifestyle and to remain the preeminent species in the world. Our consciousness of being human is what allows us to continue being human.

1) 1) Palomar College Anthropology , Very informative regarding human evolution over time- e.g. Australopithecines, early homo- good reference for basic facts on this subject.

2) 2) Gilbert, Scott F. Developmental Biology, seventh ed. Sinauer Associates, Inc.: Sunderland, 2003.
I used this textbook to find information on the form of the nervous system in various types of organisms.

3) 3) The Evolution of Life On Earth- Scientific American, Even though I only used this site to reference the time of the evolution of the first multicellular organisms, I enjoyed reading Gould's piece, and have in fact enjoyed all of his writings that I have read; he had a gift for making science interesting and thus accessible.

4) 4) Holy Bible: New Revised Standard Edition. Cokesbury: Nashville, Burlingame, 1990.
This is where the reference to Adam's ability to name the other animals in Genesis comes from.

5) 5) IT "Scientists narrow time limit for human, chimp split." , An interesting article discussing the debate on when humans diverged from apes; I used it to find the currently agreed-upon date.

6) 6) The origin and detailed structure of the human brain , This site provided an interesting bit of information that I had not previously realized, about the way in which various structures, each performing a different function in the premammalian brain, are more condensed in the mammalian brain; a structural distinction I found intriguing and meaningful.

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