Amanda Haas

15 February, 1999

Freshman Seminar

Tietjen

Brain Evolution

The brain is a very important part of the body that controls activity and behavior. Over time, the brain has evolved to allow creatures to become more intelligent and efficient. A bigger, better brain is important. As the brain has evolved, we can see more sophisticated communication and the beginning of language. Those with bigger brains have an advantage in such activities as hunting, preparing food, speaking, and inventing. As we view the evolution of the brain, we will investigate "Mister Ples," the relationship between chimpanzees and humans, and the importance of throwing.

Mister Ples, a creature from the clan Australopithecus africanus, has been studied using fossil partial skulls and computer technology. His brain case is found to hold near five hundred fifteen cubic centimeters, a size that is comparable to the brain of the largest male chimpanzee. Scientists originally thought the brain size was six hundred cubic centimeters, but a new computer-generated test has shown otherwise. Our brain size has doubled over the past two million years to reach 1200 cubic centimeters. Below is a diagram comparing millions of years to cranial capacity. It displays both Homo Sapiens and Australopithecines.

The Australopithecus africanus were bipedal and had the intelligence to build chopping tools. It is believed that they are the missing link between apes and humans, and we can see this through their brain characteristics. The skull of Mister Ples is around 2.6 or 2.8 million years old.

Another way that we can study the brain's evolution is by comparing the human brain to that of the chimpanzee. It is known that chimpanzees look and act in ways similar to us, and they can understand our language up to a certain point. Now scientists believe that humans and chimpanzees actually have some similar brain structures that control communication. Chimpanzees are our closest relatives. They have similar brains, but the areas of the brain that are similar are those that control language. These are located in the planum temporale, an area that is larger on the left side of the brain.

The new information supports ideas that chimpanzees use language in some way. The planum temporale is linked to schizophrenia, dyslexia, and a talent for music, all traits that only humans are believed to possess. This causes even more questions for researchers. Some chimpanzees have learned up to one hundred words in sign language so they can communicate with humans. They are also familiar with a language that is created using computer icons. Researchers already know that humans and chimpanzees are genetically ninety eight percent similar. Chimpanzees have the ability to understand commands as a 2.5-year-old human can understand sentences. Chimpanzees have a communication system in the wild, which consists of grunts, hoots, and physical gestures. They seem to have a form of language of their own that we have yet to understand. To proceed with the study, researchers are going to analyze the chimpanzee brains at work using positron emission tomography. The similarity between human and chimpanzee brains is also present in the orangutan and gorilla. The research on the planum temporale could lead to more answers on the evolution of the brain.

Now an interesting idea is introduced. William H. Calvin supports an idea that the brain has evolved due to the ability to throw. He says that the simple act of throwing a rock at a non-moving object uses the brain because you must be precise in the timing when you release the rock. We can observe that young children find excitement in throwing, hammering, and the idea that their right hand may be stronger than their left. Throwing rocks and spears requires more neurons in the brain because of the need for timing accuracy. In archaeological records, the largest form of hunting is by throwing spears at large animals. Even though most scientists focus on hunting big game when speaking of hominid hunting, some believe that it is more likely that humans began by hunting small animals. Some societies today that do not have agriculture like we do in America are partial to eating small game, so this supports the idea that our ancestors may have hunted small game as well. There is only one reported occurrence when chimpanzees throw rocks as a form of hunting, and they simply throw rocks as a scare tactic. It is suggested that the idea of hunting with rocks began by throwing rocks to threaten the prey and progressed to aimed throws. This progression requires more thinking... and a bigger brain. Throwing could have allowed hominids to expand their population because of the fact that small animals have more widespread habitats.

It takes more brainpower to throw at a moving object. The hunter must decide the trajectories of both the rock and the prey. The "faster-is-better" idea suggests that a faster pitch goes farther and has more stopping power. Bigger brains enable us to throw faster, so the new idea is "bigger-is-faster-is-better." A creature with a bigger brain might throw a baseball-sized rock quickly with one hand instead of using an over-the-head motion with a melon-sized rock. Hominids probably threw in an over arm way like a child instead of the complicated way that a baseball player would throw because their brains were not as complex. There are many ways that precision-throwing can require more neuron activity in the brain than the simple act of picking up a rock and tossing it. Because throwing has been around for millions of years, it makes sense to say that throwing could have made a large contribution to the evolution of the brain. It probably led to the carrying bag, a popular hominid invention, because they needed a way to carry their rocks and spears.

According to Calvin, the hominid brain has tripled in volume through the past several million years. Bipedalism, culture, problem-solving, tool-making, invention of carrying bags and fire-starting, and the family with two parents are all important things that require thinking; but they are not likely to have caused growth in the brain because they do not have the bigger-is-faster-is-better characteristic.

Bigger better brains needed for precision throwing brought about language and intelligence. After the Ice Age, the ability to hammer and throw helped our ancestors to survive, and their children began to throw and hammer by instinct. The evolution of the brain has allowed other new actions besides communication. Timing precision has allowed us to develop musical skills and play sports, among other things.

William Calvin believes that the ability to move rapidly, such as the motion of the arm when throwing could have brought about certain aspects of intelligence as foresight, language, and musical skills as he discusses in "The Emergence of Intelligence." Most people believe that cleverness is the essence of intelligence, with other important aspects such as foresight, creativity, and the ability to predict. No one will agree on a set definition of "intelligence" because it can have many meanings. Our intelligence could have risen just because other animals do not have as much brain as we have. For example, the cerebral cortex is involved in decision making. Ours could cover four pieces of paper if flattened and spread out, where a chimpanzee's would only cover one sheet. However, Calvin believes that the numbers do not matter as much as does the fact that our brains are more specialized.

A notably intelligent person is able to think of many ideas at once and answer questions quickly. Another aspect of intelligence is versatility. For example, an animal with minimum intelligence may eat a certain leaf all the time where humans usually vary what they consume and consider their options. Young animals discover new things all the time when playing. It is possible that the animals that have longer juvenile periods are at an advantage as are those who have a longer life span. Another way to intelligence is having a social life. Those who associate with other groups, or even others in their same group, have the ability to imitate others' discoveries and inventions.

Versatility becomes very important when something occurs such as a change in weather. The ice age began two and a half million years ago. The cooling temperatures devastated rain forests, vegetation, and even animal populations. Lightning strikes caused huge forest fires that wiped out even the grass. However, when grass began to grow again, the animals that survived began to multiply quickly. If the climate had changed more slowly, the hominids would have been able to adapt while living as their parents had taught them. However, they were forced to improvise. They learned to eat grass, hunt for big animals that herd together, and share. If a hunter killed a large animal that was too much to eat, he would give meat to others in the hopes that they would do the same for him if they were in the same situation. Because they shared food, they fought less and had more time to do productive things such as searching for more food. This indicates that the ice age and other climate changes could have been factors in the evolution of the brain and intelligence.

The ice age helped to bring about language. Human language shows the passion for finding patterns and putting things together. For example, we combine words to make sentences, arrange steps to make dances, and put notes together to make a song. Language is a key factor to indicate intelligence. A group that is able to communicate in such an advanced way can teach others and learn from them, and they can work together, so intelligence falls in place. After reviewing the work of researchers, one can see that no one has definite answers about the evolution of the brain, but all of the possibilities discussed seem plausible. Maybe we will find answers in the future.

 

REFERENCES

Bowman, Lee. Controversy expands over evolution and brain size. [Online] Available http://www.nando.net/newsroom/ntn/health7_19043_noframes.html,January 29, 1999.

Calvin, William. A Stone's Throw and its Launch Window. [Online] Available http://williamcalvin.com/1980s/1983JTheoretBiol.htm, February 5, 1999.

Calvin, William. The Emergence of Intelligence. [Online] Available http://weber.u.washington.edu/~wcalvin/1990s/1998SciAmer.htm, February 5, 1999.

Chimps Like Us/ We're Like Chimps. [Online] Available http://www.geocites.com/RainForest/Vines/4451/ChimpsLikeUs.html, February 5, 1999.

Falk, Dean. Hominid Brain Evolution: Looks Can Be Deceiving. [Online] Available http://cas.bellarmine.edu/tietjen/images/hominid_brain_evolution2.htm, January 29, 1999.

Evolution of the Brain

Origin

Before discussing the actual evolution of the brain, one should look at the origin of the brain. Thurston Lacalli, of Canada, and Linda Z. Holland, of California, both collected information that shows how we can trace the origin of the brain back to simple nerve bundles from salps and starfish, which are both sea creatures. Salps have been determined to be a distant relative of humans; they belong to a group called the chordates. This information can help us see how we can relate salps to the brain. During their life, chordates have a hollow nerve tube, which is equivalent to our spinal cord, that is held in place by stiff tissue. This tube slowly becomes the backbone. Although chordates do have a supported backbone, they do not have a noticeable ‘head’ with a brain like humans do. However, chordates possess structures that compare favorably with the structures of human brains. Lacalli studied the salps’ nerve cells and concluded that they are similar to those in the human brain. Also, the end of the chordates’ nerve cord swells to form a brain much like our spinal cord swells at one end. Both the salps’ brains and our brains are involved in a vision process and in motor development (Gee 1). Finally, Lacalli and Holland have determined that many neural structures in both the salps and starfish greatly resemble some structures in our human brain (Gee 2).

 

Throwing

Now that the origin of the brain has been discussed, the actual evolution of the brain can be explained. A man by the name of William Calvin believes that the act of throwing plays a great role in brain evolution. The throwing of spears or rocks requires special timing; the person must be accurate in his or her timing when throwing. Calvin says that improving timing accuracy calls for seeking out timing neurons from another place in the brain- a process called brain reorganization. The process is a key factor in brain evolution because it demands that different areas of the brain be explored and used (Calvin 2).

From gathering additional information, Calvin also discovered that early hominids preferred to hunt small game such as rats, lizards, toads, mice, bats, and morsels. He supposed this required a good amount of thinking, as the hominids realized that smaller game reproduced faster, were easier to hunt because they did not have to be pursued over far distances, and stored foods- like seeds- that the hominids could also eat. The small game was also much more defenseless than the larger game. Therefore, this paragraph sums up how when hunting game, aimed throwing could lead to success, which in turn, leads to reward- in this case, food (Calvin 2).

When hunting, an early hominid was very likely to have to throw at a moving target. This required the hominid to use a more sophisticated process. Mentally, the thrower has to figure out the rock’s trajectory as well as the prey’s trajectory. Another important thing that the thrower had to learn was to block the first part of the arm motion with his or her body. This strategy would definitely surprise the intended prey, and the thrower would hit his or her target. Along with this idea, the throwers also learned that the faster the throw, the better the results. The faster the throw, the farther the hominid could throw and the greater the stopping power. Calvin believes that brains got larger to allow for faster throws, so the hominids with bigger brains survived because they could hunt down their prey for food. This learning process uses applied thinking skills, which further allowed for brain development (Calvin 3).

Upon researching, Calvin compared the throwing style of spear throwers to the throwing styles of modern day humans. He concluded that the overarm throwing style that children use is more similar to the hominid throwing styles than the styles of baseball pitchers. In the hominid and child throwing style, the elbow uncocks, and this is the biggest factor in launch velocity. Another aspect of this style is that the shoulder motions and the axial motions are slower. However, both styles of throwing demand timing accuracy, which shows how the timing in our past has led to new things of today- athletics, music, and sequencing in grammar (Calvin 3 and 4).

Along with throwing, hammering is believed to be related to language development, which is a degree of brain evolution. Calvin believes that the motion of hammering is interrelated with language, memory, and other motor developments. Two scientists, Ojemann and Mateer, found that language began with oral-facial motor sequencing, or imitating various facial expressions. This action takes place in a dominant hemisphere of the brain- the hemisphere that also supports such skills as hammering. Mateer considers manual tasks and facial tasks to be related. He, along with other scientists, states that the timing issue can come into play at this point; the repeated success of throwing lets motor timing skills contribute to the timing of language outbursts (Calvin 7).

 

Another Theory

Carl Sachs, a paleoanthropologist, proposes his theory on the evolution of the brain. Sachs states that the human brain has expanded as a whole throughout many years. For an explanation of exactly how the brain expanded as a whole, Sachs calls for a "decoupling theory"; in other words, he thinks that as the human body grew larger, the brain did, too. As the brain grew, more mental processes and behaviors developed along with it. These processes simply correlated with the environment that the human was in. Sachs says that this theory shows that Australopithecus evolved to early Homo and Homo erectus to Homo sapiens (Sachs 1).

 

Climate and Brain Evolution

It is uncertain when intelligence actually developed; intelligence includes language skills, planning, logical inferences, rules, and music. Possibly, intelligence emerged as hammering and throwing skills became better. These actions could have built the foundations of syntax, sentence structure, and logical thoughts, including planning. The hominids wanted to earn their own way, and developing intelligence could help them (Calvin 1). When a climate change is considered, brain evolution and the development of intelligence is supported. If a temperature drops a great deal or changes over so many years, then the plant and animal species change, too. The hominids present during a climate change would have to learn how to adapt to the change; this could mean eating differently or hunting differently. Our ancestors would have to find a new way of living in a new environment. Those hominids that began to develop a sense of intelligence were able to survive during a change in climate or environment (Calvin 2). As one can see, flexibility of a hominid’s behavior was absolutely necessary for his or her survival (Miller 1).

 

The above chart shows the different skulls of the various hominids and what tools were common to use during their time. The significance of the chart, which was from an article by Mary Leaky, is to show the change in skull size through each of the hominids. One can easily see the size brain that could fit inside the skull, and one can see the how the levels of intelligence increased based on the different tools used.

References