When thinking about evolution, you could ask yourself what appeared first "The chicken, or the egg?" Some individuals would simply laugh and say, "The chicken, because without it how could there be an egg?" Others would say, "The egg, because without the egg how could there be a chicken?" Speculation combined with scientific research could provide us with that answer. Just like the question about the chicken and the egg another disputed topic is still being talked about within human evolution. Did our common ancestors’ brain develop before or after we started to become bipedal? To best answer that question lets first understand each acquired trait.
What is bipedal? In the book Human Origins, Evolution and Diversity,[Jur13] the definition of bipedal is "Walking on two feet. Walking on two legs is the single most distinctive feature of the hominoids." Being bipedal is not easy; balance with the help of evolution has made it possible for modern day Homo sapiens to be bipedal. So what took place to change the body structure from arboreal tree dwelling hominoids to bipedal? Darwinism is explained by Dr. Aaron G. Filler, in the book The Upright Ape, A new Origin of the Species, it talks about species evolving over time. Anthropologists suggest that evolution to bipedal freed the hands for carrying objects, and for making and using tools. Another suggestion indicates that it helped with spotting potential danger, large cats, leopards, lions, saber-tooth's etc. Bipedal locomotion helped with walking long distances, and tracking animals across the open plains. Anthropologists don't know exactly what triggered the process into acquiring this specific trait, but they are certain that the factors listed above helped with acquiring this trait.
The bipedal structure takes place in the pelvis. In hominoids, the pelvis is much shorter, more girth, and broader which extends around to the side. Because of this, it helps with stabilization of the weight from the lower back to the hip joints. The foot also plays an important role, instead of grasping tree branches and limbs, the foot is used like a prop, landing on the heel and propelling/pushing from the toes. Because of this acquired trait hominoids, which adapted to bipedal locomotion, are less efficient in trees and climbing, but more efficient with traveling greater distances.
Have you ever heard someone say, "If you make two fists with your hands and put them together, that will be roughly the size of your brain."? Sometimes I wonder if some homo sapiens actually have a brain at all. How did our Ancestors brains actually evolve and why? Growing up I learned that if you touch a hot surface you will be burned. I learned that, and because I learned that I can tell other people that if you touch anything hot you will most likely be burned. What I learned is what we call a "learned behavior". Anthropologists have theories about how the brain evolved into modern day Homo sapiens, but it is believed that with new diets, means of travel, and learning etc., our early ancestors started developing more complex brains. Because of the increasing brain sizes, over millions of years, it helped with new ways for hominoids to adapt to different climates, elevation etc. Tools started to become more efficient, and social behaviors better learned. Because of the increasing brain size, anthropologists believe that it helped shape the skulls which we see today. With the brain size increasing, the cranium also grew, the occipital bun became less pointy, and developed larger foreheads.
Which came first, bipedal locomotion or brain development? One of the ways which you can answer this question is by measuring the opisthocranion opisthion distance and the oral distance of the fossils. By doing this, you can know if the species are bipedal, or if they walked on all fours. Another way is by measuring the cranium. By measuring the area of the cranium, and estimated cranial capacity you can know how big the brain was during its life span. By understanding the age of the bones you can tell what time frame the species lived, if it was bipedal, and the size of the brain. University of Texas at Austin has something to say about this question, "…in 1974, Donald Johanson found the nearly complete fossilized skeleton of Lucy, a member of the species A. afarensis dating to 3.2 Ma. Lucy was unique at that time, because she exhibited both a small brain, similar to that of modern chimpanzees, and the highly derived features characteristic of bipedalism, similar to humans. As other contemporaneous and older fossils (perhaps as old at 7 million years) are found, scientists have revised the bipedalism timeline. Today, the evidence undoubtedly demonstrates that bipedalism was the first hallmark of the hominoid’s lineage. One of the advantages of bipedalism is the freeing up of the hands to produce more technologically advanced stone tools, which may have led to a better diet that affected brain size." Because of information like this, scientists and anthropologists throughout the world are solving how we evolved and maybe what modern humans might look like in the future.
The chicken and the egg question has lead the research of many topics within the evolutionary process of Homo sapiens. Because of technology, and greater scientific research we are finally understanding how our ancestors came to be. Before this research paper I thought that our ancestors had to develop greater brain function to get where they got. They did develop greater brain function, but it came a lot slower than I anticipated. Who knows what evolutionary features humanity will acquire in the future.