During the past 2 centuries, curious scientists have laid the foundation for answering the question of human origins using advances in technology. Fossil evidence and genetic studies have made this quest possible. Patient accumulation of evidence has led to gradual acceptance by the general public of the conclusion that our species has evolved, during 5 million years, from an ancestor in common with the four great apes in the remote past.
Aristotle, considered the founder of biology, was the first to effectively place animals in a specific order of taxonomy. By organizing species into common groups, he established a foundation for understanding the similarities among life forms on this planet. Even so, he taught the eternal fixity of all species.
Linnaeus, the father of modern taxonomy, took the science of classification to the next level. A species is seen as a group of individuals that share enough biological similarities that they can interbreed with one another successfully. The primate order, which was formed about 70 million years ago, is divided into two suborders: Prosimii and Anthropoidea. Being hominoids, humans and pongids (apes) are placed into the same taxonomic family due to their biological similarities.
Linnaeus’s writings were available in the century before Darwin’s On the Origin of Species (1859). If it were not for Linnaeus’s work in biological classification, it would not been possible to speculate on how some species die off and new species are formed. This was later explained by Darwin with his theory of evolution. Darwin realized that species are not in a static state, since everything is in a dynamic process that results in constant change. With the uses of relative dating techniques, Darwin came to the conclusion that fossils in rock strata demonstrate a continuous organic evolution that led to a species’ survival or extinction.
Advances in radiometric techniques have allowed scientists to date fossil evidence more accurately. The modern technology of chronometric dating, through the use of radioactive decay, has greatly strengthened the hypothesis that our species has evolved from a common ancestor close to the four living great apes (orangutans, gorillas, chimpanzees, and bonobos). Darwin argued that our evolution took place in Africa. Scientists realized that, to find the truth about our evolutionary past, they had to gather empirical evidence to solve the mysteries of our origin and history. For more than a century, they have searched for the so-called missing link between the great apes and humans.
The first major discovery that established our descent from a common ancestor with the apes was made in Africa, and known as the “Zinj” skull. This unearthing in 1959 by Mary D. Leakey shed light on the hypothesis that our species is more similar to the great apes than had been thought. Several decades ago, anthropologists thought that the split between fossil hominids and fossil apes had occurred during the Miocene epoch, about 12 million years ago. However, more recent hominid species found in southeast Africa are also pongid-like. This evidence from the Pliocene, about 5 to 7 million years ago, determines that our split from the pongids was more recent than had been thought.
During the Miocene, hominoids emerged in many varieties. Before the end of the following Pliocene epoch around 3 million years ago (mya), the environment had changed; the tropical jungles of Africa had become scattered woodlands and open savannas. This change directly resulted in the split between early hominid-like hominoids and pongid-like hominoids. Based on fossil evidence, this split from Pliocene pongid-like homi- noids happened roughly 6 mya. The species that were able to adapt to living a terrestrial life survived to form our more recent ancestors. BipeDalíity is the true separation between the fossil apes and more human-like forms. Many other specializations like tool-making, articulate speech, and a far more complex brain where all later developments during the past 3 million years.
An early ancestor that was successful in this transition from quadrapeDalí movement to bipeDalíity is known as Australopithecus afarensis; the features of afarensis are from the neck up chimpanzee-like and from the waist down human-like. The discovery of afarensis was only the beginning; scientists are still trying to uncover more clues from our distant past. Interpreting the evidence in order to determine the evolutionary advantage for becoming bipeDalí continues.
Owen C. Lovejoy, an anthropologist and an expert in anatomy, was the person whom Donald C. Johanson trusted in studying his discoveries at Hadar. Lovejoy has been an influential contributor to the understanding of our past; he believes that our evolution was based on a social advantage that leads to our survival. Hominids created an evolved breeding strategy that enabled humans to raise fewer children, but also allowed them to focus on the success of a limited number of offspring. Lovejoy believes that hominids’ opportunity for success revolved around living in large monogamous groups. This is supported by the secondary characteristics that have formed to create the modern human; these phenotypes control the amount of competition between males. In the animal kingdom, an obvious way for species to determine if a female is in heat is to observe the inflammation of sex organs and the growth of breasts. These characteristics are clear signs that lead males to fighting, which would lead to the disbanding of groups. In hominids, it is difficult to make this distinction when a woman is not pregnant. Many criticize this theory of a monogamous relationship, because it goes against Darwin’s evolutionary logic. Without the most dominant males passing on their genes to multiple partners, how would hominids survive? Lovejoy answers this argument with the theory that by males appealing to a singular mate, using their time during the day to gather food for not just themselves but also their partner, they allow the females to spend all their time raising the offspring. This allows for a successful passing on of their genes. Another major distinction between the pongids and hominids is that we evolved from being simply insectivores or vegetarians to being primarily omnivores; this allowed for a broad diet that provided a better opportunity for survival in an environment where grasslands where slowly replacing forests in Africa. Through cooperation, afarensis, Homo habilis, and Homo erectus allowed humans the opportunity to exist. The creation of a more complex brain came later in the development of Homo sapiens sapiens.
From close genetic similarities and observations of human and pongid social behavior, many scientists now recognize that, as mentioned earlier, the split between the hominids and pongids did not occur in the Miocene epoch, but more recently in the Pliocene. In recent decades, biologists have come to the conclusion that our species is more similar to the great apes than had been imagined even by Darwin.
Ryan J. Trubits
See also Aristotle; Darwin, Charles; Evolution, Organic; Fossil Record; Fossils, Interpretations of; Fossils and Artifacts; Haeckel, Ernst; Huxley, Thomas Henry;
Olduvai Gorge; Scopes “Monkey Trial” of 1925
Birx, H. J. (1988). Human evolution. Springfield, IL: Charles C Thomas.
Foley, R. A., & Lewin, R. (2004).Principles of human evolution. New York: Wiley.
Johanson, D. C. (1994). Ancestors: In Search of human origins. New York: Villard.