Introduction to Evolution
There are many theories that explain the origins of humans. These theories range from the fantastical to the rigorously peer reviewed. This debate, to the amazement of empirically based minds, still persist even today. Some of the factors that determine the theory one accepts to be true include: the level of education, religiosity, age and also vulnerability to conspiratorial and/or emotional thinking (Gallup). The two major theories that attempt to explain the evolution of humans are creationism and Darwinian evolution theory. Other theories which can be categorized under the creationist label include theories that make claims of the origins of the origins of the universe from aliens, rising forth from the earth, and descending from “the heavens.” Theories that try and explain the origins of humanity by making fantastical claims about a connection to extra-terrestrial beings from outer space are almost always connected to the pseudo-archaeological, pseudo-historic, and pseudo-scientific theory of Ancient Aliens (Coppens).
Many people, including the religious dismiss the claims made by the Ancient Aliens theory, due to different reasons. Apart from those that require empirical evidence for any claims, the denial of this theory by especially the religious, raises a curious case. Most religious people advocate for the theory of creationism. This theory in its newest and most “reasonable” iteration, posits the intelligent design argument (Numbers 136-9). The proponents of this theory continue to argue that divine powers responsible for the creation the universe created humans. Creationist claim that God having created everything else, created humans. One of the major creationist theories is the Christian theory, mainly due to the majority of religious believers belonging to Christian faith. The Christian theory of creation claims that humans were created on the sixth day of creation, in the present form we see humans today (Numbers 141-2). The proponents of the creationist theory strongly disagree with the theory of evolution, citing the divinity of the humans as the pinnacle of creation. According to creationists, humans hold a special place with regard to other lifeforms, having been created in the likeness of the Creator. They therefore vehemently disagree that humans evolved from “monkeys.”
Most empirically based minds, follow the coherent trail of evidence when confronted with an issue. With regard to the origin of humans, the most rigorously, evidence-based theory that explains the origins of humans is the evolutionary theory. The theory of evolution, is a biological theory that postulates that the various flora and fauna we see around us have their origins from earlier types of flora and fauna (Thagard and Findlay n.p.). The iterative modifications over the generations have resulted to the complex features and discernible differences that can be observed today. The theory of evolution is one of the fundamental realities of the modern day biology. The diversity of life is mind-boggling. With over 2 million species being named and described, estimates approximate that over 30 million species remain undiscovered. The remarkable thing about this is that the extraordinary heterogeneity in dimensions, appearance, configuration, and behaviour all stemmed from ignoble bacterial life forms as evidenced in the theory of evolution. Humans are no different from other life forms in this regard. In line with, this paper will discuss the major events in the chronology of human evolution.
Introducing Human Evolution
Human evolution refers to the process through which humans progressively developed from our now-extinct primates. Scientifically, humans are Homo sapiens, a species that resides on the ground, walks upright and bear culture. Research shows that the modern days humans evolved in Africa approximately half a million years ago. Human evolution is supported by abundant fossil, geological and archaeological evidence that show that modern day humans evolved from the preceding ancestor species millions of years ago. These ancestors to modern humans include Ardipithecus, Australopithecus, and a varied species of the Homo genus. Contrary to what many people seem to think, that humans are descended from Neanderthals, they are in fact not our ancestors (Bar-Yosef 7;15). The truth of the matter is that earlier Homo sapiens evolved along Neanderthals – who we share a common ancestor with. Recent evidence shows that there might have been cross-breeding between these two species (Dalton).
Besides Neanderthals, our ancestors to earlier humans did always share the environment with other ape-like primates for instance the modern day gorilla to the Dryopithecus, which have long gone extinct. Ever since the writing of the essential books On the Origins of Species (1859) and The Descent of Man (1871) by pioneer of evolutionary theory Charles Darwin, there has been a many research to determine the exact nature of evolutionary heritage. Of note, as earlier touched on, Darwinian evolutionary theory’s claim is not that “man came from apes.” Man had a common ancestor with these species, therefore the aforementioned statement is quite the exaggeration of the truth. By the same token, another popular notion that is all too common that we might have heard – that particular now extinct species constitute the ‘missing link’ between humans and apes – should similarly be dismissed (Gee n.p.). A more accurate representation is that the ancestral primate is a node of divergence from which varying lineages sprung forth.
Human Evolution
The chief source that we rely upon to detail the progression of human evolution is the discovery of human specimens. It is from the analysis of these fossil records that scientists came to the conclusion that a variety of species existed alongside each other throughout the human species’ history. By analysing fossils, the particular species of an organism for instance humans can be accurately predicted. The location and duration for their lifetimes can also be reliably predicted. What cannot be known for sure, however, is how the specifics of their extinction. To this end, we rely on scientifically informed precis.
As noted, the human evolution story is not clear cut but progressive. Due to this, it is worth noting that the human evolutionary lineage or “tree” is more of a “bush” since it is nearly impossible to connect a flawless progression of the ancestry of humans. In demystifying the lineage of the ancestry of humans, scientific researchers employ highly refined excavation, and dating techniques. These methods are used to draw conclusions from volumes of varying fossils. Research into the evolution of humans further relies on an amalgamation of knowledge from other fields such as genetics, ecology, paleoecology, and ethology (Sinha 17-23). The study of the lineage of humans can therefore be accurately described as palaeoanthropology.
Using the above mentioned techniques, research indicates that humanity has its origins millions of years ago. To be specific, research points to the period between 25 and 5 million years ago, a period referred to as the Miocene Epoch, as the beginnings of the humans. Human evolution has been traced from the eons of the Miocene Epoch to the more recent (with respect to the age of the Earth) Pleistocene Epoch, that is the period between 2.5 million years ago, and 12,000 years ago (Mayor and Campbell 1-2). Research has suggested that the ancestors of the earliest hominins, are Eurasian and African primates that lived in during the Pliocene Epoch (the period between 5.5 and 2.5 million years). While there is not a consensus due to the difficulty in establishing the facts that are extremely archaic, several primates have been suggested by experts to fit this criteria. These include Kenyapithecus, Griphopithecus, Dryopithecus, Graecopithecus (Ouranopithecus), Samburupithecus, Sahelanthropus, and Orrorin (Andrews 122-148). Kenyapithecus inhabited the region which is now Kenya while Griphopithecus inhabited central Europe and Turkey during the period between 16 and 14 million years ago. The best known ancestor primate from Europe is the Dryopithecus which lived during the period between 13 and 8 million years ago. Graecopithecus and Samburupithecus lived at approximately the same period in northern and southern Greece and northern Kenya respectively, about 9 million years ago. Sahelanthropus inhabited the region of modern day Chad between 7 and 6 million years ago a period which the Orronin inhabited central Kenya. Among these earliest ancestors to the early hominins, the ones that have been shown to be the most likely ancestors of great apes and consequently humans, are either Kenyapithecus or Griphopithecus.
The Miocene Epoch that these above mentioned ancestral species to hominins lived was characterized by prominent changes in the climate that affected these species. The changes in climate led to the increase in seasonal conditions due to an unprecedented increase in colder winters, especially to the north of the Equator. Due to these changes in the climate, by the Late Miocene, most of the evergreen thick-vegetated forest habitats that were inhabited by these ape-like primates were replaced by open woodlands, shrublands, and grasslands (van der Made 431-447). This change in environment necessitated locomotion in many types of animals, including primates. Hominins were forced to scavenge in this new environment and even kill to get their food. This new environment favoured larger felines such as hyenas, and dogs. While they provided meat for the scavenging hominins, they would compete with the hominins sometimes even prey upon them.
The change in environment in the late Miocene Epoch demanded behavioural and morphological changes that corresponded to the shift from arboreal to terrestrial life. Among these changes were dietary, social, and locomotion changes (van der Made 431-447). It is worth noting that the ancestors to humans were not exclusively or even majorly carnivorous. Their diet that consisted of tough, coarse vegetation, comprising of seeds, stems, nuts, fruits, leaves, and tubers, can be concluded from analysing dental structures of primate remains showing large premolars and molars coated by a thick enamel. Shifting our attention to movement, the development of bipedalism in early hominids is a major point of note. The development of this mode of movement was necessary to ensure that the hominids adapted appropriately to the woodlands (Gruss, Tobias and Schmitt 2-9). Bipedalism, in particular, obligate terrestrial bipedalism which is the ability and reliance on movement on only the hind limbs) is, as a matter of fact, the differentiating trait is used to classify Hominins.
It is worth noting that bipedalism in general is not unique to humans, however, our specific form of bipedalism is unique to us. The mode of bipedalism for most mammals that are bipedal is waddling. In contrast, humans stride. Homo sapiens is special in this regard due to the fact that we are the only mammalian species adapted to stride bipedally. The earliest evidence of a bipedal hominin species is the Au. afarensis about 3.5 million years ago (Gruss, Tobias and Schmitt 2-9). In addition to the conclusions drawn from anatomical evidence, a trackway about ninety feet in length produced by three individuals, was discovered in Tanzania. Fragmental remains of the Orronin tugenensis discovered in Kenya have also been cited by experts to indicate bipedality. Ar. Ramidus which lived between 6 and 4.5 million years ago in present day Ethiopia were also shown to be bipedal . Some of the evidence that shows these species might have been bipedal, include similarity to humans in the placement of the hole in the cranium where the spinal cord enters. Further characteristics include a pronounced tarsal region with similar structures to later known bipedals.
The skeletal structures responsible for locomotion in species such as A. africanus which lived in the period between 3.5 and 2.5 million years ago and Paranthropus robustus which lived between 2 and 1.5 million years ago do not vary much from those of the above mentioned A. afarensis (Gruss, Tobias and Schmitt 2-9). While the skeletal structure of P. boisei is not very well known, there is little reason to presume that it is any different from the Paranthropus species. Homo habilis which existed in the period between 2 and 1.5 million years ago discovered in Olduvai Gorge in Tanzania, exhibited small sized teeth and a large cranial capacity, however, it had long limbs, especially forearms, shorter femurs, curved finger bones. These traits show a mixture of arboreal and bipedal movement. With the more recent species such as the Homo heidelbergensis which existed between 6 and 2 thousand years ago and the Neanderthals who existed 2 to 3 thousand years ago, while close to humans, they still have specific features that ring of the anatomy of the Australopithecus (Gruss, Tobias and Schmitt 2-9). Unfortunately, information regarding developmental foot structure of early Homo genus is not very scarce. The oldest footprints that attest to some bipedal locomotive functions were found in Ileret in Kenya and were dated to be made approximately 1.5 million years ago. These footprints suggested to experts that they belonged to Homo erectus (Gruss, Tobias and Schmitt 2-9). This implies that it is pragmatic to assume that around 1.5 million years ago, distinctly human motive structures were established.
Conclusion
From the discussion above, a retrospective look at the ancestry of humans, shows that the road to the modern day Homo sapien has been a very long one. This journey started millions of years ago. As seen, theoretically, when you go back through time, you would find out who exactly were the family of Homo sapiens that were the direct ancestors to the modern day humans. Go back even further, and you will find, the points at which the lineage of the humans meets that of the Neanderthals, then chimpanzees, early primates, mammals, and far back enough, even the earliest life forms! Of course this is not quite practically possible, due to the limitations in technology among other things. It is a mind boggling journey. It is therefore remarkable that scientists have been able to piece some of this evolutionary puzzle. When compared to earlier forms of our ancestors, modern day humans are so different yet so similar to our ancestors. We have gone takes leaps from residing in caves, to living in concrete structures many feet off the ground. We have gone from primitive and ignorant ways to landing on the moon and developing the internet. It is a true testament to the power of evolution!