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Human Evolution: A Brief Overview, Stages and Timeline

The study of evolution is one that scientists and researchers have been carrying out for the last few centuries, with the biggest pioneer in the field of evolution being the English scientist Charles Darwin, whose concepts such as natural selection helped form the basis for the theory of evolution as we know it today. In simple terms, evolution refers to “the process by which new species or populations of living things develop from pre-existing forms through successive generations”, as defined by Merriam Webster. The changes characterizing evolution do not occur in any particular individual alone- these changes that are beneficiary for one’s survival are passed onto the offspring and so on to a whole population. This article seeks to look at human evolution in particular, and give a general overview of the same in layman terms.

What is Human Evolution?

Human evolution refers to “the process by which human beings developed on earth from now-extinct primates” (Tuttle, 2020). The subject of human evolution in of itself is so vast that there is a separate section of scientific study dedicated to it known as Palaeoanthropology. It is a subsection of anthropology wherein scientists seek to investigate the origins of our species and human behaviour by studying human fossils.

human evolution stages

Something that many may not know is that Homo sapiens, i.e human beings are one of many species that come under the genus Homo, with other species before us including Australopithecus afarensis, Homo erectus, and Homo habilis amongst others. There are an estimated 15 to 20 such species under the category of early humans.  The feature that distinguished hominids (our early ancestors) from other apes is that of the ability to walk on two feet, known as bipedalism, which developed over 4 million years ago. Human beings, chimps and gorillas share a common ancestor with chimps and bonobos being our closest relatives however the chimp-human lineages split around 7 and a half million years ago. Fossil and genetic evidence both suggest that humans originated in Africa, with all fossils of early humans (lived between 2-6 million years) having been found there.

There are different ways in which researchers have mapped out the stages of human evolution. Stages of evolution can be grouped in different sections therefore there can be four or five or son depending on how they have been arranged. Here we are looking at four main stages of evolution, arranged from the earliest species to the most recent:

  1. Stage one – between 4-7 million years ago: Sahelanthropus, Orrorin and Ardipithecus all appeared between this time period, and they are known as proto-hominins since it is debated whether they are our ancestors or not. They may have been bi-pedal.
  2. Stage two -around 4 million years ago: The genus Australopithecus, our ancestors who are also bipedal appeared then, found in both East and West Africa.
  3. Stage three – Around 2.7 million years ago: This is marked by the appearance of species classified under Paranthropus, however, it is unsure whether this classifies as a separate genus since amongst paleoanthropologists many classify it as a subsection of the Australopithecus genus.
  4. Stage four – Between 2.5-1.8 million years ago: This stage consists of the appearance of species that all fall under the genus Homo, which as mentioned before consists of us and our immediate ancestor species. Homo habilis, the oldest is characterized by the usage of stone tools and a chimpanzee sized brain. Homo erectus and Homo egaster, the following members had double the brain size and were able to control fire and use relatively advanced Then came along Homo heidelbergensis about 800,000 years ago and finally Homo sapiens appeared approximately 200,000 years ago. Some of the main traits or features that helped build modern human society – such as culture and symbolic language are ones we acquired 50,000 years ago.

Another angle of approaching it is looking at the four important steps, or rather four important traits that were involved in the making of modern humans. They are:

  1. Terrestriality: This refers to the adaptation of living on land (terrestrial).
  2. Bipedalism: As has been mentioned above already, this refers to the ability to walk on two feet. This helped tremendously as now hands could be used for other labour, long-distance travelling became easier, lesser sun exposure, etc. It also resulted in changes to body parts and changes in bodily processes such as gestation.
  3. Encephalization: An evolutionary adaptation involving an increase in the size of the brain and complexity. This increased the possibility for social learning and learning of languages.
  4. Civilization: A society that is characterized by advanced cultural and social development, and the making of tools is one such example that is regarded as indicative of evolution.

Other evolutionary adaptations of human beings include reduced differences between male and female sexes (sexual dimorphism), lesser body hair, a hidden estrus (no physically perceptible sign of fertility), etc.

Hypotheses surrounding early human evolution:

There are a couple of hypotheses that have been formed regarding the evolution of early humans – let us look into some of them. The savannah hypothesis suggested that hominins became bipedal as they had to adapt to the savannah after being forced out of trees and thus began walking erect using only their feet. The aridity hypothesis developed this further to state that evolution also occurred due to an increase in aridity and expansion of the savannah. The turnover pulse hypothesis looked into the role that climate and environmental change played and suggested that it led to a higher rate of evolution amongst specialist species and the spreading out of generalist species (as they can grow even with environmental changes).

The study of human evolution is one that is ongoing, not just because evolution is an ongoing process but also because there is still a lot that is unknown and that is being analysed and explored regarding both our origins as a species, our ancestors and our recent evolution, with studies coming out often containing new findings.