What is meant by Human Evolution?

Human evolution is the process of evolution of humans from early man to anatomically modern humans. The process of evolution in humans leads to the gradual development of traits like bipedalism. Humans are the highly social animals that make them the most advanced animal on Earth.  Human evolution is an outcome of interaction among the following processes:

• Mutation
• Genetic recombination
• Natural selection
• Reproductive isolation
• Chromosomal abnormalities 

Stages in Human Evolution

The evolution of humans has undergone the following stages:

1. Dryopithecus

They are assumed to be the oldest common ancestor of man and apes from the evolutionary perspective. It is a genus of extinct great apes that are referred to as oak wood apes. The Dryopithecus inhabited India, Europe, Africa, and China and lived around 12.5 to 11.1 million years ago. They had hairs throughout the body and looked more like apes and chimpanzees as compared to humans.

2. Ramapithecus

It is a genus of extinct primates thought to have lived around 12-14 million years ago. The fossils of Ramapitheucs were found in the Shivalik range in Punjab, and Africa, and Saudi Arabia. They are thought to have lived in open grasslands. The members of this genus had robust jaws and short canines, and they used their hands to eat the food. They are the small-bodied ancestors.

3. Australopithecus

This genus consists mainly of early hominin species mainly found in southern, north-central, and Eastern Africa. Some of the important characteristics of this genus are:

• Australopithecus lived for about 3.9-2.9 million years during the Late Pliocene and Early Pleistocene, as deduced from the evolutionary study.
• They have traits that are similar to apes and present-day humans. The Australopithecus were bipedal, the characteristic resembling the present-day humans, whereas the small size of their brain is similar to apes.
• Their brain was only 35% of the modern-day humans. They mainly lived arboreally (on trees). The first fossil was discovered in 1924 from South Africa, and thus they are also known as "Southern apes".
• "Lucy" is the famous fossilized specimen of Australopithecus discovered from Ethiopia.

4. Homo erectus

It is the most long-lived species of the genus "Homo". The H. erectus is believed to be the ancestor of present-day Homo sapiens. Some of the characteristics of H. erectus are: 

• Homo erectus lived approximately between 100,000 and 1.6 million years ago.
• They were the first man to leave Africa and the first ones to know the multiple uses of fire.
• The H. erectus is known by various names in different parts of the world. In Africa, they are known as Turkana Boy; in China, they are known as Peking Man; in Indonesia, they are known by the name "Java Man".
• According to the recent single-origin hypothesis, Homo erectus migrated out of Africa and originated into Homo sapiens.
• They are the first known hunter-gatherers.

5. Homo neanderthalensis

The Neanderthals are the extinct species of the genus Homo and are considered the closest extinct human relative as per the genetic sequence similarities. These were also known as Pithecanthropus erectus. They lived approximately 200,000 years ago during the Pleistocene Epoch. The first fossil of H. neanderthalensis was discovered from the Neander Valley in Germany; hence they are referred to as "Neanderthals'. They were thought to have lived from Europe to Asia are also known as "caveman". The characteristics of Homo neanderthalensis are:

• Neanderthals lived approximately at the same time as Homo sapiens.
• Neanderthals were good hunters and believed to be meat-eaters.
• Neanderthals knew the use of different tools efficiently and were able to make new tools.
• Neanderthals were vegetarian too. A scientist has found starch grains on the molar teeth of these humans.
• Neanderthals had a more robust build as compared to modern humans.
• The limbs of Neanderthals were shorter than modern humans.
• Neanderthals were able to live in low-temperature conditions.
• Neanderthal's genome project performed in 2010 provided evidence of the interbreeding between modern humans and Neanderthals.

6. Homo sapiens

Homo sapiens is unique from other extinct humans as they have the highest intelligence. They are known as modern humans. Their intelligence allows them to solve complex problems and think abstractly. Humans can also find the reason behind a problem and utilize their initial experiences to deal with different situations. The "sapiens" word means "intelligence". The important characteristics of Homo sapiens are following:

• Homo sapiens is the scientific name for modern humans, first given by Carolus Linnaeus, the father of modern biological classification.
• Modern humans emerged in Africa around 300,000 years ago from Homo heidelbergensis.
• Modern humans could use multiple and diverse types of tools.
• Homo sapiens can use language to communicate with each other.
• Homo sapiens can perform sexual reproduction that allows them to increase the genetic variation among them.
• Their average life span is approximately 70-80 years.
• Modern humans can learn new things and pass the teachings to their offspring.
• Homo sapiens are omnivorous. They can eat both plants and animals.
• Homo sapiens develop new techniques of arts and culture along with the passing of their techniques to new generations.
• The average height of modern humans ranges between 1.45 meters to 1.80 meters.
• The posture of the present-day man is erect. The spine allows the man to lift heavy weights and run at a different speed.
• The vision of modern-day humans is frontal.
• The hand consists of four fingers and one opposable thumb.

Some other important stages of human evolution

• Homo floresiensis was an early species of the genus Homo.
• Homo floresiensis lived on the island of Flores until modern humans arrived.
• Homo floresiensis is considered a sister species to Homo habilis.
• Homo habilis is considered the ancestor of Homo erectus.
• Homo heidelbergensis is considered a subspecies of Homo erectus.
• Homo Heidelbergensis lived during the Middle Pleistocene. 

Similarities between Humans and Early Primates

• Prehensile hands and feet are present in both humans and primates.
• Both have opposable thumbs.
• Both have great toes and flattened nails.
• The genome and mitochondrial sequence similarity between humans and primates are 99%. The modern human genome is 99% similar to a chimpanzee. Thus, it can be concluded that chimpanzees are human-like.

Differences between Humans and Early Primates

• Modern humans are more evolved among all primates.
• Humans are more social as compare to early primates.
• Humans have large brains and are more intelligent.
• Humans show more respect to cultural, religious, and philosophical beliefs.

Contribution of Haile-Selassie in Studying Human Evolution

Professor Yohannes Haile-Selassie is one of the renowned scientists of Africa working in the field of human evolution. Although he is involved in various projects related to human evolution, he complains that it is difficult for a well-qualified African researcher to get the necessary financial backing from the Western-based research funding organizations. He was involved in discovering the 3.8 million old skulls of an early ape-like human ancestor in Ethiopia. He published this finding in the "Nature" journal. He was also involved in discovering an ape-like human ancestor called Australopithecus anamensis, the oldest known Australopithecus. According to him, the direct ancestor of present-day humans is yet to be discovered.

Context and Applications

This topic is significant in the professional exams for both undergraduate and graduate courses, especially for:

• Bachelors of Science in Biology: Humans are intelligent animals on the Earth. Therefore, studying the evolution of humanity is important as it touches several aspects of human nature, such as the development of cognitive abilities, changes in the human body's defenses, and much more. The students can also study evolutionary biology.
• Master of Science in Biology: For post-graduate students, the study of human evolution is required to learn about the processes of scientific inquiry. For example, the coronavirus disease of 2019 (COVID-19) virus is also an example of the evolution of the virus. The students can also study evolutionary biology.