About 700 million years ago, the basic chemicals in the earth’s atmosphere, namely – Hydrogen and Carbon combined to form life in the water. This slowly evolved into primitive water plants. They began to grow and occupy the shallow and warm seas. The water plants gradually adapted themselves and began to encroach on to the land. About 500 million years ago, Protozoa originated in water. 

It is considered to be the first form of animal life. Then single-cell beings became multicellular. The primitive life forms like photosynthetic bacteria released oxygen into the atmosphere as they evolved, which made earth more habitable for higher life forms to originate.

Water creatures appeared. Insects and Amphibians came into existence. The Amphibians were capable of existing on land and water as well. Then the reptiles appeared and some of the species among them adapted to become birds. All this diversified life forms took about 400 million years to evolve.

Mammals evolved about 200 million years ago. Horses, Camels, Dogs, etc. evolved around 50 million years ago. Primates made their appearance 36 million years ago. Hominoids evolved and human-like creatures came upon earth’s surface about 5.6 million years ago.

1. The super family Hominoidea branched into Hominidae and Hylobatidae families. The • species of the respective families are called Hominids and Hylobatids. The Hominids, that is, Humans, Chimpanzees and Bonobos, Gorillas and Orang-utans, diverged away from the Hylobatids that is Gibbons.

2. The Hominidae family branched into Homininae and Ponginae subfamilies. The species of the respective subfamilies were called Hominines and Pongines. The Hominines that is, Humans, Chimpanzees and Bonobos and Gorillas diverged away from the Pongines that is the Orang-utans.

3. The Homininae subfamily branched into Hominini and Gorillini tribes. Humans, Chimpanzees, and bonobos branched away from the Gorillas.

4. The Hominini tribe branched into Genus Homo and Genus Pan. That is, the ancestral human species branched away from the Chimpanzees and the Bonobos. As such, Chimpanzees and Bonobos are the closest relatives of the Humans.

The evolution of genus Homo from the super family Hominoidea took about 30 million years. The emergence of genus Homo brought humanlike creatures on the earth’s surface about 5.6 million years ago. Today we are living in a time that is relatively warm compared to the last 6 to 8 million years.

The weather and climate of the earth has played an important role in the origin and evolution and the existence of various species. Human species evolved larger and complex brains to overcome the environmental challenges and survive against physically powerful animals.

The size of the brain in the Homo habilis was 600 cubic centimeters, which was only slightly larger than that of Chimpanzees. The homo Erectus had a brain size of 800 -1100 cc, the Neanderthal 1200 -1900 cc and the Homo sapiens (wise man) of today about 1400cc.

It is more than twice the size of the brains of Chimpanzees or Gorillas. The growth in the brain size induced many activities like improved vision, upright posture, bipedalism, toolmaking, use of fire, planned and skilled hunting, storing food and language. 

These activities helped in the development of the brain. Hominoids lived on trees which provided them protection from the predators. The Hominoids were food gatherers and not meat-eaters. Then, they adapted to land-dwelling. They began to use caves and extended stone boulders as shelters. The Neanderthal man was the earliest cave dweller. The shortage of food made them to scavenge for food.

The above activities made them gradually develop an upright posture and consequently the bipedal motion. This was required for survival. Hominines and the archaic human species added planned hunting and fishing to the already existing gathering, foraging, and scavenging techniques. The earliest evidence of planned hunting and butchery of large animals is traced to two sites.

1. Box grove in England dated to about 50,0000 years ago 

2. Schoningen in Germany dated to about 4,00,000 years ago. 

The Hominoids were quadrupeds. They walked on all four limbs, but, their forelimbs were flexible. The Hominids gradually adapted an upright posture. Hominines further adapted to bipedalism. The skeletal structure and the muscles also adjusted over a period of time to the upright posture and the bipedal motion, which freed the forelimbs.

The forelimbs developed precision grip and power grip and evolved into hands. This greatly helped in hunting and defending from predators as hands could be used to make tools and also use them. Walking on two legs also provided a greater long-distance vision and helped them to cover long distances without spending much energy.

Place of Origin of the Humans.

The place of origin of the humans or modem man is a much-debated issue. There are two divergent theories.

1. The Replacement or African origin Theory 

2. The Regional Continuity theory.

Replacement or African origin theory: According to this theory, the modern human species evolved from the archaic species in Africa. Africa with its nurturing tropical climate consisting of strong wet and dry seasons provided an optimum environment for the emergence of modern human species.

The Regional continuity theory: According to this theory the evolution of different human species from the earlier species occurred in all regions of the world. It occurred in Europe and Asia also, as it occurred in Africa.