Human Evolution

The journey of human evolution began approximately 85 million years ago during the Late Cretaceous period, when primates diverged from other mammals. However, the first true primates appeared around 65 million years ago.

Emergence of Primates (65-55 Mya)

This event marked the beginning of human evolution during the Paleocene Epoch. After the mass extinction event wiped out the dinosaurs, small tree-dwelling mammals evolved into primates. They had grasping hands, forward-facing eyes, and a large brain-to-body ratio. 

Fossil Evidence:

• Purgatorius (66-63 Mya) – Known to be one of the earliest known primates, they resembled a small, tree-dwelling mammal.
• Altiatlasius (57-55 Mya) – Considered a basal primate that showed early adaptations to arboreal life.

Evolution of Early Primates and Prosimians (55-40 Mya)

During this period, primates diverged into two major groups:

• Strepsirrhines (Wet-nosed primates), which include lemurs and lorises (Prosimians).
• Haplorhines (Dry-nosed primates), which include monkeys, apes, and humans.

They had grasping hands and feet with nails, forward-facing eyes with binocular vision, and increased brain size and shortened snouts. These primates were small and lived primarily in trees. 

Fossil Evidence:

• Teilhardina (55 Mya) – One of the earliest known haplorhines.
• Darwinius masillae (‘Ida’) (47 Mya) – A well-preserved fossil that shows characteristics of both early primates and more advanced monkeys.

Advent and Rise of Anthropoids (40-25 million years ago)

During this period, primates evolved from small, nocturnal, prosimian-like ancestors into larger, diurnal (day-active) primates with improved vision, greater intelligence, and more complex social structures. These higher primates, known as anthropoids, include primitive monkeys, apes, and humans. They diverged into two major groups: 1) New World monkeys (Platyrrhines) likely originated in Africa and later migrated to South America around 36-34 million years ago, and 2) Old World monkeys and Apes (Catarrhines) that evolved in Africa and Asia.

Anthropoids had larger brain sizes, enhanced vision, and could vocalize for communication. They started living in groups and developed dominance hierarchies. This phase witnessed a shift in the diet of those animals towards more frugivorous (fruit-eating) and omnivorous diets to survive in more diverse environments. 

This phase led to the foundation for the later evolution of apes and humans. 

Fossil Evidence:

• Eosimias (45-40 Mya) – One of the earliest anthropoid primates, showing characteristics of early monkeys.
• Aegyptopithecus (33 Mya) – It is a key transitional species between early primates and later Old World monkeys.

Evolution of Great Apes (15-10 Mya)

This phase (the Miocene Epoch) marked the evolution of large-bodied primates (the apes) with advanced cognitive abilities, complex social structures, and increased adaptability. These apes are the direct ancestors of modern gorillas, chimpanzees, bonobos, orangutans, and humans. They diversified into distinct lineages such as African, Asian, and European lineages.

Great apes possessed large-sized brains, shorter tails than their ancestors, had flexible locomotion, and started living in social groups.

Fossil Evidence: 

• Proconsul (22-17 Mya): Transitional species between early apes and great apes.
• Kenyapithecus (14-13 Mya): Early ancestor of African and Asian great apes
• Pierolapithecus (13 Mya): One of the earliest apes

Appearance and Divergence of Early Hominids (7 to 6 Mya)

This phase marked the divergence of hominins (human ancestors) from the common ancestor shared with chimpanzees and bonobos. They developed features of bipedalism, brain expansion, change in dentition, and complex social structures that separated them from other great apes.

One of the earliest hominins, Sahelanthropus tchadensis, displayed a mix of primitive ape-like features and early human characteristics, such as a flatter face and a skull adapted for bipedal walking. These adaptations started their shift from forested habitats to open savannas, where bipedalism provided advantages for foraging.

Another hominin group, Australopithecus, thrived around 4.2–2 million years ago, showed clear bipedal adaptation. Examples like Australopithecus afarensis (‘Lucy’) had the combined feature of upright walking together with the ability to climb trees. These features indicated a transitional phase between the arboreal and terrestrial lifestyles of this genus.

Fossil Evidence:

• Sahelanthropus tchadensis (7-6 Mya) – Displays both ape-like and human traits, including a skull adapted for bipedal walking.
• Orrorin tugenensis (6 Mya) – Shows evidence of early bipedalism in leg bones.

Genus Homo (2.4 Mya – 1.9 Mya)

Around 2.4 million years ago, the genus Homo emerged. They had greater cognitive abilities. Homo habilis, often known as ‘handy man,’ is credited with the earliest use of simple stone tools. They made use of these tools in cooking food, which provided them with the energy for brain development.  

The next significant step of evolution came with the appearance of Homo erectus around 1.9 million years ago. They had large brains, developed advanced tool-making skills, and could control fire. These advancements have allowed Homo erectus to migrate out of Africa into Asia and Europe. 

Fossil Evidence:

• Homo habilis (2.4–1.4 Mya) – Known as the ‘Handy Man,’ it was the first species to make stone tools.
• Homo erectus (1.9 Mya – 110,000 years ago) – Had a larger brain, controlled fire, and migrated out of Africa.

Evolution of Archaic Homo sapiens (600,000 – 40,000 Years Ago)

This era saw the emergence of Homo heidelbergensis, Homo neanderthalensis, and early Homo sapiens, forming a bridge between earlier hominins like Homo erectus and modern humans.

• Homo heidelbergensis – They were early humans that lived in Africa, Europe, and Asia.
• Homo neanderthalensis (Neanderthals) – They lived in Europe and adapted to cold climates.
• Early Homo sapiens – They were direct ancestors of modern humans.

Archaic Homo sapiens showed increased brain size, used more sophisticated tools, and showed early symbolic behavior (such as burying their dead).

Fossil Evidence:

• Homo heidelbergensis (600,000-200,000 years ago) – Considered a common ancestor of both Neanderthals and modern humans.
• Neanderthals (400,000-40,000 years ago) – Adapted to cold European climates and had a stocky build.

Modern Humans (~300,000 Years ago)

Homo sapiens, the modern humans, first appeared around 300,000 years ago in Africa. Fossil and genetic evidence suggest that early Homo sapiens populations initially thrived in small groups, relying on advanced tool-making, hunting strategies, and social cooperation for survival. Unlike their predecessors, modern humans have high cognitive abilities, can do abstract thinking, and have developed language for communication. 

Fossil Evidence:

• Jebel Irhoud fossils (300,000 years ago, Morocco) – Oldest known fossils of modern humans.
• Omo fossils (195,000 years ago, Ethiopia) – Early Homo sapiens with modern features.