A new variety of mammal branched off from its ground-dwelling ancestors about 55-85 million years ago to adapt to these dense canopies.
Evolutionary Developments:
Opposable Thumbs 🖐
Development of opposable thumbs and increased dexterity enabled primates to grip limbs while climbing and moving through trees.
Forward-Facing Eyes 👀
Offered better judgment of depth and distance when swinging from limb to limb. But less adept at detecting predators compared to the side-facing eyes of their predecessors, which offered greater peripheral vision.
With the global climate entering a prolonged drying period about 60 million years ago, savannas began to slowly overtake rainforest throughout the world. By about 4 million years ago, savannas made up much of the East African landscape.
The expansion of these grasslands and thinned-out woodlands forced many of the great apes out into the open in order to survive. This exerted further evolutionary pressure toward larger brains and increasingly complex social structures. It was in adapting to life in the open savannas that our ancestors began to walk upright.
Specialized use of hands and arms. Examples include being able to gather food with two arms and hands, craft tools and weapons, and throw projectiles.
Elevating the head for long-distance vision.
Less heat and sun exposure.
Caring for the young. Free hands allow parents to care for children while gathering larger quantities of food. Longer dependency equates to increased brain development.
Driving Evolutionary Factors:
Adapting to life on the savannas. Selection pressures favored bipedalism to better see over tall grass in search of predators and resources, to better reach fruit in trees, and to traverse greater distances in search of food and cover.
Started in rainforest habitats. There is evidence the trend toward bipedalism began before primates left the trees of the rainforests. As trees were in the process of thinning out, being partially bipedal would offer advantages in negotiating weaker branches.
Evidence suggests that human ancestor Australopethicus was fully bipedal by about four million years ago.
The first genus of hominid considered to be “human”.
➤ Australopithecus origin dates to about four million years ago.
➤ Likely the first human ancestor to become fully bipedal.
➤ Evidence indicates Australopithecus was the first to manufacture tools.
➤ Loss of body hair possibly began with Australopithecus.
Australopithecus's ancestral line will eventually produce Homo erectus around two million years before present, right around the time it becomes extinct. Homo erectus, a direct ancestor to Homo sapiens, will become the first human species to spread throughout Eurasia.
Approximate Territorial Range (Shaded)
➤ Direct ancestor to Homo sapiens
➤ First human species to venture out of Africa (around 2 million years ago)
➤ First human species to have a flat face and prominent nose
➤ Engaged in coordinated hunting of large-sized game
➤ Lost body hair and became dark skinned around 1.2 million years ago
➤ May have controlled fire as early as 1.5 million years ago
➤ Brain doubled in size compared to ancestral species
➤ Made hand axes which were chiseled on two sides to create a sharp edge
➤ Made simple shelters
➤ Took care of their disabled and ill
➤ May have used an early form of language
➤ Between 5' and 6' tall
➤ Robust build compared to Home sapiens
➤ Evolved to withstand cold weather
➤ Height and brain size comparable to early modern humans
➤ Sophisticated technology from use and control of fire, adhesives, clothing, seafaring, using plants as medicine, storing food and cooking
➤ Possibly capable of art and symbolic thinking
➤ Likely extinct by about 30,000 years ago
➤ Interbred with Homo sapiens before going extinct
Denisovans
➤ Sparse fossil record suggests Denisovans were very similar to Neanderthals in almost every way, physically and behaviorally
➤ Likely extinct by about 20,000 years ago
➤ Like Neanderthals, also interbred with Homo sapiens before going extinct
Homo Sapiens in Africa Became Behaviorally Modern Between 100,000 and 50,000 Years Ago
Several waves of human species migrated out of Africa over the course of tens, and even hundreds, of thousands of years. Each was more advanced and dominant than the one that came before. In every case, the version of human migrating from Africa outcompeted and displaced those human species that had long established themselves in the lands beyond. But why was it never the other way around? While we can only speculate, it could have something to do with the fact that there has always been greater genetic diversity among human populations in Africa compared to elsewhere. This remains true to this day. And why is that? The answer is likely to be found in the very reasons Africa became the birthplace of the human family of species to begin with. From the rainforests that once thrived there to the savannas that would eventually become prevalent, Africa proved to be the perfect breeding ground for this particular type of upright-walking, deep-thinking mammal that would take over the planet. Whatever the precise reasons, Africa’s role in the rise of humankind is undeniable. Every creative conception, every ground-breaking innovation, every elevated sense of a higher truth and beauty beyond the scope of everyday experience—all of it traces back to the land where our original forebearers took their first steps.