Journey Through Human Evolution

Evolutionary Process Leading to Anatomically Modern Humans:

• Human evolution is the process that led to the emergence of Homo sapiens as a distinct species of the hominid family, which includes all the great apes.

• Primates diverged from other mammals about 85 million years ago (mya), with their earliest fossils appearing over 55 mya, during the Paleocene.

• Hominids (a tribe of the African hominid subfamily) gradually developed traits such as human bipedalism, dexterity, complex language, and interbreeding with other hominins.

• The earliest known catarrhine is Kamoyapithecus from uppermost Oligocene at Eragaleit in the northern Great Rift Valley in Kenya, dated to 24 million years ago.

• The Homo genus is evidenced by the appearance of H. habilis over 2 mya, while anatomically modern humans emerged in Africa approximately 300,000 years ago.

• The genus Australopithecus evolved in eastern Africa around 4 million years ago before spreading throughout the continent and eventually becoming extinct 2 million years ago.

• The earliest documented representative of the genus Homo is Homo habilis, which evolved around 2.8 million years ago and is arguably the earliest species for which there is positive evidence of the use of stone tools.

• During the next million years, a process of rapid encephalization occurred, and with the arrival of Homo erectus and Homo ergaster in the fossil record, cranial capacity had doubled to 850 cm3.

• Modern humans evolved in Africa possibly from H. heidelbergensis, H. rhodesiensis, or H. antecessor and migrated out of the continent some 50,000 to 100,000 years ago.

• Recent DNA evidence suggests that several haplotypes of Neanderthal origin are present among all non-African populations, and Neanderthals and other hominins may have contributed up to 6% of their genome to present-day humans.

• The transition to behavioral modernity with the development of symbolic culture, language, and specialized lithic technology happened around 50,000 years ago.

• H. habilis made tools from stone and perhaps animal bones, leading to its name homo habilis (Latin 'handy man') bestowed.The Evolution of Homo Species

• Homo habilis is the earliest known human species and lived from about 2.8 to 1.5 million years ago.

• Homo erectus lived from about 1.8 million years ago to about 70,000 years ago and is considered a separate species from Homo ergaster, which is a subspecies of Homo erectus.

• Homo heidelbergensis lived from about 800,000 to about 300,000 years ago.

• Homo neanderthalensis lived in Europe and Asia from 400,000 to about 28,000 years ago and interbred with anatomically modern humans.

• Homo floresiensis lived from approximately 190,000 to 50,000 years before present and is nicknamed the hobbit for its small size.

• There is ongoing debate over whether Homo floresiensis is a separate species or a modern Homo sapiens with pathological dwarfism.

• In 2019, scientists reported the computerized determination of a virtual skull shape of the last common human ancestor to modern humans/H. sapiens.

• The trend in intra-cranial volume expansion and the elaboration of stone tool technologies developed between 400,000 years ago and the second interglacial period in the Middle Pleistocene, around 250,000 years ago, providing evidence for a transition from Homo erectus to Homo sapiens.

• H. sapiens interbred with archaic humans both in Africa and in Eurasia, notably with Neanderthals and Denisovans.

• The most significant adaptations of human evolution are bipedalism, increased brain size, lengthened ontogeny, and decreased sexual dimorphism.

• Bipedalism was one of the most significant morphological changes in human evolution and first occurred in Homo erectus.

• The relationship between the changes in human evolution is the subject of ongoing debate.Evolution of Humans: Key Points

• Bipedalism is the basic adaptation of hominids and is considered the main cause behind a suite of skeletal changes.

• The earliest hominids to exhibit primitive bipedalism are Sahelanthropus or Orrorin, both of which arose 6 to 7 million years ago.

• Bipedalism freed the hands for reaching and carrying food, saved energy during locomotion, enabled long-distance running and hunting, provided an enhanced field of vision, and helped avoid hyperthermia.

• Anatomically, the evolution of bipedalism has been accompanied by a large number of skeletal changes, including the shape of the big toe, the femur, knee and ankle joints, and the pelvic region.

• Encephalization, the increase in brain size, began with Homo habilis and continued through Homo erectus and Neanderthals.

• Humans have a reduced degree of sexual dimorphism, visible primarily in the reduction of the male canine tooth and reduced brow ridges and general robustness of males.

• Ulnar opposition, the contact between the thumb and the tip of the little finger of the same hand, is unique to the genus Homo, including Neanderthals and anatomically modern humans.

• Other changes include the reduced reliance on smell, a longer juvenile developmental period, a smaller gut and small, misaligned teeth, loss of body hair, evolution of sweat glands, and a descended larynx.

• The use of tools has been interpreted as a sign of intelligence, and it has been theorized that tool use may have stimulated certain aspects of human evolution.

• The transition to behavioral modernity has been characterized by some as a "Great Leap Forward" or as the "Upper Palaeolithic Revolution".

• Evidence of behavioral modernity exists from Africa, with older evidence of abstract imagery, widened subsistence strategies, more sophisticated tools and weapons, and other "modern" behaviors.

• The immediate survival advantage of encephalization is difficult to discern, but it has been suggested that the changes were mainly social and behavioral.

• The emerging field of cultural evolution studies human sociocultural change from an evolutionary perspective.A Brief History of Human Evolution

• Modern humans evolved in Africa around 300,000-200,000 years ago, before spreading to other parts of the world.

• The Australian Aboriginal population separated from the African population around 75,000 years ago, and made a 160 km sea journey 60,000 years ago.

• Modern humans started burying their dead, making clothing from animal hides, hunting with more sophisticated techniques, and cave painting.

• Different populations innovated existing technologies, which had not been seen prior to 50,000 BP.

• Anatomically modern human populations continue to evolve, as they are affected by both natural selection and genetic drift.

• Some traits, such as resistance to smallpox, have decreased in selection pressure, but humans are still undergoing natural selection for many other traits.

• Particularly strong selective pressures have resulted in high-altitude adaptation in humans.

• Culturally-driven evolution can defy the expectations of natural selection.

• Menopause is evolving to occur later, and there are other reported trends such as lengthening of the human reproductive period and reduction in cholesterol levels, blood glucose and blood pressure in some populations.

• Africa is considered as the cradle of humankind, with many early hominid fossils found there.

• The genetic revolution in studies of human evolution started when Vincent Sarich and Allan Wilson measured the strength of immunological cross-reactions of blood serum albumin between pairs of creatures, including humans and African apes.

• Human dispersal out of Africa has occurred at least three and possibly four times.