Human Evolution First primates appeared about 55 million years ago they were adapted to an arboreal life (tree-dwelling): 1. five grasping digits – including an opposable thumb or toe 2. nails instead of claws to protect the tips of the digits 3. fleshy pads at the ends of the digits that are sensitive to touch 4. long slender limbs that rotate freely at hips and shoulders

5. large, forward-looking eyes located in front of the head to provide stereoscopic (three-dimensional) vision fields of view overlap allowing the ability to accurately judge distances (important when jumping from branch to branch) stereoscopic vision has been associated with a flattening of the face 6. reduced sense of smell and relatively small nose – shorter nose is associated with flat face and stereoscopic vision

7. unspecialized digestive system – can exploit large range of food sources 8. reduced number of offspring – females usually bear one young at a time and the baby is helpless and requires long period of nurturing - young cling to mother 9. relatively large brain size – increased sensory input associated with sharp vision and greater agility favored larger brains 10. social groupings – all primates live to some degree in a social group

Modern primates are divided into two subgroups: Prosimii (prosimians – meaning “before the ape), includes lemurs, lorises, pottos, and tarsiers Anthropoidea (anthropoids) include monkeys, apes, and humans

Anthropoid primates arose at least 45 million years ago in Africa or Asia Anthropoids have larger brain sizes compared to other primates

Monkeys are divided into two groups: New World and Old World monkeys New World Old World

Old World monkeys are found in tropical parts of Africa and Asia: monkeys differ from apes by having tails and forelimbs that are not usually longer than the hindlimbs New World monkeys are found in Central and South America – arboreal, and some have prehensile tails (wraps around branches and serves as fifth limb) Old World monkeys are found in tropical parts of Africa and Asia: most are arboreal though some are ground-dwellers (these are quadrupedal – walk on all fours) none have prehensile tails group from which apes and humans are thought to have evolved

Old World monkeys shared a common ancestor with the hominoids, group consisting of apes and hominids (humans and their ancestors) In addition to monkeys, the anthropoid suborder also includes four genera of apes: Hylobates (gibbons), Pongo (orangutans), Gorilla (gorillas), and Pan (chimpanzees and bonobos)

modern apes (gibbons, gorillas, orangutans, and chimpanzees) are our closest living primate relatives – humans and chimpanzees have a common ape-like ancestor and share very similar DNA Brachiation (gibbons and orangutans) – movement through trees by arm-swinging hand over hand Knuckle-walking (chimpanzees, bonobos, gorillas) – have adapted to life on the ground – quadrupedal walking in which they fold their digits when moving Brachiation, Knuckle-walking, and the absence of a tail are thought to have been a preadaptation to bipedalism (walking on two legs)

Hominid Evolution Early hominids adopted a bipedal posture Differences in human skeleton and skull compared to the ape skeleton indicate a habitat change for early hominids from an arboreal existence to life spent partly on ground Curvature of human spine provides better balance for bipedal locomotion human pelvis is shorter and broader allowing for better attachment of muscles for walking

foramen magnum is centered in the skull base compared to being located in the middle rear of the skull in apes alignment of big toe with other toes

Other trends in hominid evolution: increase in size of brain relative to the size of the body supraorbital ridges lacking in modern human skulls (prominent bony ridges above eye sockets) human faces are flatter and jaws are different from apes teeth are arranged differently in humans and are smaller in size

Trends in Hominid and Human Fossils

Hominid Evolution Hominid evolution began in Africa Ardipithecus ramidus lived approx. 5.8 million to 4.4 MYA in Ethiopia Believed to be very close to split between the line that led to human-like organisms and line that led to chimpanzee-like organisms Most fossils of this species are teeth so difficult to be sure about physical features Probably similar to chimpanzees but canines were more hominid-like Possibly bipedal

Australopithecines Most paleoanthropologists recognize at least 6 species The genus Australopithicus contains the immediate ancestors of the genus Homo Name means “southern man ape” Had shorter legs, longer arms, and smaller brains relative to modern humans Australopithecus anamensis Existed 3.9 to 4.2 million years ago Discovered and named by Leakey in 1995 in East Africa Appears to have been bipedal

A. afarensis was bipedal, but probably did not use tools or fire Australopithecus afarensis may have arisen from A. anamensis about 2.5-4 MYA famous fossil “Lucy” is A. afarensis (found in Ethiopia in 1974) – about 40% complete fossil A. afarensis was bipedal, but probably did not use tools or fire Had a taller jaw Fairly large molar teeth Projecting face Cranial capacity: 380 – 430 cm3

A. afarensis possibly gave rise to both Australopithecus africanus and other australopithecines Australopithecus africanus appeared about 2.5 - 3 MYA walked erect human-like hands and teeth ate both plants and animals had a small brain more like that of primate ancestors than of present-day humans (435 – 530 cm3) Tall, thick lower jaw and large molars Projecting face

Homo habilis is the oldest member of the genus Homo Lived 2.5 – 1.6 MYA first hominid to have enough human features to be placed in genus, Homo small hominid with larger brain (600 cm3), smaller teeth, and flatter face than australopithecines H. habilis used primitive tools Relationship between H. habilis and australopithecines is unclear

Homo habilis

Homo erectus Homo erectus apparently evolved from Homo habilis H. erectus appeared in Africa about 1.8 MYA, then spread to Europe and Asia Lived as recently as 100,000 years ago Peking man and Java man are examples of Asian H. erectus dated at 200,000 years ago H. erectus was taller than its ancestors, had a larger brain (1000 cm3), and smaller jaw Had receding forehead, large brow ridges and smaller molars

Homo erectus H. erectus used more advanced tools (Archeulian tools), wore clothes, used fire, lived in caves or shelters, and hunted and scavenged for food

H. erectus fossils may actually represent two species – H H. erectus fossils may actually represent two species – H. erectus and H. ergaster some researchers suggest that H. ergaster was an earlier African species, and H. erectus was a later eastern Asian offshoot these researchers believe that H. ergaster led to modern humans and H. erectus became and evolutionary dead end

Archaic Homo sapiens appeared about 800,000 years ago descendants of Homo erectus or Homo ergaster that lived in Africa, Asia, and Europe they overlapped both Homo erectus populations and the later appearing Neandertals some researchers classify archaic Homo sapiens as a separate species, Homo heidelbergensis

Neandertals Neandertals appeared approximately 200,000 – 30,000 years ago first discovered in Neander Valley in Germany lived throughout Europe and western Asia short, sturdy builds, faces projected slightly, chins and foreheads receded, had heavy brow ridges and jaw bones, brains (1600 cm3) and front teeth were larger than modern humans

Neandertal

much debate exists about whether the Neandertals are a separate species from modern humans or a race of Homo sapien many researchers believe that anatomical differences between Neandertals and modern humans indicate that they were separate species – Homo neanderthalensis and Homo sapien tools included oldest known spear points (known as Mousterian tools) – more sophisticated than those of H. erectus existence of skeletons of elderly Neandertals and of Neandertals with healed fractures demonstrates that they cared for aged and the sick – indication of advanced social cooperation had rituals and buried their dead

disappearance of Neandertals about 30,000 YA is not well understood humans with more modern features coexisted with Neandertals for tens of thousands of years Neadertals may have interbred with modern humans, diluting their features beyond recognition (however, analysis of mitochondrial DNA from Neandertal bone seems to indicate that Neandertals were an evolutionary dead end) possible that more modern humans out competed the Neandertals

Origin of modern Homo sapiens is subject to much debate Modern Homo sapiens dates back to 140,000 – 70,000 years ago in Africa, Europe, and Asia H. sapiens skull lacked heavy brow ridge and possessed a distinct chin, high forehead, flat face, small molars, and very small jaw Cranial capacity about 1300 cm3) Homo erectus Homo sapiens

Cro-Magnon culture in France and Spain typifies the early H. sapiens weapons and tools were complex and made of materials other than stone (bone, ivory, wood) developed art, including cave paintings, engravings and sculpture sophisticated tools and art indicate that they may have possessed language

Cro-magnon

Possible Coexistence of Several Hominid Species Some hominid species existed on Earth at the same time Overlap in fossil ages is present in: A. afarensis and A. africanus – approx 3 MYA H. erectus, H. neanderthalensis, and H. sapiens – approx. 100,000 years ago

Did these species interact? Very few Australopithecines, so possible they never met each other but coexisted for a million years so there was time for chance encounters There is evidence that H. neanderthalensis and H. sapiens probably interacted but probably did not produced fertile offspring (according to IB!) World population was only in the tens of thousands and the presence of a mountain range or wide river could have prevented populations from encountering each other

Uncertainties about Human Evolution Many gaps and questions in human evolution timelines Fossil record is incomplete – most bodies are decomposed and don’t leave behind a fossil or fossils degenerate over time – as a result, difficult to determine how different species of hominid are related Most hominid fossils are limited to bones and teeth Difficult to estimate cranial sizes because of differences between males, females and juveniles

Changes in Brain Size during Hominid Evolution Although there are numerous advantages to having a larger brain, there are disadvantages too: Require more energy – need more foods that are rich in energy and protein in diet Hominids got additional energy by adding more meat to diet Earliest hominids were foragers and ate fruits and nuts To eat meat on a regular basis, needed a more complex social system to allow for cooperative hunting As tools became more sophisticated, hunting techniques improved and availability of high-protein foods increased Large quantities of animal bones found at fossil sites suggest that meat was important to the early human diet More protein led to larger brains which lead to increase in complexity of tools which led to better hunting so more protein in diet etc… Cooking food increases digestibility – a certain degree of intelligence and relatively large brain needed to control fire and cook food

In the evolution of hominids, there is a general trend showing an increase in cranial capacity

Two opposing hypotheses exist about the origin of modern humans: 1. “Out of Africa” hypothesis – states that modern humans arose in Africa and then migrated to Europe and Asia, displacing the more primitive humans living there

2. “multiregional” hypothesis – states the modern humans originated from Homo erectus as separately evolving populations living in several parts of Africa, Asia, and Europe each population evolved in its own distinctive way but occasionally met and interbred with other populations, thereby preventing complete reproductive isolation

Humans have undergone Genetic and Cultural Evolution Genetic evolution – deals with inherited characteristics: Physical characteristics (brain size, bipedalism) Number of chromosomes Particularities of biochemicals such as blood proteins Cultural evolution – deals with acquired knowledge that can be passed within a social group and through generations: Language (spoken and written) Customs and rituals (burying the dead) Art Technology (obtaining food, warfare)

Importance of Genetic and Cultural Evolution One way to measure the culture of a people is to look at the quality and complexity of their artifacts (tools and artwork) Species Example of Culture Tools Developed H. habilis Oldowan Simple choppers, scrapers and flakes of rock H. erectus Acheulian Hand axes, cleavers and picks H. neanderthalensis Mousterian Large flakes of uniform size produced from a core then trimmed to the desired tool H. sapiens Soultrian Delicate blades for knives, drills Other materials added (bone, antler, and ivory Some tools are ceremonial

As brain size increased so did quality of tool-making There is a connection between genetic and cultural evolution Genetic evolution probably occurred first because need larger brain size to develop more sophisticated tools In the last 30,000 years, H. sapiens evolution has been largely cultural, not genetic Cro-Magnon man is physically the same as humans today Since the Upper Palaeolithic period (40,000 – 10, 000 years ago), human culture has developed exponentially Cultural evolution sometimes lags behind genetic evolution Our current cranial capacity has existed for 140,000 years but major cultural advances do not appear until 35,000 years ago Cultural evolution has potential to revolutionize a human population much more quickly than genetic evolution H. sapiens has been able to evolve culturally far more than any of our ancestors without any major genetic evolution