Stages in hominin evolution

Vs.

Africa

The Rift Valley is a long and thin fracture depression, with numerous volcanoes, which extends from the south of Turkey to East Africa and Mozambique. The great volcanic activity during the Pliocene (5-25 Ma) --numerous ashes and tuffs can be analyzed by means of the K/Ar method to determine their age.

• Prehumans • Between 10 and 4 million years–(e.g. Tchadensis (7m) and Ardipithecus ramidus (4m)) – Share an erect posture – double locomotion (Ardipithecus ramidus) – low degree of sexual dimorphism • 4 to 5 million years ago-humans and chimpanzees (our closest genetic relative) split off from a common ancestor Sahelanthropus tchadensis

https://australianmuseum.net.au/learn/science/human- evolution/sahelanthropus-tchadensis/ •Human-line diverged from the ape-line. •6-7 My •2001 discovery •Ape-like: Small brain (slightly smaller than a chimpanzee’s), sloping face, very prominent browridges, elongated skull. •Human-like: small canine teeth, a short middle part of the face, and a spinal cord opening underneath the skull instead of towards the back as seen in non- bipedal apes. Toumaï

Ardipithecus ramidus Name: local Afar language. ‘Ardi’ - ‘ground’ or ‘floor’ and ‘pithecus’ -- -‘ape’. ‘ramid’ -‘root’. •Position as a direct ancestor of humans is unclear. •Earlier assigned to Au. •Ancestral to Australopithecus or not??? •Wooded savanas • and upright posture •Modern chimpanzees and bonobos like: 4.5 Ma-old remains of •300-350cc, similar in body shape and which were recovered at a size site called Aramis, in •little difference in size between males Ethiopia, in late 1992 and females •Human like: teeth, thin enamel, and forearm bones •fundamental arboreal adaptations • Classic Prehumans • 4 million years ago- the climate seems to change. It became dryer like an increase in the same change, having happened around 10 million years ago. • The landscape opened. The covered part, which still existed, is diminishing. Based on fossils of grass eating species of other orders and families (animals); change in plant type to grasses • Genus Australopithecus (anamensis, bahrelghazi, afarensis, prometheus) and Kenyanthropus playtops • Meat eaters, walked and ran better due to skeletal changes, more aggressive • Au. Anamensis skeleton showed exclusive bipedalism • Body size is increasing, sexual diamorphism is appearing • Teeth show diversification of diet (omnivorous); endocranial capacity was increasing (300 to 350 cc) Australopithecus afarensis • Eastern Africa (Ethiopia, Kenya, Tanzania); 4-3 My • 400-500 cc • Adaptations for living both in the trees and on the ground helped them survive for almost a million years as climate and environments changed • Chimpanzee like: Children grew Famous Fossil named Lucy rapidly and reached adulthood earlier than modern humans.

•Less time for parental guidance and socialization during childhood. Flat nose, a strongly projecting lower jaw, and braincase <500 cc- about 1/3 the size of a modern human brain), • Long, strong arms with curved fingers adapted for climbing trees. • Human like: Small canine teeth like all other early humans • Stood on two legs and regularly walked upright (shape of the pelvis and the lower limb) • Open environment • Fossil footprints: 3.6 My at Latoli (Tanzania)- 3 individuals on wet volcanic ash Australopithecus anamensis • ‘anam’ means ‘lake’ in the Turkana • 4-2 My • stable hind limb (knee joint) and a quite instable forelimb (elbow joint), • Exclusive bipedality • protruding face and a long and narrow braincase Paranthropus – A Genus of Large toothed Hominins • para’ meaning ‘beside’ or ‘near’ and ‘anthropus’ meaning ‘man’. • 2 and 1.5 Ma. • Massive faces and lower jaws; • The brain, face and chewing teeth are larger than those of A. africanus, yet the incisor teeth are smaller. • Earlier and more primitive Paranthropus aethiopicus. • A smaller brain, around 400–450 cc, a more ape-like face and larger anterior (i.e. incisor and canine) teeth than does the later species, which is called Paranthropus boisei. The relationship between Ar. ramidus and A. anamensis

• Three hypothesis: 1. Either all hominins between 4.4 Ma and close to 3Ma consist of an evolving single species, or there are three separate species (Ar. ramidus, A. anamensis, A. afarensis) whose phylogenetic relations are imprecise 2. A. anamensis phyletically from Ar. ramidus within a 200,000- year interval; 3. A. anamensis from an ancestor (presumably Ardipithecus or some close relative) even deeper in the Pliocene or late Miocene. Under the latter hypothesis, Ar. ramidus would represent a relict species in an ecological refugium. Appearance of Genus

• About 2 mya, fossils begin to appear from our own genus, Homo • change in the brain • Form of the skull changed. • The upper cranium of the skull expanded and assumed a more rounded shape, permitting brain size to increase from about 450 cc to between 800 and 1200 cc. • the protruding jaw receded a bit, teeth became smaller, and height increased. • Two behavioral phenomena are striking: Tool use and Migration • Fossils have been found in China, Southeast Asia, and southern Eurasia Broadly four commonly used criteria for allocating individual fossils to species of Homo (not that these are free of debate) 1) the ability to manufacture stone tools, 2) the related possession of modern human-like precision grip (Leakey et al. 1964; Tobias 1991), and 3) the language competence (Tobias 1991). (difficult to establish from fossil record) 4) the absolute brain size Story of distinction between Australopiths and Homo • Small brain vs. large brain of homo • But in 1964 smaller brains were discovered for Homo by Leakey et al. • That led to formation of different species classification of H.habilis (with new small brain specimens) (500-700 cc) • H. rudolfensis (for large brain specimens) (700-800 cc) • Evidence from fossils are often not well preserved to define evolutionary relationships • H. Habilis is reduced in width and the opening of the nose is more sharply defined than H. rudolfensis • This suggests that the posture and locomotion of H. habilis sensu stricto were much like that of Australopithecus and Paranthropus. Neanderthals (H.heidelbergensis) • Disagreement whether they were different species or not? • Arguments for— – Morphological justification – Mitochondrial DNA • Recent contrary evidence— – Nuclear genome (complete set of DNA) (2010) that population outside Africa retain 4% of the DNA • Biological species concept would put them with H.sapiens – Complex biology and evolution—e.g. wolves and dogs • So, most likely— • Neanderthals were different species and also part of our direct lineage – Causes of speciation: reproductive isolation, behaviour/ structural obstructions; gametic incompatibility etc. • The characteristics: • a large, globular- shaped cranium, jaws and teeth that are set well forward in the face, and particularly robust limb bones with large joint surfaces. • The earliest Neanderthals come from Spain and France. Dated to 300–400 ka, with some evidence being as old as 700– confined to Western Europe, the 800 ka. The youngest Near East and adjacent parts of Neanderthal fossils are Asia. dated to around 30 ka. Homo Moves Out of Africa • H. ergaster-like hominin • may be in the order of 1.8 Ma old • Archaeological evidence suggests that hominins had occupied Europe and the Near East by around less than 1 Ma and perhaps even earlier, • At the southern African site of Swartkrans there is evidence of an ‘early Homo’-like hominin around 1.5 Ma. • Remains of H. erectus persist in the Far East, at the Chinese site of Zhoukoudian, near to Beijing, as late as 200 ka before the present. Peopling the Planet

• Modern humans were dispersed across the Old World by 25 to 35 ka. • As early as 150 ka and certainly by 59–60 ka, they had also managed to cross the water barriers between the Asian mainland and Australasia. • Earliest archaeological evidence of modern human occupation of Siberia dates from 20–30 ka • Hunting 40 ka or earlier • Agriculture 12 ka

• https://www.youtube.com/watch?v=vJybfmbrOCE Role of Theory Environmental pressures: •The savannah hypothesis •The variability selection hypothesis: ...faced with extremes, a species has three options, (Potts, 1996): Die out, move to a suitable range, or become more adaptable. •https://www.climate.gov/news-features/climate-and/climate-and- human-evolution

Pulsed nature of hominin speciation and migration events???

The turnover pulse hypothesis •A region specific hypothesis, the pulsed climate variability hypothesis