Early Humans: Meet the Ancestors

1. Early Humans: Meet the Ancestors 3. Bipedalism and Brain Growth; 3 to 10 mya

2. Objectives • Consider the evolution of humans from a common ancestor with other Great Apes • Main physical developments; bipedalism, changes to hands and feet and cranial capacity

3. Superfamily – Apes / Hominoids • Lesser Apes / Gibbons • Great Apes Orang-utan, Great Ape White-cheeked gibbon, Hylobates concolor

4. Homo (humans) Pan (chimps and bonobo) Gorilla Pongo (orang-utan) Silverback, Eastern Lowland Gorilla Genetic distance from humans 2.4 % Genetic distance from chimpanzees 2.4% Family – Great Apes / Hominids

5. Genera Pan – Bonobo and Chimpanzee Genera Homo – modern and extinct humans Chimp using a tool to dip for termites Genetic distance from humans 1.8 % Tribe - Hominin

6. African Great Apes Ancestor • Ouranopithecus macedoniensis • Nakalipithecus nakayamei jaw • Greece and Kenya, c 10mya • Diet of nuts and tubers

7. Pre-Knuckle walking split • Gorilla and other great apes “knuckle walk” • Ouranopithecus and Nakalipithecus don’t exhibit this trait • Knuckle walking a late evolutionary development

8. Feet • Gorilla foot with separate grasping big toe. • Human foot fully adapted for upright walking.

9. Time Line • Ardipithecus ramidus • Australopithecus anamensis • Australopithecus afarensis • Australopithecus africanus • Australopithecus bahrelghazali • Australopithecus garhi • Paranthropus boisei • Paranthropus robustus • Paranthropus aethiopicus • Homo habilis • Homo erectus

10. Ardipithecus ramidus • Aramis, Ethiopia • 4.4 mya • Earliest bipedal hominin • Cranium 300 - 350 cm3

11. Characteristics • Female 50kg • Teeth lacked the specialization -generalized omnivore. • Retains gripping toe • Fingers quite curved • Facultative biped – walked on the ground but quadruped in the trees Finger Ardipithecus ramidus bones

12. Why Walk Upright? • To free hands for tool use or carrying babies • But bipedalism develops prior to recognisable stone tools • Infants probably had strength to grip mothers’ hair

13. Aquatic ape - Wading in deep water • Idea originally proposed in 1942 • Popularised in 1960s by Elaine Morgan • Supported by other circumstantial evidence; webbed feet, nasal form, hairlessness

14. Objections • Most aquatic mammals are not hairless • Hair direction facilitate shedding rain as well as swimming • Most features supporting the theory don’t fossilise. • Fossil evidence for bipedalism not concentrated in areas bordering the ocean

15. Australopithecus Sites • Chad • Ethiopia • Kenya • Tanzania • South Africa

16. Savannah Adaptation • Energy efficiency locomotion • Stance improves visual range • More visually impressive when draw to full height • Cooler away from the ground • Reduced exposure to the sun

17. Laetoli, Tanzania • Bipedal footprints in volcanic ash, 3.5 mya • Arched foot • Lacks mobile big toe • Largest foot 21.5 by 10 cm, 47.5 cm pace, 1m/s = 3mph • All walking in same direction, possibly a family group

18. Australopithecus afarensis • Lucy, AL 288-1 • Ethiopia, 1974 • 40% complete • 3.2 mya

19. Arched Foot • Australopithecus afarensis • Hadar Ethiopia • 3mya • Permanently arched foot – comparable to modern humans

20. Knee joint • Austalopithicus africanus • Distal femur and proximal tibia joint. • Almost indistinguishable from modern humans.

21. Early Bipedalism • Relatively long arms and short legs. • Funnel shaped torso and rounded shoulders, lacks arm motion to aid running. • Feet and hands still relatively curved – retains tree climbing capability. • Early hominins’ inner ear more ape-like than human; anterior and posterior canals smaller and lateral larger than in modern humans – less well adapted to an upright posture.

22. Cost of Bipedalism • Changes to both feet and pelvis. • Aperture of pelvic girdle restricted with implications for child birth.

23. Australopithecus afarensis skull • Small cranium 405cm3 • Large brow ridges • Prominent lower face • No chin • Head is much closer to that of a chimp than modern human

24. Robust lineages • Paranthropus boisei – massive jaw and cheek bones. • Cranium 530cm3 • Male 49kg, 1.4m • Female 34kg, 1.2m • Larger brain but more musculature to control

25. Gracile Lineages • Australopithecus africanus • More human-likejaw and face • Cranium 510cm3 • Males 41kg, 1.4m tall • Females 30kg, 1.1m tall

26. Australopithecus garhi • 2.6 mya • Ethiopia Surprise in local Afar language • A gracile austalopithecine species • Cranial capacity 450 cm3 • Associated stone tools • Likely Homo ancestor

27. Australopithecines Diet • Dentition of robust species suggests more grinding than modern apes. • Microwear on teeth of gracile species comparable to chimps and orang-utan - suggests fruit important • Strontium – calcium ratio suggests some meat, again similar to chimps.

28. The Gut and Diet Orang-utans and chimps • small intestine 23-28% of total gut volume • colon 52-54% • Humans • small intestine 56-67% of total gut volume. • colon is 17-23%

29. Implications of High Quality of Diet • Smaller gut relative to body size. • Blood supply and energy diverted to brain development. • High quality food – small amount of time feeding – more time for social interaction

30. “Taung Child”, South Africa • Australapithecus africanus • Originally thought to be approx 7 years old • Now thought to be approx 3 years old • Ape-like rather than human rate of development

31. Sexual Dimorphism • Australopithecus africanus has lower sexual dimorphism – more like H. Sapiens

32. Summary of Pre-Homo development • Early bipedal development • Brain sizes comparable to contemporary non-human apes • Simple tools likely, but undetectable archaeologically before Australopithecus garhi • Species restricted to environmental niches • Childhood development ape-like, rather than delayed maturity of humans.