D.3.4 Describe the major anatomical features that define humans as primates. human gibbon gorilla Grasping pentadactyl limbs
Reduced snout leading to reduced olfaction vs. Squirrel Doggie Monkey Human
Generalised Dentition Human Baboon Gorilla Moo Cown
Others: Forelimbs able to twist Clavicle allows wide range of arm movement (re. the above two points: if you have a gentle and patient pet dog, give it a rub on the tummy and then move its forelegs, they really only move in one plane) Slower reproduction - long gestation - usually one offspring at a time Larger skull – relative to body size Large brain – more complex, more folds Better visual acuity – more of the photoreceptors have their own sensory neurons Social dependency
Human hands are adapted for grasping and fine manipulation. In contrast gorillas have short fingers for knuckle walking and gibbons have elongated fingers and reduced thumbs for brachiating.
D.3.5 Outline the trends illustrated by the fossils of Ardipithecus ramidus, Australopithecus including A. afarensis and A. africanus, and Homo including H. habilis, H. erectus, H. neanderthalensis and H. sapiens. knowledge of approximate dates & distribution of the named species is expected
HOMINOIDS Ardipithecus ramidus: about 4.4 m.y.a. ; Eastern Africa – One of the most primitive hominids Small cranial capacity (size = female chimp; 20% of modern human) – Facultative biped: walk on ground for short distance but can grasp trees using hallux (big toe) – Shares some aspects of its teeth with later hominids Reduced canines – Have recovered approximately 45% of skeleton
Australopithecus afarensis (Lucy): 3.6 to 2.9 m.y.a.; Southern & Eastern Africa – upright posture (bipedal) – evidence of coexistence with A. africanus for about 1 million yrs HOMINOIDS (cont.)
Australopithecus africanus: 3 to 2.4 m.y.a. – walked upright (bipedal) – humanlike teeth and hands – brain was about 1/3 size of modern humans – Fossils are sufficiently different than Lucy to be a different species Chimpanzee Australopithecus africanus Homo sapiens
hominids walked upright for two million years without a substantial increase in brain size this posture may have freed the hands for other things such as gathering food or caring for infants In arid environments, bipedal walking requires less energy than walking on all fours
Homo habilis: 2.4 to 1.6 m.y.a. Eastern & Southern Africa Earliest fossil in our own genus – enlargement of brain is evident in fossils dating back to about 2.4 m.y.a. (650 cc vs. 500 cc); shorter jaw Simple, sharp stone tools found with H. habilis coexisted with A. africanus for almost 1 million years (E. Africa) (A. africanus was an evolutionary dead end)
adult cranial capacity (range in cm 3 ) Chimpanzees Australopithecines early transitional humans modern humans
Homo erectus: 1.8 m.y.a. to 200,000 years ago migrated out of Africa – Found in former Soviet Republic of Georgia Increase in brain size Decrease in jaw size Vertical shortening of the face Reached modern human height
H. erectus found on other continents diet shifted to include a larger portion of meat intelligence allowed them to survive in colder climates (lived in huts or caves, built fire, wore clothing, designed more refined tools) *correlation between change in diet & increase in brain size
(Homo neanderthalis): 200,000 to 30,000 yrs ago -lived in Europe, Middle East, & Asia -Appear to have descended from H. heidelbergensis which originated in Africa 600,000 years ago & then spread to Europe & the Near East - large brains, made hunting tools of stone and wood - Did not contribute in a significant way to the gene pool of humans (extinct 30,000 years ago)
Homo sapiens: 195,000 years ago to present day Oldest known fossils of our own species have been found at two different sites in Ethiopia (195,000 & 160,000 years old) Lacked heavy brow ridges of H. erectus & neantherthalis More slender than other hominids Evidence of sophisticated thought: 77,000 year old art; 36,000 year old cave paintings Coexisted with Neanderthals
Cro-Magnon cave art, Upper Pleistocene.
On the next slide, look at the skulls and note the morphological differences between the different fossils and modern man.
Ardipithecus ramidus Australopithecus africanus Australopithecus afarensis Homo habilis Homo erectus Homo neanderthalensis Homo sapiens Skulls not to scale
1. Gorilla 2. Australopithecine 3. Homo erectus 4. Neanderthal (La-Chapelle-au-Seine) 5. Steinheim Skull 6. Modern human
From the previous two slides you can see these trends: enlargement of the brain case shortening of the face loss of brow ridges
Homo sapiens Pan troglodytes (chimpanzee)
The jaw has developed from a U into a V shape. Teeth have generally reduced in size. (Chimpanzee provided for comparison)
Also, there is a hole in the bottom of the skull where the spinal cord exits the brain (foramen magnum). The foramen magnum is further forward in modern humans. This distributes the weight of the head over the spine so that modern humans do not need huge necks muscles.
Skeleton, locomotion and posture- look for trends! Human knees aligned under the bodys center of gravity because femurs are angled inwards. Human legs straighten completely when walking. Human spine has additional curves to keep centers of mass of head and trunk aligned for bipedalism. Big toe not opposable in humans, which allows for an arched foot. Ratio legs:arms greater for humans than other apes Human pelvis broader
TOK Read the article on Wikipedia about Homo floresiensisHomo floresiensis Discovered in 2004 on the Indonesian island of Flores, it has stirred up controversy in the palaeoanthropological world. Is it a separate species or is it the remains of diseased Homo sapiens. You be the judge! Short PBS video
D.3.7 Discuss the incompleteness of the fossil record and the resulting uncertainties about human evolution. It isnt easy to create a collection of fossils that clearly show the change of species from one to another. Fossils rarely result when an animal dies for the following reasons: Decomposition is usually rapid; soft body parts are rarely fossilized. Scavengers usually break up skeletons and even chew up bones. The conditions have to be just right for fossilization to occur. Only a tiny, tiny, tiny fraction of all of the fossils in existence have been found.
Skulls and teeth are usually the parts of the ancestral hominids that survive to be fossilized and found Therefore there is a lot of conjecture as to where they all fit in the family tree. Hypotheses are often overturned by new discoveries that rewrite the relationships between the species.
The large gaps in the human evolution fossil record are consistent with punctuated equilibrium The following four slides show how the gaps are filled over time with new discoveries. The graphs plot cranial size against the age of the fossil.
Despite the fossil evidence we have so far, there are still large gaps in our knowledge. We have no fossil for the last common ancestor of humans and chimpanzees It is believed to have lived 6-8 million years ago Find out how this estimate was determined
D.3.8 Discuss the correlation between the change in diet and increase in brain size during hominid evolution. The benefits of a bigger brain include: More complex tools Mastery of fire Cooking Warmth Protection Greater behavioral flexibility (less reliance on instinct and better able to learn and pass on knowledge necessary to adapt to an environment)
The cost of having a big brain: Longer gestation period Years of development before young can look after themselves Much more brain development occurs post birth that for any other animal In summary: Big brains are energetically expensive. The mother must take in lots of energy not only during pregnancy, but for a significant time after due to nursing. Hominids needed to increase their energy uptake. Left: chimpanzee infant head size relative to pelvic opening; Right: human infant head size relative to pelvic opening
The solution to this energy crisis was to swap a diet of these:
For some chunks of this: The increase in brain size observed in hominid fossils has been closely correlated with an increased intake of meat. A bigger brain made hunting and killing easier.
D.3.9 Distinguish between genetic and cultural evolution. Biology H & IB Biology 1 has dealt with genetic evolution. In this context, it refers to the genetic changes that have occurred during the evolution of hominids. e.g. increased brain size, spine shape, position of knee, etc. Cultural evolution is the changing of ideas held and actions carried out by societies and the transmission of these ideas through social learning from one generation to the next. e.g. the use of fire, agriculture, tools, weapons, religion, beliefs
D.3.10 Discuss the relative importance of genetic and cultural evolution in the recent evolution of humans. TOK Read this article: Are We Still Evolving? What do you think of the arguments for and against this proposition?
However, we have not changed biologically in any significant way. We could take a baby from 80,000 years ago, raise it in a modern environment and it would be indistinguishable from other humans in terms of intelligence and social capabilities. The cultural evolution has spanned millions of years in three major stages: the nomadic (hunting), agricultural (settled), and industrial ages.
BBC Website Further information: Excellent site!