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Unformatted text preview: Human Evolution This is a story of how science works to discover the path of human evolution: the questions scientists ask, the guesses they make, the data they gather, and the conclusions they draw. It is a story of strong emotions and bitter rivalries. When Darwin wrote the Origin of Species, he had only one sentence about the topic merely saying, "Light will be thrown on the origin of man and his history". In 1859, there was not a single "human" fossil known and everything was speculation. Today, we have thousands of hominid fossils and thousands of books and papers on the subject. Still we do not have enough. Though we now know many of the steps along the journey, we are woefully ignorant of the forces that molded our evolution, how much of it was due to natural selection, adaptations to particular environments; or sexual selection, traits that females or males chose when selecting their mates; or genetic drift; traits that occurred by chance mutation in the small human populations. The search goes on. Here then, is one story in the long journey to find our ancestors. December 17, 1992
When graduate student Gen Suwa saw a glint among the pebbles in the desert of Ethiopia, he knew immediately it was a "human" molar. Suwa called the team and on hands and knees they scoured the rocks looking for bone fragments. There ,near the village of Aramis, they knew they had something special , a hominin , older than Lucy--a once in a lifetime discovery. Tim White's team had done it again. Months and years were to pass as more pieces were found and pieced together-- pelvis, leg, ankle, foot, hand and jaw-- --the rarest of finds, a partial skeleton of a new "human" fossil. It was a female and they nicknamed it "Ardi," short for Ardipithecus ramidus ; not only a new species, but a new genus! The White team eventually found over 100 specimens of the new species. Anthropologist Owen Lovejoy of Kent University said, "This team seems to suck fossils out of the earth." White and others spent years removing clay from the bones with brushes, syringes, and dental tools. Suwa and Lovejoy made virtual reconstructions of the crushed skull and pelvis, scanning them with micro-computer tomography. Nine years later ,having mastered the necessary technology , Suwa had reassembled the fragments into a virtual skull. By March of 2009, and the 10th reconstruction, he was satisfied. In Ohio, Lovejoy was finally satisfied that his 14th version of the pelvis was accurate. In October, 2009, they published their results in Science magazine, 20 years after the first discovery. The Authors So where does Ardi fit in the scheme of human evolution? The fossils were found in a layer of soil sandwiched between two volcanic layers that are dated radiometrically as 4.4 million years old. So this puts it "This is not an ordinary fossil. It's not a chimp. It's not a human. It shows us what we used to be," said Tim White, co-director of the project, a paleontologist at the University of California at Berkeley. But just what did we used to be? Human Evolution
What do we know about the phylogeny of humans? Put the following animals in their correct position: chimpanzee, lemur, human, gorilla, orangutan, monkey Which animal belongs in position "C"? chimpanzee, lemur, human, gorilla, orangutan, monkey Which animal belongs in position "C"?
1) 2) 3) 4) 5) 6) chimpanzee lemur human gorilla orangutan monkey 30 0%
6 Which 2 animals are out of place in this cladogram?
Monkey Lemur Orangutan Gorilla Human Chimpanzee Which 2 animals are out of place in this cladogram?
Monkey A) B) C) D) E) Lemur & Monkey Orangutan & Gorilla Human & Chimpanzee Orangutan & Monkey Gorilla & Chimpanzee Lemur Orangutan Gorilla Human Chimpanzee Which 2 animals are out of place in cladogram?
A) B) C) D) E) Lemur & Monkey Orangutan & Gorilla Human & Chimpanzee Orangutan & Monkey Gorilla & Chimpanzee 0% 0% 0% 0% 0% 30 Lemur Monkey Orangutan Gorilla Human Chimpanzee Primate Traits
1) 2) 3) 4) 5) 6) 7) 8) 9) 10) Nails instead of claws; digits with dermal pads Prehensile (grasping) hands & feet Five fingers & toes Tendency toward complete bony eye orbits Forward placement of eyes Opposable toe & thumb Enlarged cerebral hemispheres One pair of thoracic mammary glands Well developed clavicles (collarbones) Reduced olfactory sense & increased vision Key Steps in Primate Evolution
1) Development of Opposable Thumb & Grasping Hand 2) Posture/Bipedalism 4 legged 2 legged Increases sight range Frees hands for manipulation &carrying Loss of opposable toe Loss of tail Change in pelvic girdle Shift in foramen magnum Loss of opposable toe Shift for more stability Dog Shift Chimp in foramen magnum
(opening for spinal chord) Quadrupeds have it in the back of the skull. Bipeds have it underneath. Human Is this a biped or quadruped or something in between? A) Biped B) Quadruped C) Not strictly either,but in between Eye socket 23
View from underneath skull 3) Skull shape changes Face shortens & Brain case enlarges Prosimians (e.g. lemurs) Simians
(e.g. monkeys) Shape of Jaw Changes 4) Brain Size Increases Primate Brains Human Chimpanzee Monkey 5) Increase in Body Size 6) Reproduction As body size increases Embryo & offspring development time Parental Care increases Transfer of Learning from parents 7) Social Behavior increases in complexity, with increased co-operation and communication Solitary Small family groups Tribes Nations How many human-like species were alive 1.7 million years ago? One B) Three C) Four D) Five E) None of the above
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How many human-like species were alive 1.7 million years ago? A) One B) Three C) Four D) Five E) None of the above How is Ardi related to the other Hominids? 1) It directly evolved into Homo. 2) No reason to believe it is related to any other species. 3) It probably gave rise to Australopithicus 4) It evolved from Orrorin It directly evolved into Homo. 2) No reason to believe it is related to any other species. 3) It probably gave rise to Australopithicus 4) It evolved from Orrorin
1) How is Ardi related to the other Hominins? It directly evolved into 30
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1 2 3 4 5 6 One common scheme What makes us human?
A) B) C) D) E) Primate hand Upright posture/bipedalism Large complex brain Tool use Language 0% And when did these evolve? 0% 0% 0% 30 0% Here is a reconstruction of Ardi For comparison look at these Was Ardi bipedal?
1) Yes, she was clearly bipedal 2) Sometimes she was and sometimes not. 3) No, she wasn't; just because an artist drew her this way, doesn't mean she was bipedal. 30
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3 Ardi's hands Look at her hands. What does their structure suggest? 1) Yes 2) No 3) You can't tell from this picture 0 %
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3 ) Did Ardi knuckle-walk?
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3) Ardi's feet Look at her feet. What does their structure suggest? Is there an opposable toe? 1) 2) 3) Yes No Can't tell from the picture 0 %
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3 ) 30 Look at Ardi's pelvic girdle Chimpanzee Modern Human Ardi Was Ardi bipedal? Which picture best represents Ardi? A) B) C) D) E) F) 30
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1 2 3 4 5 6 "These are very odd creatures," says paleoanthropologist Allan Walker of Pennsylvania State University. Tim White says, "If you want to find something that moved like these things, you'd have to go the bar in Star Wars." What did Ardi eat? H. sapiens Ardi Chimp Ardi's teeth are rather general and she was probably ate a variety of food. Notice that her canines are less pronounced than chimps which use them for fighting. This has been interpreted to mean that she was less aggressive. Where would you place Ardi in this sequence? A)
B0 C) D) E) F_ G) H) I) J) 45 Here's Ardi
0 % 0 % 0 % 0 % 0 % 0 % 0 % 0 % 0 % 0 % 1 2 3 4 5 6 7 8 9 1 0 (A) Pan troglodytes, chimpanzee, modern (B) Australopithecus africanus, STS 5, 2.6 My (C) Australopithecus africanus, STS 71, 2.5 My (D) Homo habilis, KNM-ER 1813, 1.9 My (E) Homo habilis, OH24, 1.8 My (F) Homo rudolfensis, KNM-ER 1470, 1.8 My (G) Homo erectus, Dmanisi cranium D2700 , 1.75 My (H) Homo ergaster (early H. erectus), KNM-ER 3733, 1.75 My (I) Homo heidelbergensis, "Rhodesia man," 300,000 - 125,000 y (J) Homo sapiens neanderthalensis, La Ferrassie 1, 70,000 y (K) Homo sapiens neanderthalensis, La Chappelle-aux-Saints, 60,000 y (L) Homo sapiens neanderthalensis, Le Moustier, 45,000 y (M) Homo sapiens sapiens, Cro-Magnon I, 30,000 y (N) Homo sapiens sapiens, modern These are the bird species that were found in the same fossil deposits as Ardi. Where Did Ardi Live? 1) Desert 2) Aquatic 3) Prairie 4) Jungle 5) Woodland 45
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5 ) The anthropologists concluded that Ardi lived in a woodland, climbing hackberry, fig, & palm trees coexisting with monkeys, kudu antelopes, and peacocks. Doves and parrots flew overhead. "Multiple lines of evidence now suggest that they were beginning to leave the trees before they left the forest," said Stanley Ambrose of the University of Illinois. Timeline of Hominid Evolution 1) 80 kg 2) 60 kg 3) 50 kg 4) 40 kg 5) 30 kg 6) 20 kg 7) 10 kg Body weights of different hominids. Predict the body weight of Ardi assuming she fits into the overall trend. Remember she is dated at 4.4 million years ago. 30 4.0
0 % 1 ) 0 % 2 ) 0 % 3 ) 0 % 4 ) 0 % 5 ) 0 % 6 ) 0 % 7 ) Body weights of different hominids.
Predict the body weight of Ardi assuming she fit into the overall trend. Remember she is dated at 4.4 million years ago. 1)80 kg 2)60 kg 3)50 kg 4)40 kg 5)30 kg 6)20 kg 7)10 kg Experts' prediction 50kg x
4.0 Based in these data, what would you predict the brain size of Ardi to be given that she was dated at 4.4. million years? 1) 1500 cc
2) 1200 cc 3) 1000 cc 4) 750 cc 5) 500 cc 6) 350 cc 7) 200 cc 8) 100 cc
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8 ) 30 Brain size of Ardi?
Based in these data, what would you predict the brain size of Ardi to be given that she was dated at 4.4. million years? 1)1500 cc 2)1200 cc 3)1000 cc 4)750 cc 5)500 cc 6)350 cc 7)200 cc 8)100 cc Experts' prediction x
4.0 300-350 cc Primate Brains
Ardi had a brain the size of a chimpanzee Human Chimpanzee Monkey What is the driving force (natural selection) for an increase in brain size in primates and humans in particular? Increased complexity of social behavior and communication 2) Need for a better memory for long range hunting trips 3) Need for better temperature regulation control because of running down prey--the strategy of African hunters. 4) Increased use of tools and fire
4) Summary From the 11 papers in Science October 2, 2009 The skeleton nicknamed "Ardi" is from a female who lived in a woodland, stood about 120 cm. tall and weighed about 50 kg. She was thus about as big as a chimpanzee and had a brain size to match. She did not knuckle-walk or swing through the trees like living apes. Instead she walked upright, planting her feet flat on the ground, perhaps eating nuts, insects, ad small mammals in the woods.
(There is no evidence that she used fire or communicated any more effectively than chimpanzees.) Rather than humans evolving from an ancient chimp-like creature, the new find provides evidence that chimps and humans evolved from some long-ago common ancestor--but each evolved and changed separately along the way. "This is not that common ancestor, but it's the closest we have ever been able to come," said Tim White, director of the Human Evolution Research Center at the University of California, Berkeley.
Chimps Humans Common ancestor Ardi Now, it is December again and Tim White and his team are back in Ethiopia, picking among the stones and rocks. The team has made another discovery, a dozen pieces of a skull. It looks like Australopithecus . "It's a big boy, big for an australopithecine," says White. Maybe it is Australopith garhi. On the way back to camp, White stops to take a snapshot of the moon rising over Yardi Lake. The landscape has changed over time, but one thing is constant, White notes, "Hominids have been right here looking at the moon rising over the water for millions of years." ...
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This note was uploaded on 12/09/2009 for the course BIO 200 taught by Professor Herreid during the Spring '07 term at SUNY Buffalo.
- Spring '07