HUMAN EVOLUTION Option D.3 IB Biology Miss Werba

OPTION D - EVOLUTION D.1 ORIGIN OF LIFE ON EARTH D.2 SPECIES AND SPECIATION D.3 HUMAN EVOLUTION AHL D.4 THE HARDY–WEINBERG PRINCIPLE AHL D.5 PHYLOGENY AND SYSTEMATICS J WERBA – IB BIOLOGY 2

THINGS TO COVER Absolute dating using radioisotopes Major physical features that define humans as primates Trends in fossils of Australopithecus and Homo Coexistance of species of the family Hominidae Incompleteness of the fossil record Correlation between the change in diet & increased brain size in hominid evolution Difference between cultural & genetic evolution J WERBA – IB BIOLOGY 3

RADIOACTIVE DATING Command term = OUTLINE Fossils contain isotopes of elements that have accumulated in the living organisms. Isotope: an atom which has a different mass to the other atoms of the element, caused by a different number of neutrons within its nucleus. If the isotopes are unstable, they will break down over time, changing into other elements and emitting radiation. This is called radioactive decay. J WERBA – IB BIOLOGY 4

RADIOACTIVE DATING Command term = DEFINE Each radioactive isotope has a fixed half-life. Half-life: The time it takes for half of a radioactive isotope to decay. J WERBA – IB BIOLOGY 5

RADIOACTIVE DATING Command term = OUTLINE Radiocarbon dating: Carbon-14 (14C) is an isotope of carbon (12C) The two forms are maintained in constant proportions while an organism is alive. When an organism dies, the proportion of carbon-14 begins to decrease. The proportion of carbon-14 remaining can be used to identify the age of a sample. Carbon-14 has a half life of 5,730 years Carbon-14 is therefore only useful for dating fossils up to ~60,000 years of age. J WERBA – IB BIOLOGY 6

RADIOACTIVE DATING Command term = OUTLINE Potassium/Argon dating: Potassium-40 (40K) is an isotope of potassium (19K) Potassium-40 is released in lava from active volcanos As it decays, it transforms into argon-40 (a gas) Potassium-40 has a half life of 1,300 million years Potassium-40 is therefore useful for dating fossils over one million years of age. J WERBA – IB BIOLOGY 7

RADIOACTIVE DATING Command term = DEDUCE J WERBA – IB BIOLOGY 8

RADIOACTIVE DATING Command term = DEDUCE J WERBA – IB BIOLOGY 9

THE ORDER OF THE PRIMATES Command term = DESCRIBE There are several anatomical features that define humans as primates: Opposable thumbs / grasping pentadactyl limbs Forward facing eyes/binocular vision Large brains relative to body size Flexible shoulder joints (provide large range of movement) Finger pads / nails not claws Reduced snout leading to reduced olfaction J WERBA – IB BIOLOGY 10

THE ORDER OF THE PRIMATES Command term = DESCRIBE Skull adapted for upright posture rotating hand (pronation) Tailless primate Generalised dentition (different types of teeth) Slower reproduction Better visual acuity Social dependency Parental care J WERBA – IB BIOLOGY 11

HOMINID FOSSILS Command term = DESCRIBE The word hominid refers to members of the family of humans, Hominidae. This family consists of all species on our side of the last common ancestor of humans and living apes, including members of the Pongo (orang utans), Gorilla, Pan (chimpanzees) and Homo (humans) genera. Homo sapiens is the only human species still in existence. The fossil record is incomplete but there is enough to give a good outline of the evolutionary history of humans. J WERBA – IB BIOLOGY 12

HOMINID FOSSILS Command term = DESCRIBE You are expected to be able to describe the trends across the following species: Ardipithecus ramidus Australopithecus afarensis Australopithecus africanus Homo habilis Homo erectus Homo neanderthalensis Homo sapiens J WERBA – IB BIOLOGY 13

HOMINID EVOLUTION Command term = STATE At various stages in hominid evolution, several species may have coexisted. J WERBA – IB BIOLOGY 14

INCOMPLETENESS OF THE FOSSIL RECORD Command term = DESCRIBE Fossilization is a rare occurrence. Most components of dead organisms decompose relatively quickly following death. Fossilization tends to favour hard body parts. Exposed fossils are soon destroyed/weathered, reducing the chance of them being found; Fossilization favours species that lived for a long time. J WERBA – IB BIOLOGY 15

INCOMPLETENESS OF THE FOSSIL RECORD Command term = DESCRIBE Very few fossils have been found so picture is incomplete Individual fossils may not be representative of species (ARE YOU?!?!!) Very few complete skeletons have been discovered Relies on a relatively small amount of data to draw conclusions. New discoveries regularly come to light, leading scientists to re-interpret previous assumptions in the light of the new data. J WERBA – IB BIOLOGY 16

RELATIONSHIP BETWEEN DIET & BRAIN SIZE Command term = DISCUSS What are the benefits of a bigger brain? Higher order thinking – like planning, hunting, inventing More complex tools Mastery of fire – for cooking, warmth, protection Ability to learn and pass on knowledge to the next generation to improve survival chances J WERBA – IB BIOLOGY 17

RELATIONSHIP BETWEEN DIET & BRAIN SIZE Command term = DISCUSS What are the costs of a bigger brain? Longer gestation period Longer period of development until they are self- sufficient Large period of brain development post-birth Energetically expensive! J WERBA – IB BIOLOGY 18

RELATIONSHIP BETWEEN DIET & BRAIN SIZE Command term = DISCUSS Tool making first associated with H. habilis. This would have required a larger brain. Larger brain requires vast amounts of energy, creating a demand for changes in diet. Changing to a higher calorie diet may have allowed further increase in brain size. Animal tissues (meat) can provide the necessary structural lipid for human brain expansion. J WERBA – IB BIOLOGY 19

RELATIONSHIP BETWEEN DIET & BRAIN SIZE Command term = DISCUSS As brain size increased, language and cognitive abilities also developed. Larger brain also allowed for better hunting and gathering, increasing the calorie intake even further. Changes in the dental fossil record are indirect evidence for such a change in diet. The increase in brain size in hominid fossils has been closely correlated with an increased intake of meat. J WERBA – IB BIOLOGY 20

CULTURAL & GENETIC EVOLUTION Command term = DISTINGUISH Is controlled by genes. Limited by the genotypes of the populations. Controlled by natural selection and selective advantage. eg. increase in cranial capacity in hominids J WERBA – IB BIOLOGY 21

CULTURAL & GENETIC EVOLUTION Command term = DISTINGUISH Cultural evolution: Based on skills/info passed from one generation to another New skills/info can be transmitted between different groups It is learned/taught. It is language dependent. Only possible because of large brains of the Homo species allow for learning. Allows more rapid evolution. eg. tool making, religion, art J WERBA – IB BIOLOGY 22

RECENT HUMAN EVOLUTION Command term = DISCUSS Changes in genotype have lead to cultural evolution in humans by promoting intelligent behaviour. Larger brain sizes have promoted increased learning/thinking capacity. Prolonged gestations have promoted social interactions and family networks. Bipedalism has promoted extensive migration and improved socialisation. Shorter finger bones and reduced reliance on forelimbs for locomotion have promoted increased tool manipulation. J WERBA – IB BIOLOGY 23

RECENT HUMAN EVOLUTION Command term = DISCUSS Evolution of culture (eg. art, science, language) has been more rapid and recent than genetic evolution (which requires many generations). Further cultural evolution (through genetic engineering and reproductive technology) may hasten changes in our genetic evolution. Certain products of cultural evolution (eg. medicines) may reduce genetic evolution via natural selection. Other products of cultural evolution (eg. pollution) may increase genetic evolution (increased mutagenic rate). J WERBA – IB BIOLOGY 24

Sample questions a) Outline a method for dating fossils using 14C. [2] Q1 (5 min) a) Outline a method for dating fossils using 14C. [2] b) Outline the trends illustrated by the fossils of Ardipithecus and Australopithecus. [3] J WERBA – IB BIOLOGY 25

Sample questions Q2 (4 min) Outline, using named hominid fossil species, trends in hominid skull evolution. [3] J WERBA – IB BIOLOGY 26