Week 12 Chimpanzees Dating things Intro to Human Origins Chimpanzees (Pan troglodytes) Chimpanzees Chimpanzees are perhaps the best known of all nonhuman primates. Most of us experience captive or trained chimpanzee behavior and consider it as being just like human. There is a difference between trained behavior and conscience choicedriven behavior 1
Chimpanzees are found in Africa in rainforests or in mixed forest-savanna environments. Like gorillas, they are knuckle-walkers with longer arms than legs, but they are more agile than gorillas. They are both terrestrial and arboreal. Chimpanzees Their diet consists of fruit, leaves, seeds, nuts, insects, and meat (small animals like monkeys). Chimpanzees live in large communities of 50 or more individuals. Their social structure constantly changes. They recognize and interact with others in thee group. The most important social behaviors revolve around mother and infant. Adult males are generally dominant. Fission-fusion arrangement Chimpanzees Fission-fusion society Multiple females and males live together in one group When resources are abundant, group stays together When resources are scarce, parties divided by sex Males create territories based on kinship More complex inter-sex relationships Teasing, Laughter, Embraces, Display 2
Bonobos (Pan paniscus) Bonobos are the least well known of the African apes. They are closely related to the chimpanzee, and commonly considered a separate species of chimpanzee known as pygmy chimpanzee. They are unique to a restricted rainforest region of Zaire, central Africa. Bonobos They eat a leaf and plant diet. Bonobos are distinguished from chimpanzees by their relatively longer legs, narrower chest, and higher center of gravity. Their forehead and face are also shaped differently. They can walk upright more easily than other apes. Bonobos It has been suggested that the first hominoids may have been quite similar in many ways. 3
Bonobos live in large multimale / multifemale groups like chimpanzees Strongest social bonds exist between adult females. Bonobos are known to practice polyandry Females withhold sex from males in return for less aggressive behavior Bonobos Dating the Past Our past can be revealed from clues accumulated over time. The fossil record provides us with bits and pieces of a small proportion of living organisms that have lied and died in the past. In order to use this information, we need to be able to determine time Dating Terminology Relative Dating Placing events in chronological order but without assigning numerical values. Example: Julius Caesar died before today s class. This was the only way anthropologists measured time in prehistory until the 20 th century. 4
Dating Terminology Absolute Dating Giving a calendar date to an event or events Example: Julius Caesar died on March 15, 44 B.C. Today s class occurred on A.D. June 24, 2011. Calendar dates use: BC/AD BCE before common era BP (bp) before present (1950) Flourine Dating 5
Relative Dating Methods Fluorine Dating measures the accumulation of fluorine levels in bone. The greater the amount of fluorine in bones from the same area, the older they are Pildown Man Human skull Orangutan jaw Relative Dating Methods Stratigraphy makes use of the geological process of superposition, the cumulative buildup over time of the earth s surface. 6
Absolute Dating " The Target Event is the event in which we are interested. " " E.g. when did these two hominids sit down to eat their dinner?" " The Dated Event is the event that a technique actually provides a date for." " E.g. when did the dirt surrounding their bodies fuse into rock? " 7
Target event vs. Dated event " " There can be (and often is) an unknown and significant time-span between these two events. " Hominids eat dinner Hominids die Bodies covered by landslide Dirt fossilizes Absolute Dating Use constant physical and chemical processes to determine exact dates, subject to statistical variation. Many techniques are useful for archaeology by not paleoanthropology Carbon-14 dating is only useful for sites as old as 50,000 years. Dendrochronology goes back 7,000 years But there are ways! Potassium -39 Protons (always 19) Neutrons (usually 20) Electrons 99.9% of all Potassium 8
Potassium -40 Protons (always 19) Neutrons (21) Electrons <.1% of all Potassium Electron capture In order stabilize itself, an unstable isotope may break a neutron and emit an electron (beta decay) This is what a Geiger counter measures Alternatively, it may combine an electron and a proton to form a new neutron Argon-40 Protons (always 18) Neutrons (22) Electrons 9
K/Ar Dating We can use the decay of 40 K to 40 Ar to date the age of rocks Potassium is a common component in felsic rocks (granite) Argon is stable and insoluble, so it will stay in the rocks until measured The amount of Ar in a sample can tell us how old the rock is Half life of 40 K Half-life 1,248,000,000 years 2 Half-lives 2,496,000 years 40 K decay 1.2 2.4 4.8 Billions of years 10
Fission Track Dating Based on the idea that as (other) radioactive isotopes go through beta decay (emitting electrons) These free electrons leave damage marks, or tracks, in crystals of rocks Electron Spin Resonance Alternatively, those track-causing electrons can become trapped in the lattice of crystals and affect the magnetic field By measuring changes in the magnetic field, we can determine how much time has transpired since mineral formation Reconstructing the Past Interpreting Fossils Identifying Species mostly relies on an examination of the morphology or structure of skeletal remains to infer evolutionary relationships with other specimens. Taphonomy: The study of what happens to plants and animals after they die. Paleoecology: The study of ancient environments. One example is palynology, the study of fossil pollen. 11
Interpreting Behavior Paleoanthropology employs a number of different methods that allow inferences of behaviors to be made. Stable Isotope Analysis is used on fossil remains to make inferences about diet. Experimental Archaeology involves learning how to make and use tools in the present in order to shed some light on tool making and tool use in the ancient past. Nonhuman Primate Models for Behavior provides insights into behavior during human evolution using comparative data from studies on nonhuman primates. How old are human beings? This can be answered in different ways: Roughly 200,000 years for those more or less anatomically the same as living human beings. All large-brained humans, several hundred thousand years. All members of the genus Homo, more than 2 million years. All bipedal hominids, 6 million years. 12
Humans and Apes The hominid line split from the African apes about 6-7 mya. They were bipedal and walked on the ground, but also climbed in trees. By 3 mya, two distinct lines of hominid had evolved. One line led to several species known as robusts. The other line began to rely more and more on learned behavior. Fossil Evidence of Early Hominid Evolution Evidence of fossil remains resembles a bush with many branches rather than a family tree. All species are classified as hominids because they show direct or indirect evidence of being bipedal. 13
Most early hominid species have been found at sites in South Africa and East Africa. Great Rift Valley Slide 41 Great Rift Valley 14
Evolutionary Stages Stage 1: lived 6+ mya to 4.4 mya. Evidence is fragmentary, but indicates bipedalism. Evolutionary Stages Stage 2: Australopithecines or primitive hominids and lived between 4.3 to roughly 2 mya. They were small-brained bipeds with primitive ape characteristics. Is highly diverse and represents a major split Evolutionary Stages Stage 3: Development of the genus Homo. Appearance of modern characteristics. 15
Genus Homo Australopithecine s Early hominids 16