Skeletons Reveal Human and Chimpanzee Evolution 1. What is a phylogenetic tree used to illustrate? It illustrates how species are related through evolution. 2. Based on genetic evidence, humans are most closely related to which two species? Chimpanzees and bonobos. 3. Are humans more closely related to gorillas or orangutans? State the evidence. Our genes (and our genome as a whole) are more similar to those of gorillas, indicating that we are more closely related to gorillas. 4. Charles Darwin proposed that modern humans directly descended from chimpanzees. Support or refute this statement with evidence from the video clip. Darwin did NOT think that humans descended from chimpanzees. His notes from 1837 suggested that modern species had common ancestors, not that some modern species had descended from others. More formally, his 1871 book The Descent of Man said, “We must not fall into the error of supposing that the early progenitor of the whole Simian stock, including man, was identical with, or even closely resembled, any existing ape or monkey.” 5. What is a hominid (or hominin)? A human – any species on the human side of the “last fork” of the primate family tree, representing the divergence of animals who would become modern chimpanzees and humans. 6. Australopithecus is an early hominid that is now extinct. Why does Dr. White contend that Australopithecus is not completely gone? Dr. White said, “Its gene are present, in altered form, in you and me.” In other words, we evolved from this ancestor and thus share some of its genetic material. 7. Identify at least TWO sources of data scientists can compare to determine the evolutionary relationships between two or more species? DNA sequences; anatomy and physiology 8. Bones are one anatomical feature that can provide a wealth of information. List SEVEN things scientists can learn about an organism by examining its bones. Its overall size and shape; its age; the size of its jaw muscles (from ridges on the skull); whether it was a predator or prey (from eye position); its diet and social behavior (from its teeth); its reproductive physiology (from its pelvis); and whether it walked on 2 legs or 4 legs (from its spine and pelvis). 9. Once the finger bones of Ardi were discovered, why does the crew begin to excavate and sieve the surrounding area? To try to find more bones! 10. What is the point of marking the excavation site with small yellow flags? To indicate where each bone was found. 11. Why did the excavation site for Ardi need to remain wet? To avoid expansion and contraction of the clay (from alternate wet and dry periods), which could crush the fossils it contains. 12. List the key features of each structure in the table below. Anatomical Structure Chimpanzee Ardipithecus Blunter, small canines; less of a difference Large, sharp canines, Teeth between males and especially in males females Human-like (shallower, Ilium Long and flat somewhat rounded) Pelvis Ischium Long Similar to chimpanzee Divergent toe, flexible Divergent toe but rigid Feet foot for grasping foot structure Humans Similar to Ardi Shallow, rounded Shorter No divergent toe, rigid food structure 13. State which conclusions can be drawn from each set of information. a. Conclusions from teeth comparisons … Ardi males may have been less “violently competitive” than male chimpanzees. b. Conclusions from pelvis comparisons … Ardi walked bipedally but also may have climbed trees. c. Conclusions from feet comparisons … Ardi walked bipedally but also may have climbed trees. 14. Where does Ardi belong on the tree of life? State the evidence. Ardi is at least partly adapted for bipedalism (shallow rounded pelvis, rigid foot structure). Since bipedalism is unique to humans, Ardi probably represents a species from the humans-only branch of the tree. 15. Based on your answer above, is Ardi the common ancestor to humans and chimps? State the evidence. No. Since Ardi shows traits that evolved only in humans, it is not likely to be an ancestor of chimpanzees. Also, it lived 4.4 million years ago, which is after the point at which human ancestors were thought to diverge from chimp ancestors.