Human Evolution and Bipedalism Quiz

Final Exam Review - ANTH102, Fall 2024

• Exam date: December 19, 2024
• Time: 8:30 AM - 10:30 AM
• Note: Exam time is different from usual class time.
• Study concepts, taxa, and sites on the review sheet.
• Good luck!

Geological Studies and Past Life

• Geological studies provide a record of past life, allowing reconstruction and interpretation of evolutionary changes.
• Without a chronological sequence, the fossil record would be scientifically useless.
• Geological time provides a detailed record of major changes and events in evolution.

Geologic Time Scale

• The provided image shows a detailed geologic timescale.
• Note the different periods and their durations (in millions of years).
• Key events such as extinctions are marked.

Dating Methods

• Relative dating methods (e.g., stratigraphic correlation, chemical, biostratigraphic, cultural dating) help understand the sequence of past events.
• Absolute dating methods (e.g., tree rings, radiometric dating - K/Ar) provide specific time frames.
• Dating methods help answer questions about when past organisms were alive and understand past environments.

Radiometric Dating

• Isotopes are different forms of the same chemical element.
• Some elements are unstable and change from one isotope to another (radioactive decay).
• The decay rate is relatively constant.
• By calculating the decay rate and measuring different isotopes, rock/mineral age can be determined.
• The Potassium-Argon (K-Ar) dating is a specific method used for dating volcanic rocks effectively because volcanic rock is prevalent across the world.

Law of Superposition

• The lower layers of rock (strata) are older than the upper layers.
• The oldest rock layers are at the bottom, and the youngest at the top.

Strata and Fossils

• Strata (layers of rock) represent periods of deposition.
• Each stratum contains fossils representing a unique collection of extinct species.
• The earliest life forms are found in the oldest rocks; younger rocks contain newer life forms.

Possible Reconstructions

• Geological studies enable reconstruction of past environments, extinct species, major evolutionary timelines, speed of evolution, and the environmental pressures that affected past species.

Primate Fossils in the Fayum, Egypt

• The Fayum Depression in Egypt has yielded many early primate fossils (Oligocene epoch, ~34 million years ago).
• Apidium is thought to be an ancestor of certain primates, based on its dental formula.
• Aegyptopithecus is considered a potential common ancestor of catarrhines (Old world monkeys and apes).

Features of Humans Linking Us to Other Life on Earth

• DNA and RNA are found in all living organisms, reflecting shared ancestry.
• Multicellularity of invertebrates in ancient oceans is a recognizable feature
• Tetrapod ancestry reflects descent from lobe-finned fish.

Mammal Evolution and Dinosaur Extinction

• The presence and later extinction of dinosaurs affected mammal evolution.
• The extinction cleared ecological niches, allowing for wider mammal radiation and diversification.
• Competition prior to extinction limited diversification; post-extinction, more open ecological niches created the opportunity for mammals to fill various roles.

Theories of Primate Evolution

• Arboreal hypothesis: Primate traits evolved as adaptations to arboreal (tree-dwelling) life (grasping hands, binocular vision). However, other arboreal animals lack these traits.
• Visual predation hypothesis: Primate traits are adaptations for preying on insects and small creatures, leading to need for increased dexterity and visual acuity. This does not explain many primate diets that are not insectivorous.
• Angiosperm radiation hypothesis: Primate traits evolved in response to the evolution of flowering plants (angiosperms), leading to increased fruit consumption.

Crania and Postcrania of Miocene Apes

• Miocene ape crania and postcrania (skeletons) exhibit characteristics similar to modern apes (e.g., larger brain sizes compared to Old World monkeys).
• However, the postcranial skeletons generally resembled that of monkeys (less specialized for arm/leg length proportions).
• Miocene apes show mixtures of ancestral and derived traits compared to modern apes.

Climatic Change During the Miocene

• Climatic change during the Miocene favored monkeys over apes (cooler, drier, and more seasonal environments).
• Monkeys were better adapted to the wider range of food sources in drier environments, which was less readily available to the apes.

Characteristics Defining Hominins

• Bipedalism (habitual walking on two legs)
• Canine reduction

Skeletal Features Indicative of Bipedalism and Climbing

• Bipedalism: Foramen magnum positioned underneath the skull; S-shaped spine; short, broad pelvis; angled femur (valgus knee); enlarged femur/tibia joints for weight transfer; non-opposable big toe; arches in the foot.
• Climbing: Long arms; curved fingers/toes; a more arboreal-like general body structure. (Note: Some hominins show a mixture of traits)

Habitat Change During the Pliocene

• The Pliocene (3-2 million years ago) experienced climatic cooling, leading to drier conditions and more seasonal environments.
• Forests thinned, leading to open grasslands and savannas.
• This environmental change affected human evolution and may have contributed to the emergence of early Homo species, as well as the disappearance of gracile australopithecines.

Robust vs. Gracile Australopithecines

• Robust australopithecines (Paranthropus) had traits for heavy chewing (larger jaws, teeth, sagittal crests).
• Graciles (Australopithecus) had smaller chewing adaptations.

Dental Trends in the Genus Homo

• Early Homo had smaller cheek teeth and larger incisors than Paranthropus.
• A trend of reduced chewing complex occurred.

Explanations for Bipedalism

• Handy: Bipedalism frees hands for activities such as transporting food and utilizing tools.
• Cool: Bipedalism reduces body surface area exposed to the sun (better heat dissipation in hot environments)
• Efficient: Bipedalism is energetically more efficient than knuckle-walking.

Homo erectus Timeline

• Homo erectus emerged in Africa ~1.9 million years ago.
• It dispersed out of Africa ~1.8 million years ago.
• Homo erectus lasted longer in Asia (e.g. China).

Homo erectus Mating System

• High levels of sexual dimorphism in Homo erectus indicate a polygamous mating system.
• Competition among males for females was likely important.

Anatomically Modern Humans (Homo sapiens)

• Anatomical characteristics distinguishing Homo sapiens include a larger brain size, high and short brain case, and a short face tucked underneath the frontal region of the skull).
• Sophisticated tools (Aurignacian) and cultural developments may have given them an edge over other hominin species.

The Ultimate Success of Homo sapiens

• Cognitive changes (perception, understanding, and thinking) might be related to Homo sapiens' success.
• Sophisticated symbolic language use and cumulative cultural change may have occurred.

Mitochondrial and Nuclear DNA Analyses

• mtDNA and nDNA analyses indicate modern humans originated in Africa, with a high degree of genetic diversity.
• Analyses show that Neanderthals were not ancestral to modern humans but interbred with them.

Modern Human Origins Model

• The most plausible model for modern human origins includes replacement of other hominin species through gene flow (interbreeding)

Agricultural Evolution

• Population increased significantly.
• Competition for resources increased.
• Environmental degradation occurred.
• Cultural and technological changes had both positive and negative effects.

Infectious Diseases

• Infectious diseases existed long before agriculture and continue to impact current populations.
• Environmental conditions and human behaviors affect the spread of infectious diseases.