Human Evolution GO BACK. WE MESSED UP EVERYTHING!

Human Evolution Humans are Primates Human Ancestry Hominins Misconceptions About Human Evolution

What are Primates?

Primate Characteristics Hands Dexterous—fine motor control Nails—not claws Sensitive Eyes in Front of Face Loose Shoulder Joint Parental Care Why? : grasp branches : binocular vision = good depth perception : swing from branches https://www.youtube.com/watch?v=eV-gOL4t9Vk : protect helpless infants Adaptations for arboreal existence

Human Evolution Humans are Primates Human Ancestry Hominins Misconceptions About Human Evolution

When did Humans and Chimps Diverge? Most recent common ancestor: 5-6 Mya

Where Did Humans Evolve? Location? Evidence? Fossils Genetic evidence Africa

Human Evolution Humans are Primates Human Ancestry Hominins Misconceptions About Human Evolution

What are Hominins? Hominins—group consisting of modern humans, extinct human species and all our immediate ancestors Species to know: Ardipithecus ramidus Australopithecus A. afarensis A. africanus Homo H. habilis H. erectus H. neanderthalensis H. sapiens

Hominin Evolutionary Tree Ardipethicus

Ardipithecus ramidus 4.4 Mya Small brain 300-350 cm3 Slightly smaller than chimp

Hominin Evolutionary Tree Australopithecus

Australopithecus Arose 4.1 Mya 2 species to know What do you notice? Australopithecus afarensis (“Lucy”) Australopithecus africanus What do you notice? Small brain 400-500 cm3 Slightly larger than chimp Short: 1.1-1.5 m Bipedal: walk on 2 legs How do we know Australopithecus was bipedal? Lucy

Evidence of Bipedalism: Fossilized Footprints What happened? What do you see? 3.6 Mya in Laetoli, Tanzania, two Australopithicines walked through wet volcanic ash. When nearby volcano erupted again, layers of ash covered and preserved footprints. How is this evidence of bipedalism? Footprints made by 2 limbs, not 4

Evidence of Bipedalism: Foot What do you notice? Other primates Opposable big toe Big toe not in line with other toes Long toes Humans Non-opposable big toe Big toe in line with other toes Short toes Why the differences? How is this evidence of bipedalism?

Evidence of Bipedalism: Foot Other primates Live in trees Grasping foot for grabbing objects Humans Live on ground Platform foot for walking

Evidence of Bipedalism: Foot Australopithecus foot What do you notice? Looks like human foot Platform foot for walking on ground

Evidence of Bipedalism: Pelvis, Femur, Knee Bones What do you notice about legs? Chimpanzee Legs straight Human & Australopithecus Knock-kneed (thighs aim inward) Why are our legs like this? When we walk, briefly stand on 1 foot Knock-kneed keeps foot under center of gravity, aiding balance http://humanorigins.si.edu/huma n-characteristics/walking Australopithecus? Same as modern humans

Evidence of Bipedalism: Foramen Magnum Hole in skull through which spinal cord enters What do you notice? Chimpanzee at back of skull Human, Australopithecus at bottom of skull Why? How is this evidence of bipedalism?

Evidence of Bipedalism: Foramen Magnum Bottom of skull = upright posture (bipedal) Back of skull = quadrupedal What happens when human tries to be quadrupedal?

Advantages of Bipedalism Frees hands: carry things Gather food Parental care Elevates eyes See predators & prey better

Hominin Evolutionary Tree Homo

Homo Arose 2.5 Mya 4 species to know What do you notice? Bigger brain Homo habilis: 1st tools Homo erectus: 1st to migrate out of Africa Homo neanderthalensis: sometimes classified as subspecies of modern humans Homo sapiens: last 100 ky What do you notice? Bigger brain 600-1200 cm3 Taller

Human Evolution Humans are Primates Human Ancestry Hominins Misconceptions About Human Evolution

Misconceptions About Human Evolution Humans evolved from chimps If humans evolved from chimps, why are chimps still here? Human evolutionary tree is a ladder Upright posture and big brains evolved simultaneously

Humans evolved from chimps; What’s wrong with this idea? Humans did not evolve from chimps; rather, they share a common ancestor

If humans evolved from chimps, why are chimps still here? A new species can arise even while the parent species persists This question assumes that we are somehow “improved” over chimps, so they shouldn’t be here anymore; this is a misconception: each species is well adapted for its lifestyle

Human evolutionary tree is a ladder Each species improves upon and replaces the one before it What’s wrong with this idea?

What does the human evolutionary tree look like? Shrub with many branches At most times, many different hominin species lived simultaneously In many cases, new hominin species arose while the parent species persisted

Upright posture and big brains evolved simultaneously What’s wrong with this idea? Upright posture evolved 1st in Australopithecus Big brains evolved later in Homo

How Did We Get Our Big Brains? How has hominin brain size changed over time?

A Clue in Growth & Development What do you notice? Fetus skulls Human and chimp look similar Start large brain case & small jaw Brain case : jaw proportion similar Adult skulls Skulls look different Chimp has smaller brain case, larger jaw How can this help explain big brains in humans?

Large Brains Explained Grid on fetal skulls allows us to see relative growth of different parts of skull What do you notice? In both, jaw grows faster than brain case Adolescent chimp similar proportions to adult human Chimp continues to develop So, to get a bigger brain … Slow down the developmental process so human skull can grow over a longer time … then it and the brain will get bigger