Humans as Bipedal Primates Flashcards
What does arboreal mean?
Acting/living in trees
What is the Broca’s region?
A region of the brain concerned with the production of speech, located in the cortex of the dominant frontal lobe
What is the brow ridge?
A bony ridge located above the eye sockets if all primates.
What is the cranium?
The part of the skull that encloses the brain
What is formen magnum?
The large opening at the base of the skull through which the spinal cord passes
What is the nuchal crest?
A bony ridge at back of the skull. It is where the neck muscles and ligaments are attached in order to support the head.
What is the mandible?
The lower jaw or jawbone
What is an obligate biped?
Adapted for walking only on two legs, with no ability to walk on four.
What is an opposable thumb?
A thumb that can be placed opposite the fingers of the same hand
What is a prognathic jaw?
A “forward jaw”. Describes the degree to which the maxilla and mandible (the muzzle) extend forward of the face.
What is a saggital crest?
A bony ridge on the top of the skull to which the jaw muscles are attached.
What a valgus angle?
The angle the femur makes relative to the knee. Close to 90 degrees in non-human apes, less in bipedal humans.
What is the wernicke’s area?
A region of the brain concerned with the comprehension of language, located in the cortex of the dominant temporal lobe.
What is a zygomatic arch?
The bony arch at the outer border of the eye socket, formed by the joining of the cheekbone and the zygomatic process of the temporal lobe.
What is bipedalism?
Having two feet and using two feet for locomotion.
What is obligate bipedalism?
Walking only on two legs with a reduced ability to walk on all four.
The main trait that defines the hominin lineage and separates us from the rest of the apes.
Why do humans have a barrel shaped ribcage?
Allows the arms to swing freely from side to side to assist with balance when walking upright.
How have human feet evolved?
Toes are straighter and shorter. The big toe (hallux) is larger and more robust, aligned with the other toes for propulsion. Well developed arches. Robust heel that can absorb forces encountered during heel strike.
What do chimpanzee feet look like?
Opposable hallux used for grasping branches. Foot lacks arches and the entire surface of the foot makes contact with flat ground.
Human Foramen Magnum and Nuchal Crest
Foramen Magnum is nearer the centre of the skull and opens directly downward.
Humans have a cranium that rests on top of the vertebral column so the position of the Foramen magnum helps to balance the mass of the head above the spine.
Humans don’t have a large nuchal crest at the back of the cranium like the apeas.
Ape Foramen Magnum
Foramen magnum lies towards the back of the skull.
Human spine
S shaped spine brings the body’s centre of gravity directly over the middle of the pelvis and allows rhe spine to flex and absorb forces during locomotion.
Chimpanzee spine
Bow shaped supports abdomen and helps to absorb forces generated by quadrupedal locomotion.
Human pelvis
Shorter, broader, bowl shaped. Supports the gut when upright.
Human femur
Valgus angle femur. Places feet directly below the centre of gravity as knee joints are closer to the mid-line than the hips.
Environmental changes that led to selection pressure for Bipedalism
Relied on forest for food, shelter from the sun and hide from predators.
Forests broke up with climate change and the climate became cooler and dryer, giving way to scattered woodland and savannah.
Advantages of Bipedalism (PEFT)
Predator avoidance: Stand up, look over tall grass, identify and avoid predators.
Energy efficiency: Biped walking uses less energy, longer journeys
Freeing the hands: Carry more food/weapons
Thermoregulation: Biped subject to less solar radiation while standing upright.
Bipedalism and the hand: Humans
Shorter, straighter fingers, not required for brachiation.
Opposable thumb, more muscular and mobile.
Wrist mobility, fully rotate hands and extend hands.
Human brain
Larger than chimpanzees, more complex brain, larger frontal lobe that allows us to have abstract and logical thought, imagination, complex language and artistic ability.
Cerebellum - refined fine motor skills and coordination, balancing, coordination
Larger frontal lobe - gives us the ability to have abstract and logical though, imagination, complex language and artistic ability
Brachiating
Locomotion accomplished by swinging by the arms from on hold to another
Habitual biped
Usually walks upright on two legs
Prehensile
An animal’s limb or tail that is capable of grasping
Sexually dimorphic
The differences in appearance between males and females of the same species
Terrestrial
Of or related to the ground or earth, particularly describing animals that live on the ground
Hominin
The group consisting of modern humans, extinct human species and all our immediate ancestors
Human feet
- Opposable hallux (big toe) provides efficient toe-initiated push-off for propulsion
- Longitudinal arches in foot means humans can push off ground with toes
- Robust heel - forces of heel strike are absorbed by heel bone and balance while standing
Human rib cage
Barrel shaped
Allows arms to be swung from side to side during bipedal locomotion
Chimpanzee rib cage
Cone shaped.
Contains relatively large gut, allows for wide range of arm motion for brachiation
How did the environment changing allow for bipedalism?
The mid-late miocene was a predominantly forested area. This meant that arboreal lifestyle to escape terrestrial predators, travel to food sources, nest and find shade was easy.
The climate became cooler, drier and water sources became limited. This resulted in grassland and open woodland.
This meant that bipeds had to range further to find food. They would have to carry objects and avoid predators. Being able to brachiate would become less important than being able to walk efficiently
