Life science - Hominid studies (evolution)

Hominids

-Modern and extinct great apes and humans e.g. the living african apes:

bonobo

gorillas

chimpanzee

Humans

Hominins

Modern and extinct humans and other immediate ancestors:

-Australopithecus

-Homo Habilis

-Homo erectus

what idea do we use to trace human ancestry?

-Hominids (humans and apes) share a common ancestor

-This common ancestor will be used to trace evolution from that common ancestor to today's humans

Hominid vs. Hominin

-We're all hominids but not all hominids are hominins.

-Some species are closer to Hominids than they are to Hominins.

What evidence is used to find a common ancestor between hominids?

-Fossil record and genetic evidence

-The common ancestor should have traits common to both humans and great apes

What does Arboreal mean?

-tree-dwelling

-Being able to swing on trees

Characteristics of primates (Arboreal)

-Clavicle (collar bone)

-Most mammals have lost their collar bones, primates have not

-The clavicle helps to stabilise the shoulder, allowing to support its weight by hanging from its arms alone

Characteristics of primates (arms and legs)

-They have long and slender arms that rotate freely at the shoulders and hips

-This helps them move in trees

Characteristics of primates (Thumbs)

-Most primates have mobile opposable thumbs and separate fingers

-Only the Catarrhines and a few lemurs have dexterous hands allowing them to grab onto branches effectively

Characteristics shared by all primates (O.L.N)

-Opposable thumbs with power and grip precision

-Long arms (freely rotating)

-No tail

DOC . LEN . BFVP (Digits . Opposable thumbs . Complex behaviours . Long arms . Eyes . No tail . Brain . Face . Premolars)

Characteristics shared by all primates (COMPLEX BEHAVIOUR)

-Complex social behaviours such as having one one offspring at a time for extended care

Characteristics shared by all primates (PREMOLARS)

-Primates have low rounded premolars and molars while other mammals have high pointed ones, this difference makes it easier to identify fossilised primate teeth.

Characteristics shared by all primates (DIGITS)

-Digits with flat nails meaning no claws or hooves (allowing for more sensitive manipulation, allow for better grip and grab).

Characteristics shared by all primates (BRAIN)

-An enlarged and complex brain relative to body size (other species have smaller brains relative to body).

Characteristics shared by all primates (EYES)

-Forward facing eyes that give stereoscopic vision and 3D vision, eyes with rods/cones that help with seeing in the dark and colors.

What is stereoscopic vision?

depth perception that leads to 3D vision

Characteristics shared by all primates (FACE)

-A flattened face, reduced snout, reduced sense of smell (as we rely mainly on vision as opposed to smell for food)

Evidence for a common ancestor in living hominids

-Hominids have ape-like and human-like features

-However humans did not evolve from African apes only they only share a common ancestor

-The common ancestor split into two lineages one led to the ape and the other led to humans

-(separate evolution)

Anatomical similarities between African apes and Homo Sapiens

-Upright posture

-Lack external tail

-Have opposable thumbs and separate fingers (thumbs that stick out sideways and allow for precision grip).

- Have digits and toes with flat nails

-Forward facing eyes (visual field overlaps for stereoscopic vision. Cones to allow for color vision)

-Premolars and molars with low and rounded cusps (we do not have sharp teeth cause we eat cooked food)

-Sexually dimorphic (males and females have different traits at times e.g. muscle mass)

-Have large brains compared to body mass

Anatomical differences between Chimps and humans

-Volume of chimp brain case is less than that of a Human braincase (400cm^3 : 1300cm^3)

-Pronounced brow ridge is present in chimps but not in humans

-Sexual dimorphism of the canines is greater in chimps than in humans

-Arms and legs of chimps are longer than those of humans

-Vertebral column of chimps is bow shaped whereas in humans is s shaped

-Pelvis of chimps is long and narrow whereas the of humans is broad and bowl shaped

-Hand bones of chimps are robust but those of humans are not

-Big toe of chimps is opposable for grip and is not opposable in humans.

How many hominin fossils have been found worldwide?

About 7000

How are fossils often found and how are they fixed?

-They are not always found intact and are reconstructed from fragments. (Radiometric/radioactive dating)

What are the most common fossils found?

-Teeth, remains of femurs, upper cranial bones of skull, lower jaws, facial bones

What fossils are rare to find

-Hands, feet, pelvis, spine

How are skulls usually found

-They are never found intact and usually have to be reconstructed

Why is the study of fossilized bone important?

-Helps scientists to learn about the changed physical appearance of earlier hominins and how they changed over time

What can scientists find out about a fossil bone

-The markings left on the bone by muscle suggest size and shape of the bone and indicates how the hominins moved and held tools (angle of bone to see if bipedal or quadrapedal)

-Is the fossil record complete?

-It is incomplete but offers enough evidence to provide a good outline of the evolutionary history of homo sapiens

What are paleontologists and what key features of fossils do they study?

-Scientists that study fossils

-Bipedalism, skull (brain size), dentition, prognathism, palate shape, cranial/sagittal and brow ridges

(brain size increases throughout evolution)

characteristics that makes us different from primates

-Bipedalism

-Centrally situated foramen magnum

-S shaped vertebral column

-Short and Broad pelvis

-Femur slants towards the midline keeping knees close

-Strong heels, convergent big toe, divergent toe, longer feet

what is bipedalism

-walking on two legs

Why does bipedalism occur

-10 mya the climate changed Africa dried up causing the habitat to change from forest to savannah and natural selection occured

What are the advantages of bipedalism

-Living in a greater variety of areas (the coast, forests, savannah)

-Upright posture enables the ability to see danger from predators

-see new sources of food and gather food leading to greater brain development leading to language development

-Manipulate objects/environments (gathering food, defense and carrying offspring, make tools with arms completely free)

-Reduce the risk of overheating larger body plan exposed for losing heat

-To walk or run long distances

What is the foramen magnum?

An opening at the base of the skull through which the spinal cord attaches to the brain

Where is the foramen magnum situated?

Centrally under the skull in a forward position

What does the Foramen magnum's forward position allow for?

-the head to be held firmly upright

-the body's center of gravity directly over the legs reducing energy required to balance

-The shoulders bear the weight of the skull allowing humans to walk in a upright posture

Where is the first curve situated?

-In the thoracic region where the vertebral column curves away from the chest

Where is the second curvature situated?

-In the lumbar region where the vertebral column curves towards the stomach

What does the S-shaped curve aid in?

-Keeping the chunk and weight of the body centered above the pelvis acting like a spring, allowing for easy maintenance of the upright position

What does the shape of the human pelvis aid in?

-Supports the legs and trunk in an upright position

-Provides greater stability for walking and running because it allows for efficient weight distribution in an upright position

-Child birth and holding all organs

What does the arrangement of the femur in the body allow for?

-Makes running and walking more efficient

-The angle of the femur is used to identify bipedalism in fossils by anthropologists

What does the calcaneus, convergent big toe, and long feet with stable arch in humans aid in?

- a strong large heel Aids in providing balance for impact and efficient movement.

-Have a convergent big toe ( as we don't need to climb trees)

-longer feet provide better support for whole weight of body and for walking and running

Disadvantages of bipedalism

-Stress on the back resulting in backache

-Shoulder blade no longer acts as a shock absorber

-the narrow birth canal of the pelvis means babies are born small and helpless making childhood longer and more parental care resulting in greater reproductive success as parents have to teach their children for longer. (Zebras are able to walk straight out the womb)

Identifying Bipedalism

-Foramen magnum

-pelvis

-spine

-Brain size

-Dentition

-Prognathism

-Flat face

-Palate shape

-Cranial and brow ridges

How do paleontologists Identify bipedal fossils (F.P.S.)

-By examining the foramen magnum (in a further position suggesting bipedalism)

-Pelvis (if it is shorter and broader then the fossil is bipedal)

-S - shaped spine (suggests bipedalism)

How do paleontologists Identify bipedal fossils (Brain size)

-Climate change was drastic throughout human evolution and therefore a large more complex brain was required for processing new information

-There is an increase in cranium capacity over time in fossils

What did a larger brain allow for?

-Better movement coordination

-Large amounts of information can be processed for decision making

-Speech development, a written language for communication

-Using hands with greater dexterity to make simple tools

- Using and controlling fire

-Humans have more white matter meaning they are able to make more connections since there will be more connections between nerve cells

Three types of evidence that hominid studies depends on

-Fossil evidence (fossilised remains of skeleton)

- Genetic evidence (comparing nuclear DNA, mtDNA)

-Archeology or cultural evidence

How many curvatures does the human vertebral column have?

Two

What is the longest and strongest bone in the body

-The femur (thigh bone)

How do paleontologists Identify bipedal fossils (Dentition)

-Teeth indicate what the species ate and what type of environment they lived in

-(Smaller less sharp teeth cause of fire allows to process food

How do paleontologists Identify bipedal fossils (Prognathism)

-African apes with large jaws that stick out beyond the upper part of the face is called a prognathous jaw.

-Prognathous jaw is evident in australopithecines (EARLY HOMININS)

-The change from prognathous jaw to flat face is partly due to a change in diet, and therefore a change in teeth and facial muscles (our faces do not need large muscles to tear meet)

Features of a prognathous face

-Foreheads slope backwards

-Prognathism

-Brow ridge

Features of a flat face

-Well developed chin

-Brow ridge not prominent

Features of prognathism

-Forehead slopes backwards

-Bones of nose and jaws stick out (Prognathism)

Chewing trend in early hominids

The chewing trend moved from crushing and tearing to crushing and grinding

Why was the need for a diastema eliminated

-A diastema is a gap that accommodates large canines in the mouth.

-The development of smaller teeth made it such that the diastema is no longer a need.

Palate shape (dental arch) in African apes

-Roughly rectangular shape

Palate shape (dental arch) in early hominins

U-shape

Palate shape/dental arch in homo sapiens

-Parabolic curve

What is another name for the cranial ridge and where is it found

-the sagittal crest, found at the top of the skull

What animals or primates have a sagittal crest/cranial ridge?

-Hominids that have a prognathous jaw e.g. Gorillas

What is a brow ridge?

-Bony ridges over the eye sockets

-Is large and developed in African apes and early hominins

-They get smaller in later hominins are greatly reduced and absent in humans

What purpose did the brow ridge serve?

-Served as buttresses against stress exerted by the jaw muscles

-protection for the eyes

What physical changes of early hominins indicate a change in diet?

the reduction of jaw and tooth size is as a result of a change in diet, from raw to cooked food

Eating habits and trends in early-ape like beings

-Ate raw plant and meat matter

-This food required a lot of processing (tearing, biting, chewing)

-Larger teeth (canines)

-Large protruding jaws,

-Cranial and brow ridges that served as attachment for for large chewing muscles

Eating habits and trends in early hominins

-Used tools to cut and grind food before eating

-Large teeth became unnecessary

-Teeth were only required for biting and crushing

-Smaller teeth (canines) and jaws

-Less prognathous skill

-No brow ridges or cranial ridges since muscles were smaller

Human skull shape

-Rounded cranium, smaller brow ridges

Human brain size

Larger (1300 - 1500 cm³)

Human facial features

-Flatter face

-smaller jaw

Human Dentition

-smaller canines

-parabolic dental arch

Human spine shape

S - shapes curve for upright posture

Human Pelvis

Short and broad for bipedalism

Human legs

-Longer legs relative to arms

Human feet

-Arched feet

-non-opposable big toe

Human hands

-Short fingers

-Precision grip

Human Locomotion

-Bipedal walking

Human Larynx position

-Lower in throat

-Enabling complex speech

Human Hair

-Sparse body hair

Ape skull shape

-Pronounced brow ridges, flatter cranium

Ape Brain size

Smaller (300 - 600 cm³)

Ape facial features

-Protruding face

-Larger jaw

Ape dentition

-Larger canines

-Rectangular dental arch

Ape spine shape

-C - shaped curve

-Suitable for quadrupedal movement

Ape pelvis shape

-Long and narrow

-Not optimised for bipedalism

Ape legs

-Shorter legs

-Longer arms

Ape feet

-Flat feet

-Opposable big toe for grasping

Ape hands

-Long fingers

-Powerful grip

Ape locomotion

-Knuckle-walking

-Climbing

Ape Larynx position

-Higher in throat

-Limited vocalisation

Ape Hair

-Dense body hair

Where did hominin evolution take place?

-Took place on the African continent

What could have been driving the force of human evolution

Extreme climate changes that resulted in many extinct plants and animals

What selection pressure allowed hominins to survive?

-The ability to walk upright and larger brains

-Thus being able to deal with changed environment forest to grassland

Which areas did australopithecines occupy (4mya - 1mya)

-Ethiopia, Kenya, Tanzania and South Africa

What is the apparent reason for the emergence of the two dominant australopithecines?

As a result of dietary and habit changes (emergence of fire), a Gracile and Robust form emerged

Gracile form of Australopithecus

-Thin and slender

-Australopithecus africanus and Australopithecus sediba

-Smaller teeth and chewing muscles

-Likely to have led the first humans

Robust form of Australopithecus

-Paranthropus robustus

-Very large jaws and teeth

-Became extinct 1 mya

-Commonly placed in the genus Paranthropus