D.3 human-evolution

HUMAN EVOLUTION

Option D.3IB Biology

Miss Werba

2

THINGS TO COVER

• Absolute dating using radioisotopes• Major physical features that

define humans as primates• Trends in fossils of Australopithecus and Homo• Coexistance of species of the family Hominidae• Incompleteness of the fossil record• Correlation between the change in diet & increased

brain size in hominid evolution• Difference between cultural & genetic evolution

MISS J WERBA – IB BIOLOGY

ABSOLUTE DATING

• Fossils contain isotopes of elements that accumulated in the living organisms.

• An isotope is an atom which has a different mass from most other atoms of the element. The difference is caused by a different number of neutrons.

• If the isotopes are unstable, they will lose protons and break down over time, changing into one or more atoms of other elements and often emitting radiation. This is called radioactive decay.

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ABSOLUTE DATING

4MISS J WERBA – IB BIOLOGY

• Each radioactive isotope has a fixed half-life. • This is the time it takes for the number of atoms of

the isotope or radioactivity to halve.

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ABSOLUTE DATING


• The half-life can therefore be used to date fossils based on the relative concentrations of the reactant and product of the decay.

• Carbon-14 (14C) has a half life of 5730 years so it is useful for dating fossils less than 100,000 years old

• Potassium-40 (40K) has a half-life of 1.3 billions years so useful for long-term dating.

• Error of less than 10%.

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ABSOLUTE DATING

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• Carbon-14 will chemically behave like a regular carbonatom but is somewhat unstable.

• It spontaneously changes into Nitrogen -14 (14N) and emits some radiation.

• 14C is present in small amounts on Earth. • As 14C behaves chemically like the normal carbon, it is

used in photosynthesis and enters the food chain.

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ABSOLUTE DATING


• After the organism dies, the process of incorporating new carbon into the body stops.

• After 5730yrs, the amount of 14C present in the remains is half of what it was at the time of death.

• After 11,460 yrs, it would be a quarter.

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ABSOLUTE DATING


• Essentially, you can calculate the age of the organism by multiplying the number of times that the concentration of the original isotope has halved then multiply that by the half-life.

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ABSOLUTE DATING


REVIEW: CLASSIFICATION OF

HUMANS

Kingdom Animalia Multicellular, eukaryotic organisms; fixed body plan; motile; heterotrophs

Phylum ChordataAt some time in their life cycle, they have a notochord, a hollow dorsal nerve cord, pharyngeal slits, an endostyle, and a post-anal tail.

Sub-phylum Vertebrata Have backbonesClass Mammalia Warm blooded; hair; mammary glands;

Sub-class Eutheria Placental mammals

Order Primates

Adapted for tree-dwelling lifestyle, acute vision, opposable thumbs, sexually dimorphic, slow development rates but long life spans, use a variety of locomotion techniques and social systems.

CLASSIFICATION OF HUMANS


Sub-order Anthropoids A primate that is not a lemurid, lorisid, or tarsier; of “human likeness”

Family HominidaeLarge, tailless primates, sexual dimorphism, quadrupedal (able to use their hands for gathering food or nesting materials or using tools), omnivorous

Genus Homo Includes modern humans and their close relatives

Species Homo sapiens "Wise human" or "knowing human”; bipedal primates

Sub-species Homo sapiens sapiensHighly developed brains, capable of abstract reasoning, language, introspection, and emotion, an erect body carriage; inhabit every continent on Earth, social by nature

CLASSIFICATION OF HUMANS


HUMANS AS PRIMATES

• Most of the features of human beings that link them to primates are adaptations to tree life:– Dexterous hands with opposable thumb and long

fingers – Sensitive fingers with nails – Eyes closer together in front of the face for enhanced

depth perception, excellent eye-hand coordination – A large brain– Shoulder joints that allow movement in 3 dimensions – Shoulder joints and skull modified for upright posture – Parental care with usually single births and long

nurturing of offspring

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HUMANS ARE PRIMATES


• We can move our thumb to a position opposite the fingers.

• Greatly improves the ability to grasp, which is important for tree dwellers.

• Also improves ability to manipulate objects.

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HUMANS ARE PRIMATESTHE OPPOSABLE THUMB


• Tree dwelling allows primates to see further.• Primates have a smaller field of vision so they need

to turn their heads to observe what is going on around them, but their vision is very good.

• The overlapping fields of view (FOV) from the two eyes allows primates to be good at judging distances, vital for moving between branches

• Colour vision helps primates find food.

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HUMANS ARE PRIMATESACUTE VISION


• Primates’ brains are larger than the brains of other animals of the same mass

• Improves ability to manipulate items• Also related to longer care of the young

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HUMANS ARE PRIMATESLARGE BRAIN


• Primate babies are born helpless• The upright position requires modification to the

pelvis and the birth canal which puts restrictions on the size of the baby’s head

• As a result, babies are born helplessand require a long time of care

• This allows them to learn many skills from their parents

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HUMANS ARE PRIMATESPARENTAL CARE


• Primates have several different types of teeth• Allows individual to eat different kinds of food, both

of plant and animal origin

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HUMANS ARE PRIMATESTEETH


THE EVOLUTION OF MAN

• Fossils have been found of various species of the family Hominidae leading to several different speculations about their revolutionary relationships.

• Those of the genus Australopithecus (southern ape) lived from 4 million years ago to 1 million years ago. Their brains were 500cm3 or less and they walked upright.

• Those of the genus Homo lived from 2 million years ago. Their brains are 600cm3 or more and they also walk upright.

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THE EVOLUTION OF MAN


• ie. the root• The earliest fossils found • Remains have been found in Ethiopia (1994)• Lived 4.4 million years ago• Both ape-like traits and Australopithecine-like traits. • Bone sizes indicate that the Ardipithecus species

were the size of a modern chimpanzee. • They walked upright and lived in shady forests.• Teeth are very similar later hominids.

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ARDIPITHECUS RAMIDUS (A. ramidus)


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ARDIPITHECUS RAMIDUS (A. ramidus)


http://upload.wikimedia.org/wikipedia/commons/f/ff/Ardipithecus_kadabba_fossils.jpg

• ie. southern ape from the Afar desert• The earliest fossil found • Lived from 4.0 - 2.8 million years ago• Remains have been found in Ethiopia and Tanzania• They were small individuals that walked upright• They had an ape-like face • Their hands were free • The brains were similar in size to that of a chimp

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AUSTRALOPITHECUS AFARENSIS

(A. afarensis)



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AUSTRALOPITHECUS AFARENSIS

(A. afarensis)


• ie. southern ape of Africa• lived from ~2.5 million years ago• Very similar features to A. afarensis• Bipedal• Did not have large brains• Flatter face• Larger molars for plant based diet

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AUSTRALOPITHECUS AFRICANUS

(A. africaus)



• lived from 2.0-1.0 million years ago• remains have been found in

South Africa• Have massive flat or concave faces • Very heavy build• Relatively long arms• Very large molars, bones and skull• Had a brain capacity ~15% more than A. africanus• Males and females differed markedly in body size

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AUSTRALOPITHECUS ROBUSTUS

(A. robustus)



• Known as the “handy man”, as remains are often accompanied by simple tools

• Many scientists agree that H. habilis probably arose from A. afarensis, around 2.0 million years ago in East Africa

• Smaller teeth and jaw for meatier diet• Size like humans• Brain size and shape more human-like

than A. afarensis

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HOMO HABILIS(H. habilis)



• Lived from 1.0 million years ago • Likely to have arisen in Africa• H. erectus migrated to other parts of the world• Larger brain than H. habilis• Used more complex tools so meat became a

significant part of diet and changed teeth • Java man and Peking man were both

H. erectus fossils

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HOMO ERECTUS(H. erectus)



• Lived from 250,000 to 30,000 years ago• Neanderthals lived mostly in cold climates.• Fossils found throughout Europe & the Middle East.• Had a protruding jaw & a weak chin. • Slightly larger brain than that of modern humans.• Had short, stocky bodies similar in proportion to

those of modern cold-adapted peoples.• Evidence of rich culture – jewellery making; burial of

the dead

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HOMO NEANDERTHALENSIS(H. neanderthalensis)



• Lived from 100,000 years ago • Another wave of immigration distributed H. sapiens

all over the world• Have brains larger than 1000cm3

• Species is distinguished by a sharplyrising forehead, small eyebrow ridges, a prominent chin, and a light bone structure.

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HOMO SAPIENS(H. sapiens)



• H. sapiens sapiens came to Europe separate from the Neanderthals

• One of the earliest fossils found of this subspecies is called Cro-Magnon man

• Had a strong physical resemblance with humans living today

• Suspected to be the first to use language• Large brain, flat face, reduced teeth, and reduced

robustness

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HOMO SAPIENS SAPIENS(H. sapiens sapiens)



• Enlargement of brain • Taller, more erect structure• Pelvis shorter and broader to support organs in

walking and to attach walking muscles. • Legs become stronger and longer, while arms

become shorter and weaker. • Knee can now be fully straightened. • Foot forms more of a platform and rigid shape

without opposable toe.

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HOMO SAPIENS SAPIENS(H. sapiens sapiens)



• Fossils have been dated at 6.0 million years ago!• The species is by far the oldest-known member of

the family to which humans belong• O. tugenensis lived near the time when genetic

analyses suggest our oldest hominid ancestor split from the oldest ancestor of the great apes.

• There's a chance O. tugenensis could be the proverbial "missing link" -- or at least one of them.

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ORRORIN TUGENENSIS (O. tugenensis)



4 3 2 1 0millions of years ago

A. afarensis

A. africanus

A. robustus

H. habilisH. erectus

H. heidelbergenesis ↓

H. neanderthalensis

H. sapiens

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EVOLUTION OF MANProposed model of human evolution


THE EVOLUTION OF MAN:

SUMMARISED

• Humans have the largest brain size (in relation to body mass) and therefore have a bigger skull.

• Cranium size has increased rapidly during hominid evolution.

• Brow ridges present in other hominids are not present in humans.

• The hole that allows the spinal cord to leave the skull (foramen magnum) is further underneath the head in humans than in the great apes.

• Forward facing eyes.

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EVOLUTION OF MANSKULL & BRAIN SIZE



• U-shaped jaw replaced by a V-shaped jaw.• Conical canines have disappeared.• Molar size has been reduced (vegies/plants meat)

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EVOLUTION OF MANTEETH & JAWS



• Modern hand is able to grasp & pick up objects b/w the thumb & fingertips

• Opposable thumb – highly mobile joint• Humans have relatively long fingers.• Wrist can rotate.• Very sensitive palms.

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EVOLUTION OF MAN HANDS



• More barrel-shaped ribcage (b/c arms no longer used for locomotion)

• Human vertebral column has a curve at neck & lower back

• Broader & lower pelvis than the great apes• Longer legs than arms• Lower centre of gravity• Broad, flexible shoulder blade for free arm rotation• Fully extendable legs for walking• Non-opposable big toe

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EVOLUTION OF MAN SKELETON, LOCOMOTION & POSTURE



• Neoteny = retention by adults of juvenile traits• Neoteny slows or delays the development of an

animal or organism• Possible juvenile human characteristics:

– Flat face & thin skull bones– Lack of body hair & pigmentation– Small teeth– Prolonged growth period– Long life span

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EVOLUTION OF MAN NEOTENY



COEXISTENCE OF HOMINID SPECIES

• Trends do not indicate that one species superseded another.

• Homo habilis coexisted with the various species of australopithecines for ~2 million years, before the australopithecines became extinct.

• Homo erectus was also present before the australopithecines became extinct.

• Homo erectus was the common ancestor for both Neanderthals and Homo sapiens.

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COEXISTENCE OF HOMINIDS



• The coexistence of the various hominids was probably because they occupied different ecological niches.

• Most Neanderthals became extinct relatively suddenly, probably because of competition with Homo sapiens.

• It is possible that there was gene flow and the Neanderthals were absorbed into the Homo sapiens lineage.

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COEXISTENCE OF HOMINIDS



INCOMPLETENESS OF THE

FOSSIL RECORD

• From 200,000 to 150,000 years ago, only a few Neanderthals survived the cold.

• As a result, only very few fossils are found.• Only a very few remains will ever be fossilised, so if

not many individuals were alive at any one time, the chance of leaving fossils becomes small.

• And then we have to find them....

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INCOMPLETENESS OF THE FOSSIL RECORD



• So the fossil record of human ancestry is incomplete and thus we cannot certainly determine when certain species originated and became extinct.

• The early fossil record is fragmented and scarce because: – dead organisms decompose rapidly– Dead organisms are eaten by scavengers so bones

were spread – they were not buried– few died in location where they would be preserved

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• As there are ‘missing links’ it can not be ensured that the hypothesised evolution of hominids is accurate.

• However, punctuated equilibrium suggests that these gaps are to be expected from the process of speciation.

• It means that the “missing links” might exist, but are in such low numbers that it makes them harder to find.

• Every new discovery could potentially change the current understanding of hominid evolution....

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CHANGING DIET &

BRAIN SIZE

• The costs of this larger brain size were:– A longer gestation period– Extension of prenatal, parental care– Increased energy requirements for both mother

& child• The trend for an increased brain capacity continued

as these individuals survived better and reproduced.

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CHANGE IN DIET & BRAIN SIZE



• This was made possible by hominids progressing from an omnivorous diet to a more carnivorous diet.

• The larger brain would have also helped the hunting & killing of animals.

• The climate was also becoming drier, meaning that the edible vegetation became more difficult so adding meat to the diet might have been a necessity.

• This also allowed them to migrate since they were no longer dependent on familiar plants.

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CHANGE IN DIET & BRAIN SIZE



GENETIC & CULTURAL EVOLUTION

• Genetic evolution: – involves the change of genetic material

which is subsequently passed on– the change is random– whether the change is an improvement is dictated

by the environment– the skills acquired are not passed on through the

genes so the child of a great hunter would not know how to hunt unless it was taught

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• Cultural evolution: – the accumulation of useful skills and knowledge,

and the discarding of harmful practices, passed down through thousands of human generations

– based on the fact that we have elaborate language skills

– accumulated experiences can be passed on from one generation to another using verbal and written language

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• The evolution of speech and the reflective mind (consciousness) occurred at the same time in the Homo lineage

• Recent finds suggest that Neanderthal man had the anatomy that allowed speech and they hunted in groups, which would have required excellent communication.

• Larger brains capable of speech would have needed a diet full of meat in order to sustain the energy requirements. Australopithecus was vegetarian.

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• The oldest tools are 2.6 million years old, coinciding with the increase in brain size. This allowed them to work out plans for using the tools to obtain more food.

• Neanderthals may have had religion. They buried their dead with flowers and tools which could suggest that they believed in an afterlife. No evidence of art per se but beads have been found which would only have served a decorative function.

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• Cro Magnon (Modern Man) painted drawings of animals on the walls of their caves. They had elaborate art which is possibly related to a form of religion.

• Cultural evolution led to domestification of animals and agriculture around 10,000 years ago.

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• Cultural evolution has spanned millions of years in three major stages: – the nomadic (hunting)– agricultural (settled)– and industrial ages

• However, we have not changed biologically in any significant way. We are probably not any more intelligent than the cave men. Our increased ability is due to the past experience we draw on.

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Education

D.3 human-evolution