D.3 human-evolution

Option D.3
IB Biology
Miss Werba

• 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 2

D.3.1
D.3.2

• 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.


D.3.1
D.3.2

• 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.


D.3.1
D.3.2

• 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%.

MISS J WERBA – TERM 3 2011 6

D.3.1
D.3.2

• Carbon-14 will chemically
behave like a regular carbon
atom 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.


D.3.1
D.3.2

• 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.


D.3.1
D.3.2

• 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.


Multicellular, eukaryotic organisms; fixed body
Kingdom Animalia
plan; motile; heterotrophs
At some time in their life cycle, they have a
notochord, a hollow dorsal nerve cord,
Phylum Chordata
pharyngeal slits, an endostyle, and a post-anal
tail.
Sub-phylum Vertebrata Have backbones
Class Mammalia Warm blooded; hair; mammary glands;
Sub-class Eutheria Placental mammals
Adapted for tree-dwelling lifestyle, acute
vision, opposable thumbs, sexually dimorphic,
Order Primates slow development rates but long life spans,
use a variety of locomotion techniques and
social systems.


A primate that is not a lemurid, lorisid, or
Sub-order Anthropoids
tarsier; of “human likeness”
Large, tailless primates, sexual dimorphism,
quadrupedal (able to use their hands for
Family Hominidae
gathering food or nesting materials or using
tools), omnivorous
Includes modern humans and their close
Genus Homo
relatives
"Wise human" or "knowing human”; bipedal
Species Homo sapiens
primates
Highly developed brains, capable of abstract
reasoning, language, introspection, and
Sub-species Homo sapiens sapiens
emotion, an erect body carriage; inhabit every
continent on Earth, social by nature


D.3.3

• 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

D.3.3

• 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.


D.3.3

• 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.


D.3.3

• 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


D.3.3

• 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 helpless
and require a long time of care
• This allows them to learn many skills
from their parents


D.3.3

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


D.3.5

• 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.


D.3.5

• 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.


D.3.5


D.3.5

• 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


D.3.5


D.3.5

• 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


D.3.5

• 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

D.3.5

• 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


D.3.5

• 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


D.3.5

• 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


D.3.5

• 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 sharply
rising forehead, small eyebrow ridges,
a prominent chin, and a light bone
structure.


D.3.5

• 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

D.3.5

• 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.

D.3.5

• 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.


D.3.5

H. sapiens
H. neanderthalensis

H. heidelbergenesis
↓

H. erectus
H. habilis

A. afarensis

A. africanus
A. robustus
4 3 2 1 0
millions of years ago


D.3.5

• 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.


D.3.5

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


D.3.5

• 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.


D.3.5

• 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

D.3.5

• 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


D.3.6

• 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.

D.3.6

• 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.


D.3.7

• 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....


D.3.7

• 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


D.3.7

• 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....

D.3.8

• 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.


D.3.8

• 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.

D.3.9
D.3.10

• 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


D.3.9
D.3.10

• 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


D.3.9
D.3.10

• 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.


D.3.9
D.3.10

• 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.


D.3.9
D.3.10

• 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.


D.3.9
D.3.10

• 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.


D.3 human-evolution

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