IB Biology
Option D
D3 Human Evolution
All syllabus statements ©IBO 2007
All images CC or public domain or link to original material.
Ms. Fargo
Courtesy of
Jason de Nys
http://commons.wikimedia.org/wiki/File:LB1_skull.jpg
http://commons.wikimedia.org/wiki/File:Human-evolution.jpg
D.3.1 Outline the method for dating rocks and fossils using radioisotopes, with reference to
14C and 40K.
14C
14C
Decay
Formation
(Pronounced Carbon 14)is a naturally occurring isotope of carbon with a half life of
5730 years
It is constantly being made in the atmosphere when cosmic rays cause neutrons to fuse
with nitrogen nuclei and “kick out” protons
production is in equilibrium with its decay to 12C
The 14C is incorporated in carbon dioxide which is then taken
up by plants. In the end all living things have the same ratio of
14C to 12C
When an organism dies it no longer takes in 14C. So over time
the ratio of 14C to 12C changes. This is measurable and can be
used to estimate age.
The limit for accurate determination of age is about 50,000y
Radioactive Dating game
http://phet.colorado.edu/en/simulation/radioactive-dating-game
http://en.wikipedia.org/wiki/File:Carbon_14_formation_and_decay.svg
40K
is an isotope with a half life of 1.3 X 109 y
It decays to 40Ar.
When 40K is released from a volcano in lava all of the
argon gas is driven off.
So brand new rocks effectively have a ratio 40K: 40Ar of
100:0
Over time the lava may be weathered and eroded and
incorporated into sedimentary rocks.
The measured ratio of 40K to 40Ar can be used to date
rocks over one million years old with an accuracy of
around 50,000 years
http://www.youtube.com/watch?v=ErgdpG_N9vQ
D.3.2 Define half-life.
The time it takes for
half of a radioactive
isotope to decay
Simulation of many identical
atoms undergoing radioactive
decay, starting with either four
atoms (left) or 400 atoms (right).
The number at the top indicates
how many half-lives have elapsed
http://en.wikipedia.org/wiki/File:Halflife-sim.gif
http://en.wikipedia.org/wiki/File:Plot-exponential-decay.svg
What is the half life for each of the
isotopes represented by these curves?
?.??
0.13
0.7
3.42
D.3.3 Deduce the approximate age of materials based on a simple decay curve for a
radioisotope.
D.3.4 Describe the major anatomical features that define humans as primates.
human
gibbon
gorilla
Grasping pentadactyl limbs
Adaptation for a tree-living (arboreal) existence with
prehensile (grasping) hands, five digits (four fingers plus an
opposable thumb) manipulating objects
http://www.flickr.com/photos/johnkay/5901639745/
http://www.flickr.com/photos/shannonkringen/5466678956/
http://www.flickr.com/photos/grendelkhan/1160017887/
Binocular Vision-- vision in which both eyes are used together.
An increasingly forward-facing position of the eyes with the
development of stereoscopic vision and both sides of the brain
receive images from the two eyes, enabling accurate depth
perception
Monkey
Reduced
snout
leading to
reduced
olfaction
Squirrel
vs.
Doggie
Human
http://www.flickr.com/photos/21185968@N00/3760968061/
http://www.flickr.com/photos/tomitapio/4566585948/
http://www.flickr.com/photos/aechempati/5419119893/
http://www.flickr.com/photos/tambako/4561359690/sizes/l/in/photostream/
Human
Baboon
Gorilla
Generalised
Dentition
Moo
Cown
http://www.flickr.com/photos/philman/275506
http://www.flickr.com/photos/patries71/31498
http://www.flickr.com/photos/mugley/3280473
http://www.flickr.com/photos/plasticbrain/424
Human hands are adapted for grasping and fine
manipulation. In contrast gorillas have short fingers for
knuckle walking and gibbons have elongated fingers and
reduced thumbs for brachiating.
http://www.flickr.com/photos/docsearls/5500125757/
http://en.wikipedia.org/wiki/File:Western_Lowland_Gorilla.jpg
http://www.flickr.com/photos/cskk/2709688102/
Others:
-Forelimbs able to twist--long, slender limbs that rotate freely at
shoulders and hips
-Nails instead of claws, and sensitive touch pads at the ends of the
digits
-Clavicle allows wide range of arm movement
(re. the above two points: if you have a gentle and patient pet dog,
give it a rub on the tummy and then move it’s forelegs, they really only
move in one plane)
Slower reproduction
- long gestation
- usually one offspring at a time
Larger skull – relative to body size
Large brain – more complex, more folds
Better visual acuity – more of the photoreceptors have their own
sensory neurons
Social dependency
--An expansion and elaboration of the parts of
the brain, especially the parts associated with
muscular co-ordination, colour vision, tactile
senses, memory, thought, learning, sound
processing
--tendency to hold the head erect and to sit
upright
D.3.5 Outline the trends illustrated by the fossils of Ardipithecus ramidus,
Australopithecus including A. afarensis and A. africanus, and Homo including H. habilis,
H. erectus, H. neanderthalensis and H. sapiens.
Hominidae is a family within the order Primata which is defined by bipedal
locomotion
Trends in hominid evolution:
Increasing adaptation to bipedalism, especially forward movement of foramen magnum
increasing brain size in relation to body size
Ardithecus ramidus
• Lived approximately 5.8-4.4 MYA in Ethiopia
• Believed to be very close to the split between line of
organisms that became more human like and the line
which became more chimpanzee-like
• Most fossils of these organisms are teeth
• Similar to chimps but a few striking hominid features
– Molars show ape-like characteristics (length is longer than
the breadth)
– Canine teeth more hominid like (not sharp, shorter, and
less projecting than ape-like canines)
• Fossil evidence indicates bi-pedalism is possible
Australopithecus afarensis
(Southern ape of the Afar region)
• 4-2.5 MYA in Eastern Africa
• “Lucy”—remains dated 3.5 MYA
–
–
–
–
–
110 cm tall and 30 kg
Tall lower jaw
Fairly large molar teeth
Projecting face
Bi-pedal but walk was most likely more ‘rolling’ than
ours
• Cranial capacity was 380-430 cm3
Australopithecus afracanus
(Southern Ape)
•
•
•
•
•
3-2.5 MYA
Tall, thick lower jaw
Large molars
Projecting face
Cranial capacity was 435-530 cm3 (cranial capacity is larger)
– Brain of Australopithecus was about one-third the size of a
modern human's.
• Walked fully erect and
• had human-like hands and teeth.
Homo hablis
(Handy man)
• Unearthed first in Olduvai Gorge in Tanzania
(Northern Africa)
• Later discovered in Kenya, Ehtiopia, S. Africa
• 2.4-1.6 MYA
• Flatter face and larger molars than
Australopithecus
• Cranial capacity still only 600 cm3
• Used simple tools and fire
• Lived in caves
Homo erectus
•
•
•
•
•
•
1.8 MYA – 100,000 YA
Smaller jaw
Receding forehead
Large brow ridges
Smaller molars
Cranial capacity 1000 cm3
Homo neanderthalensis
(Neanderthal man)
• Lived in Europe and Western Asia 200,000 to
30,000 years agoa
• Smaller jaw
• Lower forehead
• Smaller brow ridges
• Smaller molars
• ***ODDITY***They had larger brains than
modern humans (up o 1600 cm3)
Homo sapiens
•
•
•
•
•
•
•
•
•
Archaic forms date back to 140,000 to 70,000 YA
Lived in Africa, Europe, Asia
High Forehead
No brow ridges
Flat face
Small molars
Very small jaw
Bury their dead
Cranial capacity 1300 cm3 (similar to humans today)
Synopisis
•hominids originated in Africa and spread to other continents
Ardipithecus fossils found in Ethiopia
Australopithecus and Homo habilis fossils found in Southern and Eastern
Africa
Homo erectus fossils found in Eastern Africa and in Asia
Homo neanderthalensis fossils found in Europe
Homo sapiens fossils found in all continents except Antarctica
decreasing relative size of: face, jaw, teeth, esp. canines; increasing
relative size of brain case, forehead
http://commons.wikimedia.o
http://commons.wikimedia.o
http://commons.wikimedia.o
http://commons.wikimedia.o
http://commons.wikimedia.o
http://commons.wikimedia.o
http://www.flickr.com/photo
Ardipithecus
ramidus
Homo habilis
Australopithecus
afarensis
Homo erectus
Australopithecus
africanus
Homo
neanderthalensis
Skulls not
to scale
Homo sapiens
1. Gorilla
2. Australopithecine
4. Neanderthal (La-Chapelle-au-Seine)
6. Modern human
3. Homo erectus
5. Steinheim Skull
http://commons.wikimedia.org/wiki/File:Craniums_of_Homo.svg
From the previous two slides you can see:
• enlargement of the brain case
• shortening of the face
• Loss of brow ridges
You can’t really see it but the hole in the bottom of the
skull where the spinal cord exits the brain (foramen
magnum) is further forward in modern humans. This
distributes the weight of the head over the spine so that
modern humans do not need huge necks muscles.
Homo sapiens
Pan troglodytes
(chimpanzee)
http://pandasthumb.org/archives/2006/09/fun-with-homini.html
http://commons.wikimedia.org/wiki/File:Human_and_chimp_brain.png
The jaw has developed from
a U into a V shape. Teeth
have generally reduced in
size. (Chimpanzee provided for comparison)
Skeleton, locomotion and posture
Human knees aligned under the body’s centre of gravity because
femurs are angled inwards.
Human legs straighten completely when walking.
Human spine has additional curves to keep centres of mass of head
and trunk aligned for bipedalism.
Big toe not opposable in humans,
which allows for an arched foot.
Ratio legs:arms greater for humans than other apes
Human pelvis broader