IB Biology
Option D
D3 Human Evolution
All syllabus statements ©IBO 2007
All images CC or public domain or link to original material.
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
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
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 50000 years
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
http://www.flickr.com/photos/johnkay/5901639745/
http://www.flickr.com/photos/shannonkringen/5466678956/
http://www.flickr.com/photos/grendelkhan/1160017887/
Binocular
Vision
http://www.flickr.com/photos/kevenlaw/2260970300/
http://www.flickr.com/photos/tambako/5289604279/
http://www.flickr.com/photos/patries71/3038074728/
http://www.flickr.com/photos/pezz/447411079/
http://www.flickr.com/photos/maessive/62526827/
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
Others:
Forelimbs able to twist
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
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.
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)
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/
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
retention, by adults in a species, of traits previously seen
only in juveniles. (Wikipedia)
Some human characteristics thought to be a result of neoteny.
• Lack of body hair
• Small teeth and reduced numbers of teeth
• Prolonged growth period
• Long life span
• Flat face and thin skull bones
• Lactase production in adults
• Epicanthic eye fold
• Small nose
• Longer trunk relative to arms and legs
D.3.6 State that, at various stages in hominid evolution, several species may have coexisted.
http://en.wikipedia.org/wiki/Human_evolution
Note that according to this
interpretation of the fossil
record Homo sapiens is not
descended from Homo erectus
or Homo neanderthalensis.
However, some postulate that
Homo sapiens may have
hybridised with Homo
neanderthalenis.
This could have contributed to
the disappearance of the
neanderthals in much the
same way that indigenous
animals like dingos are in
danger of extinction due to
breeding with domestic dogs.
http://en.wikipedia.org/wiki/File:Humanevolutionchart.png
TOK
Read the article on Wikipedia
about Homo floresiensis
Discovered in 2004 on the
Indonesian island of Flores, it
has stirred up controversy in
the palaeoanthropological
world. Is it a separate species
or is it the remains of diseased
Homo sapiens. You be the
judge!
Short PBS video
D.3.7 Discuss the incompleteness of the fossil record and the resulting uncertainties about
human evolution.
It isn’t easy to create a collection of fossils that clearly
show the change of species from one to another.
Fossils rarely result when an animal dies for the
following reasons:
• Decomposition is usually rapid; soft body parts are
rarely fossilised
• Scavengers usually break up skeletons and even
chew up bones
• The conditions have to be just right for fossilisation
to occur.
• Only a tiny, tiny, tiny fraction of all of the fossils in existence have been found.
Skulls and teeth are usually the parts of
the ancestral hominids that survive to be
fossilised and found
Therefore there is a lot of conjecture as
to where they all fit in the family tree.
Hypotheses are often overturned by new
discoveries that rewrite the relationships
between the species.
http://www.flickr.com/photos/brentdanley/2205021283/
The large gaps in the human evolution
fossil record are consistent with
punctuated equilibrium
The following four slides show how the
gaps are filled over time with new
discoveries. The graphs plot cranial size
against the age of the fossil.
http://www.flickr.com/photos/prfr/3196435827/
1850
1950
1900
2002
http://en.wikipedia.org/wiki/Transitional_fossil
Despite the fossil evidence we have so far,
there are still large gaps in our knowledge
We have no
fossil for the last
common ancestor
of humans and
chimpanzees
It is believed to
have lived 6-8
million years ago
Find out how this
estimate was determined
http://www.flickr.com/photos/owenbooth/126288240/
D.3.8 Discuss the correlation between the change in diet and increase in brain size during
hominid evolution.
The benefits of a bigger brain include:
• More complex tools
• Mastery of fire
• Cooking
• Wamth
• Protection
• Greater behavioural flexibility (less
reliance on instinct and better able
to learn and pass on knowledge
necessary to adapt to an
environment)
http://madsenworld.dk/anigif/light/flames.gif
http://commons.wikimedia.org/wiki/File:Miscellaneous_stone_tools.jpg
The cost of having a big brain:
• Longer gestation period
• Years of development before
young can look after themselves
• Much more brain development
occurs post birth that for any
other animal
In summary: Big brains are
energetically expensive. The
mother must take in lots of energy
not only during pregnancy, but for a
significant time after.
Hominids needed to increase their
energy uptake.
http://www.flickr.com/photos/superbomba/2288271254/
The solution to this energy crisis
was to swap a diet of these:
http://www.flickr.com/photos/heydrienne/22080973/
For some chunks of this:
The increase in brain size
observed in hominid
fossils has been closely
correlated with an
increased intake of meat.
A bigger brain made
hunting and killing easier
D.3.9 Distinguish between genetic and cultural evolution.
Well gosh, we know all about genetic evolution
by now! In this context it refers to the genetic
changes that have occurred during the evolution
of hominids. e.g. increased brain size, spine
shape, position of knee
Cultural evolution is the changing of ideas held and
actions carried out by societies and the transmission
of these ideas through social learning from one
generation to the next.
e.g. the use of fire, agriculture, tools, weapons,
religion, beliefs
D.3.10 Discuss the relative importance of genetic and cultural evolution in the recent evolution
of humans.
TOK
Read this article:
Are We Still Evolving?
What do you think of the
arguments for and against
this proposition?
The 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
could take a baby from 80,000 years ago,
raise it in a modern environment and it
would be indistinguishable from other
humans in terms of intelligence and
social capabilities.
http://www.flickr.com/photos/wallyg/415498335/
Further information:
Excellent site!