1. D3 Human Evolution

2. Isotopes and Half Life
Isotopes are alternate forms of an element with different numbers of neutrons and thus different atomic masses
The number of protons is ALWAYS the same!
As long as the atom(s) in question are neutral, the number of electrons are the same as well.

3. Isotopes of Carbon Carbon has 3 isoptoes
C-12 (6 neutrons)
C-13 (7 neutrons)
C-14 (8 neutrons)
Carbon-14 is radioactive; unstable (also called a radioisotope)
C-14 will turn into N-14 (its unstable nucleus gains a proton)

4. Radioisotopes Have an unstable nucleus
They decay! (at a constant rate)
Release energy (radiation) at a constant rate – independent of pressure and temperature
HALF-LIFE: the time it takes for half the radioactive atoms in a sample to decay
The half life of C-14 is 5.6 x 103 years

6. Radioisotopes and Carbon Dating
Because radioisotopes decay at a constant rate, they can be used to date fossils.
C-12 is the most abundant form of carbon
C-14 is found in trace amounts
However, the ratio of C-12 to C-14 in the atmosphere is constant.

7. Carbon Dating
Plants absorb carbon (during photosynthesis) and the ratios of C-12 to C-14 in plants are the same as they are in the atmosphere
Consumers (animals including humans!) consume the plants and the ratio of carbon is the same within our bodies

8. Carbon Dating However, when we die, we cease to consume carbon.
The amount of C-12 in our bodies remains the same
But since C-14 is radioactive, it will decay, and the amount of C-14 in our bodies will diminish

9. Carbon Dating
When analyzing fossils, scientists can determine the age of the fossil by comparing the ratio of C-12 to C-14 in the fossil, knowing the half-life of carbon
The more C-14 the more recent the death of the organism
The less C-14, the more recent the death of the organism

10. Carbon Dating Maximum range for carbon dating is ~50 000 years
In fossil samples older than this, the amount of C-14 is too low to determine the age.
For older artifacts the Potassium –Argon (K-Ar) decay series is used
Radioactive K-40 has a half life of 11.6 x 106 years and decays into Ar-40

11. Humans are Primates
Homo sapiens belong to the order known as Primates

12. Primate Evolution
All primates share a common ancestor about million years ago.
An early branch of the tree shows that primates split into 2 groups: prosimians and the anthropoids.
The anthropoid group then split into monkeys or hominoids (the later within the last 30 million years)

13. Sometime about 50 million years ago continental drift occurred causing South America and the New World to separate from Africa and Eurasia (the Old World)
This explains why there are monkeys in both South America and Africa and why they are similar and show common ancestry

14. Lemurs (ex of prosimians)

15. Old World Monkeys
Snub nosed monkey
Roloway monkey
Vervet monkey

16. White faced Saki monkey
New World Monkeys
Squirrel monkey
White faced Saki monkey
Capuchin monkey

18. Primate Features Primates are a small group of mammals that have:
Large brains relative to body size (large brain allows for increased motor and sensory skills)
Forward facing eyes- stereoscopic vision (3-D) – allowing us to judge distance
We can hold things with our limbs
Opposable thumbs and long, thin straight fingers that allow for fine motor skills to manipulate objects and tools

19. Primate Features Fingerpads and prints Fingernails instead of claws
Shoulder sockets- allow for arms to make complete circles, giving us increased range of movement for greater mobility (such as swinging in trees)
Social dependency – allow for cooperation and group cohesion
See table on page 252

20. Primates are adapted to forest life, tree dwelling
However, some of these characteristics allowed for our pre-human ancestors to exploit new ecological niches when African forests thinned out and dried grassland savannas gave way about 5 million years ago

21. Hominoids - apes No tails
Categorized as gibbons and great apes and humans
One particular branch of apes eventually differentiates into Humans (hominids) and chimpanzees
Humans and chimps share ~98.5 % of their DNA
Our most common ancestor with a chimp lived 6 million years ago.

22. Hominid Fossil Record Modern humans are known as Homo sapiens sapiens
We evolved from early hominids
The course of our evolution can be traced through the fossil record – namely fossils of hip bones, feet, leg bones, footsteps, and skulls
Inferences based on the sizes and morphology of these fossils as wells a artifacts left at burials sites can give insight into our evolution

25. D.3.4: 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.
See table on page 253

27. This simplified cladogram shows the evolution of the homo genus

29. Bipedality (Posture) The ability to walk upright on two feet
Hominids become more bipedal with time
Bipedalism evolved early in hominid evolution
Ardipithecus ramidus may have been bipedal
Australopithecus afarensis is the first fully erect hominid

30. Bipedalism Bipedalism facilitates brain enlargement
allows hominids to carry objects – such as tools or weapons or food
provides increased height – can see predators over tall grasses – and leads to an increased range of vision
Less surface area in contact with the hot African sun

31. Bipedalism
Also aided by the broader and lower pelvis (allows for support of upper body weight when standing upright)
Broad flexible shoulder blade allows free arm rotation during walking.

32. Neoteny Neoteny – the retention of juvenile traits in adults
Ex: flat face and thick skull bones
Ex: Lack of body hair and pigments
Ex: Small teeth
Younger features promoted longer care from the parent, stronger social structuring
Less hair allowed for better non-verbal communication
Later in time (when adults were living past menopause)– younger features represent fertility . More likely to be selected to reproduce

33. Hominid Co-existence
Fossil evidence indicates that one hominid species did not directly evolve into a succeeding hominid species.
Although we are the only hominid species in existence today, at times various hominid species co-existed at the same time

34. Hominid Co-existence
2 mya: Homo habilis and various australopithecines co- existed
(Australopithecines eventually went extinct)
Homo sapiens and Neanderthals (descendants of Homo erectus) co-existed.

35. Cultural and Genetic Evolution
Cultural Evolution:
The changes in the actions and ideas of society including the transmission from one generation to another, via written word, oral traditions, images…
Genetic Evolution:
Refers to the genetic changes that occur.
Can also refer to difference observed between individuals of different racial or cultural groups

36. Cultural Evolution
While genetically, we are only 2% different from a chimp, however, culturally, there are vast differences.
SIMILARITIES:
Ritual behaviours
Symbolic communication gestures
Social organization

37. Richness of Human Culture
6000+ languages
Artistic endeavors
Rituals
Customs
Belief systems
…..

38. Perhaps the most vital component of human culture is language and communication.
FoxP2 gene – codes for a protein that is vital for speech.
(Also involved in facial expressions)
Individuals with a defective copy will have severe speech and language disorders
This gene is found in all mammals
There are only 2 difference in the genetic code for this gene from a human to a chimp.
Therefore, language may be the result of just 2 mutations!

39. Incomplete fossil record
Many missing links in the hominid fossil record
Why?
Dead organisms decompose rapidly
Dead organisms are eaten by scavengers
Soft-bodies organisms do not fossilize easily
Only a small fraction of organisms will have died in conditions favourable to fossilization
And of those that have fossilized, only a small fraction has been discovered thus far.

40. Becoming Human