6.
2.
Fossil Record and Dating
The fossil record for hominins is extensive but very fragmented. Remains of hominins have been found in
Africa, Asia and Europe, often accompanied by the remains of other animals (e.g. prey mammals) and, for more recent forms, stone tools.
The most common and important fossils are:
 skulls / skull fragments including teeth (hard enamel more resistant to erosion)
 leg bones, especially knee joint, are important for determining bipedalism
Questions:
1. Where have hominins remains been found?
Africa, Asia and Europe
Why would finding teeth in a skull be important?
3.
Give indication of diet
Why would finding knee joints bee important?
Give indication of bipedalism
Dating methods for fossils has got more extensive and accurate over the years, with genome analysis now providing important evidence.
5.
4.
Important dating techniques include:
 location in strata - younger fossils are on top, older bone below (unless rock in strongly folded)
 index fossils - species whose evolutionary time span is known, can give an indication of age if they are in the same rock layer as the hominin fossil e.g. rodent species
 radio carbon dating - measures the amount of carbon -14 remaining in materials that were assimilating it - for sample that are organic rather than mineralised - can only be used on samples less than 60 000 years old
 potassium-argon dating (K-Ar dating) – used for rocks and minerals (not fossils) from 10 000 to 100 million years old – potassium is present in sufficient quantities only where volcanic activity occurs
 electron spin resonance - used for rocks, bone, teeth, coral , eggshells – uses radiation to separate electrons from atoms, changing the magnetic field in a predictable way that can date an item
What type of dating would be useful for bones and teeth?
Radio carbon dating, electron spin resonance
What type of dating would be useful for rocks and minerals?
Potassium-argon dating, electron spin resonance
What is an index fossil?
A species whose evolution is known, can be used to date hominin fossil if found together

Genome Analysis
DNA Sequencing :
 both mitochondrial and nuclear DNA

allows comparisons to be made between the genomes of different species
 the fewer the differences in the sequences, the more closely related are the individuals / populations / species
Mitochondrial DNA – mtDNA:

DNA found in the mitochondria (not in the nucleus)
 is inherited from the egg cell / ovum as the egg has cytoplasm that contains mitochondria while sperm does not
 mtDNA is inherited from the mother only – not the father
 meiosis does not impact on inheritance of mtDNA
 changes in mtDNA from generation to generation are from gene mutations
 changes occur at a steady rate
 provide useful tool for tracing ancestry and determining relationships
Y chromosome DNA:
 a short chromosome with few genes
 not as prone to crossing over as other chromosomes
 only sperm contain the Y chromosome
 inherited from father to son only – down male lines of families
 inherited largely unchanged over generations
 can be used to trace ancestry and determine relationships like mtDNA
Protein analysis
 proteins evolve slowly, so comparing amino acid sequences can indicate how closed related two species are
8.
7.
9.
What is mtDNA?
Mitochondrial DNA
Where is mtDNA found? in mitochondria
How is mtDNA inherited?
From mother only
10. How do changes occur within mtDNA?
By mutation

11. What is Y chromosome DNA?
DNA that make up the genes on the Y chromosome
12. Where is Y chromosome DNA found?
In sperm
13. How is Y chromosome DNA inherited?
From father only
14. Do changes occur within Y chromosome DNA?
No
Fossil Comparisons
Comparisons of fossils are made to identify species ( some sources give over 20 different hominin species) and determine relationships. Paleoanthropologists are scientists who study human fossils. Information from different sources may vary as new evidence is found and interpretations are developed. It is important to access information from the most recent sources.
Exercises:
15. Describe three traditional ways of dating fossil remains.

By which strata the fossils are in – older the strata, the older the fossil

By carbon-dating organic matter if remains are < 60 000 ya

By K-Ar dating the volcanic rocks etc. that the fossils are found in

By presence of index species with the fossils
16. Suggest a possible method for dating or relating each of the following samples: a. some charcoal from an ancient fire b. radiocarbon dating a skull portion found in rock strata beside a stone axe c. d. age of the stone axe a leg bone found in rock strata that also contain a rare, extinct, mollusc fossil use of mollusc fossil as an index fossil rock thought to be nearly 1 million year old potassium-argon dating e. the genetic history of a person from Indonesia compared with a person from Fiji
DNA sequencing / mtDNA comparison / protein analysis
17. Explain how modern genome analysis has helped in analysing the evolution of hominins.

Genome analysis has allowed scientists to compare the base sequences of DNA of different fossils / species to ascertain how closely related they are (the more DNA in common, the closer the relationship); possible times of divergence / ancestry; whether interbreeding occurred. DNA evidence has added significant support to evidence obtained from comparison of skeletal fossil remains.
18. Scientists have proposed that all humans living today have descended from a single woman who lived in Africa about 160 000 years ago; she is known as ‘mitochondrial Eve’. They have also proposed that all living men have descended from one man who lived about 140 000 years ago ; he is known as ‘Y chromosome Adam’. a. Suggest why these two early humans were given these names.

The names Eve and Adam have come from the first humans named in the Bible

Eve is given as ’mitochondrial’ because she has been derived from comparison of mtDNA in females

Adam is given as ‘Y-chromosome’ as he has been derived from comparison of Y-chromosome
DNA in males b. Explain why mtDNA has become so important in investigating evolutionary relationships. mtDNA is present in egg (not sperm) and is not subject to the events of meiosis the mix up the genes – the only changes to mtDNA from generation to generation are random gene mutations which occur at a steady rate, so can be used to provide evidence for relationships and times of divergence between different populations / species
19. ‘Fossil evidence is fact, so is not disputed; it is the interpretation of the fossil evidence that is disputed’. Explain this statement.
Fossils are remains that can be identified by all scientists e.g. structure / function such as knee joint, cranial capacity, tooth type – therefore are not disputed. What the fossils tell us about whom they belong to and how they are related to other fossils is interpretation and this is what differs among scientists, accounting for the wide range of species identified and their degree of relationship / ancestry
20. Scientists often disagree about the classification of hominin fossils and especially about their associated culture. Suggest two reasons for the difficulty in interpreting fossil evidence.
Fossils are rare; remains often damaged; parts may be missing, separated or mixed; ideas about cultural evolution can only be deduced from fossils
21. Suggest reasons why the wide difference in numbers of hominin species given by different paleoanthropologists.
 accounted for by differences in the way the scientists interpret the fossil remains
 some see the variation in the remains as being part of natural variation within a species – these scientists will give few different species in their phylogenetic trees

some believe variation are sufficiently different to place the fossils in different species – these scientists will list many different species in their phylogenetic trees