Evidence for evolution

1. Evidence for evolution HBS3A

2. Biochemistry and Molecular Biology • This involves the study of proteins and DNA in closely related organisms. The fact that closely related species have similar chemistry is seen as further evidence for evolution. • Studies of proteins involve looking at amino acid sequences in common proteins shared by different species • As amino acids are linked in sequences determined by the DNA, differences in amino acid sequences indicate the genetic composition of the organisms. The greater the similarities, the greater the degree of relationship presumed

3. DNA • DNA studies involve the analysis of the nucleotide sequences (gene sequences) • Genetic linkage groups involves looking at groups of genes close together on the same chromosomes • DNA sequencing involves breaking up DNA into chunks to identify the actual sequence of bases in the DNA • DNA hybridisation involves splitting DNA and merging strands from different species to look for differences in the chains • Sources of DNA include nuclear DNA, mitochondrial DNA & chloroplast DNA (plants)

4. Immunology A new technique that has immerged uses immunology to research the degree of relationship between species. This technique involves looking at antigens in different species. The closer the relationship, the more antigens will be had in common

5. Comparative anatomy This refers to • Homologous structures are structures that are similar due to common ancestors on the evolutionary tree Examples include forelimbs of vertebrates • Vestigial structures are reduced structures or remnants of structures once possessed Examples include pelvis of whales, human canine & appendix These structures indicate changes in structure & ancestral link to those possessing full structures One problem with comparative anatomy is the presence of analogous structures, which are structures that are similar to similar selection pressures, not common ancestry Examples include wings of birds and beetles, body shape of dolphins and sharks • Phylogenetic trees are diagrams showing evolutionary relationships

6. Comparative Embryology • Similar organisms pass through similar stages of development. The closer the similarities in the appearance of the embryo/foetus at each stage, the greater the degree of relationship inferred. • Some scientists believe the development from egg to complete organism may reflect the evolutionary history of that organism, as many embryos possess structures which are not found in the adult, but appear in organisms in the ancestral tree eg gill slits and tails in all mammals (including humans)

7. Biogeography • This refers to studies of the distribution of species, which suggest dispersal patterns and evolutionary history • Examples include finches and other animals of Galopagos and other isolated islands, differences between species either side of the Wallace line (Australasia and Asia)

8. Artificial breeding • This refers to human selection by breeding for particular characteristics (artificial selection) • Examples include domestic animals (eg dogs, cats, cows, sheep, pigs, pigeons, etc) and plants (eg wheat, rice, fruit & vegetables) - Brussel sprouts, cauliflower, broccoli and cabbage have all been developed from the Kale plant.

9. Palaeontology • This involves the collection of evidence of past life or fossils The fossil record shows: • similarities between prehistoric organisms and organisms living today eg mammoths & elephants • changes in some species such as horses, whales, pigs • some organisms have changed little throughout their history. This may be due to little change in the selection pressures These organisms are called living fossils eg coelacanth, crocodile, cockroach Some problems with using fossils include incomplete records eg human records problems with dating eg changing CO2 levels affect carbon dating

10. Fossils • Fossils are preserved remains of dead organisms. This includes body parts eg shells, bones, teeth, mummified bodies, pollen and evidence of their presence eg footprints, burrows, copraliths (fossilised faeces) • They provide evidence for evolution because they show sequences of changes in a species eg horse, whale and the presence of species that no longer exist eg dinosaurs

11. Fossil formation Fossils are formed when organisms die and are preserved rather than being eaten or decaying. Fossils that are preserved include shells, bones, skulls, teeth, mummified bodies, pollen, footprints, burrows, copraliths (fossilised faeces)

12. Conditions that favour fossilisation • rapid burial eg by silt, sand, ash, mud, ice, etc so that the organism is not eaten or decayed • exclusion of oxygen eg by burial so that decay is slowed • wet, acidic, oxygen depleted soils eg peat bogs so that decay is slowed (bones are dissolved, but soft tissue mummifies) • dry alkaline conditions eg sand, ash so that hard tissues eg bone and teeth are preserved • The reasons that so few fossils are found are: most dead organisms are eaten or decay, or are destroyed by volcanoes, erosion, etc

13. Fossilisation What sorts of fossils (if any) are most likely to be formed by these events? • a dead tree in a tropical rainforest • a dead elephant washed into an African river • a dead snail on the bottom of a lake • an animal fallen into a peat bog • a mammoth trapped in a glacier • a herd of buffalo walking over volcanic ash • a forest covered by volcanic lava • an insect trapped in pine resin, which is then covered by a mud slide

14. Fossilisation What sorts of fossils (if any) are most likely to be formed by these events? • a dead tree in a tropical rainforest none - decompose • a dead elephant washed into an African river skull, bones, teeth, tusks • a dead snail on the bottom of a lake shell • an animal fallen into a peat bog mummified body with no bones, skull or teeth as these dissolve • a mammoth trapped in a glacier whole preserved animal • a herd of buffalo walking over volcanic ash footprints • a forest covered by volcanic lava none – destroyed by the heat • an insect trapped in pine resin, which is then covered by a mud slide whole insect preserved in amber

15. Dating techniques • Relative dating involves working out the order – which is older or younger eg stratigraphy, index fossils, correlation of strata, fluorine • Absolute dating involves assigning an actual date in years eg carbon dating, potassium argon dating, tree rings

16. Relative dating techniques • Stratigraphy comparing layers – the oldest is on the bottom, the youngest on the top • Correlation of rock strata comparing layers at different sites to match up layers of the same age, then using stratigraphy – oldest is at the bottom • Index fossils using fossils to help match up layers – the fossils need to be widely distributed (found everywhere) for a short period of time (only in 1 or 2 layers) • Fluorine bones insoil absorb fluorine. The longer the bone is buried the more fluorine it absorbs. A bone with less fluorine than another must be younger. It only works on fossils found at the same site as fluorine concentrations are different, and this affects how much is taken up by the fossil • Problems include tectonic events – faulting, folding and erosion - that disturb rock layers. Burials also disturb the position of fossils

17. Absolute dating techniques • Most work on radioactive decay - they lose mass at a constant rate • A half life is the time taken to lose half its mass • Examples of radioactive materials used for dating include carbon-14, potassium-40, uranium series • Other dating techniques include tree rings, fission tracks

18. Using relative dating Identify the site with the oldest strata in each of the following cases: a) Site A Site B Site C b) Site A Site B Site C

19. Using relative dating Identify the site with the oldest strata in each of the following cases: a) Site A Site B Site C Youngest layer Oldest layer b) Site A Site B Site C youngest oldest

20. Using absolute dating 1 • How many half lives does it take to reduce the percentage of original nuclei to 25%? • If this represented a radioactive isotope with a half-life of 1300 million years, what is the age of a sample with 12.5% of the original nuclei left?

21. Using absolute dating 1 • How many half lives does it take to reduce the percentage of original nuclei to 25%? 2 • If this represented a radioactive isotope with a half-life of 1300 million years, what is the age of a sample with 12.5% of the original nuclei left? 3 x 1300 million = 3 900 million

22. Using absolute dating 2 • Calculate the age of a fossil that has a decay rate of 6 nuclei/second. • Assuming the half-life of C-14 is 5730 years, approximately how many half lives have passed? c) Which of the following could be dated by this method? • a human skull? • a stone hand axe? iii) a dinosaur skeleton? iv) a bone found in a layer above one dated at 60 000 years? v) a bone found in a layer below one dated at 100 000 years?

23. Using absolute dating 2 a) Calculate the age of a fossil that has a decay rate of 6 nuclei/second. ~8 000 years b) Assuming the half-life of C-14 is 5730 years, approximately how many half lives have passed? ~ 1.3 c) Which of the following could be dated by this method? • a human skull? Yes • a stone hand axe? No – it doesn’t have organic matter to date iii) a dinosaur skeleton? No – it’s too old iv) a bone found in a layer above one dated at 60 000 years? Yes v) a bone found in a layer below one dated at 100 000 years? No – it’s too old