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EVIDENCE FOR EVOLUTION

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LIFE SCIENCES

EVOLUTION

COURSE

MAY

2010

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Palaeontology

Comparative Anatomy

Comparative Embryology

Comparitive Biochemistry

Biogeography

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Palaeontology – study of plant/animal fossils Palaeontologist – scientist who studies fossils. Fossils - Remains, imprints, traces of organisms that are

usually preserved in rocks. Fossilisation – entire process by which dead organisms or

their parts are transformed into fossils. Fossil record: The observed remains of once-living

organisms taken as a whole.

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http://kim.wits.ac.za/index.php?module=news&action=viewstory&id=gen11Srv0Nme53_81569_1270732348

FOSSIL EVIDENCE

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Fossils are most commonly found in sedimentary rocks. Sedimentary rocks are formed when clay and sand

particles (SEDIMENTS) are carried from one place to another by water/wind - they pile up.

Sediments harden over years because of the weight of overlying sediments and form shale, sandstone and limestone.

Fossils are also found in other places e.g. tree resin, ice etc.

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Plant/animal dies and rapidly covered with sediments Soft tissues decay with the help of micro-organisms Hard body parts e.g. bone, teeth, shells etc. remain intact

as organic material is hardened or replaced by minerals. More layers of sediments form over years Layers compressed Sediment solidifies and forms sedimentary rock Movement of earth pushes sedimentary rock to the surface Fossils exposed to surface by erosion of rock layers.

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Fossils offer evidence of previous life on earth- geological time scale

Fossils help us find out the progressive changes within an animal or plant group.

Age of geological strata. Information about climate and environment.

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Body fossils – complete organisms preserved in ice, resin etc. OR parts of the organism e.g. shells

Cast fossils – Hard parts decomposes and leave and imprint or mould. Mould filled with minerals

Trace fossils - signs or marks of organism that lived previously e.g. fossilized footprints

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Conditions for fossilisation not favourable All fossils were NOT found yet All organisms are not fossilised – some are eaten by

predators, some decay quickly Incomplete fossils Problems in identifying fossils

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Relative dating – sedimentary layers laid down first are the oldest, those laid down last is younger.

Radiometric dating – Decay of radioactive elements/isotopes

Halflife – rate of decay of a radioactive isotope, amount of time it takes to break down half of the atoms of radioactive material to its decay product

Oldest sediments

Parent daughter

Most recent sediments

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Radioactive isotope

Halflife

238U decays to 206Pb 4500 million years

14C decays to 14N 5 730 years

234U decays to 207Pb 704 million years

Question:

The halflife of 14C is 5 730 years and the halflife of 234U is 704 million years. Explain which of 14C or 234U should be used to calculate the age of dinosaur fossils.

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Uranium will be used because dinosaurs became extinct approximately 65 million years ago and 14C can only measure up to 5 370 years ago.

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During each equal time unit, one half-life, the proportion of parent atoms decreases by 1/2

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When embryos of vertebrates are compared to one another in an early stage, they show a number of similarities

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Earnest Haeckal (1834 – 1919) - claimed that “the development of an individual (ontogeny) reflects the stages through which the individual’s species has passed during its evolution (phylogeny)” The different stages in early development of an organism correlates with the adult forms of that organisms’ ancestors.

The idea is that vertebrates developed from a common ancestor

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Name characteristics shown by embryos of different vertebrates that scientists use as evidence that these animals might have a common ancestor

Gill slits, tail, notochord, fish-like heart

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Homologous structures – structures that are similar in structure but may have different functions e.g. forelimbs of most vertebrates, indicative of common ancestry

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Analogous structures – structures that differ in structure but resemble each other in function e.g. wings of birds and butterflies – not related

Wings

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Vestigial structures – structures diminished over evolutionary time, no longer perform the same function as in other organisms, must have been important in some ancestral form but became redundant in later species e.g. vestigial hind limbs of whales.

Hindlimb

femurpelvis

Question

Suggest why a vestigial structure, once it has been reduced, may not disappear altogether

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The genes for vestigial hind limbs are still present in the species OR

The vestigial structure is no longer an advantage/disadvantage and are therefore not selected for or against.

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Biochemical composition of most living organisms are remarkably similar

Strengthen the idea of a common ancestor Characteristics that indicate possible common origin of

different organisms include identical DNA structure, similar sequence of genes, identical protein synthesis etc.

Cytochrome C- similar amino acids in cytochrome C of different organisms.

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The study of the distribution of plants and animals across the Earth.

Different but closely related species are found in similar biomes and have similar features adapting to that biome

Probably developed from common ancestral species.

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The distribution of species around the

world suggests that modern forms

evolved from ancestral populations

and spread out (radiated) out into

new environments.

Good examples are found on

islands offshore from large

continental land masses:

Galapagos Islands

Cape Verde Island

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CAN YOU SPOT THE FOSSIL(S) ?

Australopithecus sediba

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THANK YOU