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Explore how evolution occurs and its evidence, from fossil records and comparative anatomy to molecular biology and DNA sequencing. Understand the concept of evolution through examples like vestigial structures and homologous structures. Learn how comparative DNA sequences reveal evolutionary relationships.
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Unit: EvolutionAim: What evidences do we have to show that evolution takes place? The Nature of Change and Variation
What is Evolution? • Change in living things over time
Why study evolution? • Evolutionary concepts underpin much of modern biology - you can’t fully understand current trends in biology if you don’t understand evolution
In the early days... • Prior to 1760 -people believed organisms were fixed- that is they didn’t change • 1744-1829 – Jean Baptiste Lamarck • Evolution through the inheritance of acquired characteristics • Traits acquired during an organism’s life could be passed on to their offspring • Giraffes long necks explained by repeated stretching • hypothesis rejected
Types • Macroevolution = speciation – the formation of new species. The change in species over time • Microevolution-changes in genes/alleles within a population.
Charles DarwinAlfred Wallace • Descent with modification. • The Origin of Species. 1859 • Species were not created in their present forms but evolved from an ancestral species. • Natural selection, the mechanism by which change occurs (Explanation of how evolution occurs).
Evidence of Change • Fossil Record • Embryology • Molecular Biology-Amino Acids, Nucleotides, DNA sequencing, mitochondial DNA • Anatomy
Fossil Record • Fossils are a major source of information about changes in life during the distant past • In general, fossils show that life has increased in diversity and complexity over time
Fossil Record • Interpretation of the distribution of fossils in the rock initially based on the principle of superposition - in undisturbed rock layers, older fossils will be found lower in the rock than younger fossils -radiometric dating confirms this • In general older life forms tend to be less complex • Periods of diversity are interrupted by mass extinctions – followed by new life forms • Fossil Record is incomplete – estimated only 1 in 10,000 extinct species are represented – Why?
Embryology • All vertebrate embryos have • Gill slits on sides of the throat • Post anal tail • The fact that organisms without gills, or tails have them as embryos is taken as evidence of a common ancestry with organisms that had both • Which is the fish, rabbit, human, chicken, tortoise?
Comparative Anatomy • Similarities in structure between organisms was used to determine evolutionary relationships
Other Proof From Anatomy • Vestigial structures – structures that are greatly reduced with little or no function - they are thought to be left over from ancestors • Pelvis and leg bones in snakes • Reduced toe in horse • Appendix in human • Coccyx (tail bone) in humans • Human male nipples
Comparative Anatomy • Analogous Structures • Similar function but different structure - • Insect’s wing, Bird’s wing and Bats wings – all allow flight, but are structurally different • Eyes of Molluscs and Vertebrates – both allow sight, but are different in structure
Comparative Anatomy • Homologous Structures • Have a similar structure but different function • The forelimbs of vertebrate animals all have the same structural design, but they have different functions • This similarity of structure shows a common ancestry
Molecular Biology Comparisons of the sequences of amino acids in proteins or nucleotides in DNA can show the relationships between organisms - the number of differences in the sequences of amino acids or nucleotides indicates how closely related two organisms are
Hemoglobin Comparison Species AA differences from humans Gorilla 1 Rhesus Monkey 8 Mouse 27 Chicken 45 Frog 67
Bird Evolutionary Tree Trees/cladograms are also created using comparative DNA sequences. If the DNA is very similar to each other, it means they share a fairly recent common ancestor.