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Evidence for Evolution Biogeography • This is the study of the geographical distribution of species, both presentday and extinct. • Geologically separate areas tend to be inhabited by organisms that are ecologically similar: on islands, the organisms tend to be unique. – E.g. the development of marsupials in Australia but not elsewhere. The Fossil Record • Any non-living object obtained from the ground that indicates the former presence of a living thing is a fossil. • Fossils are the remains of living things – bones, shells, or other parts resistant to decay – or their traces such as footprints or burrows that have been preserved in the rock. The Fossil Record • Where rock strata can be aged, the succession of fossils in the layers show that the most primitive forms of life are the oldest strata. • The progression of the fossils follows the evolution of life as we know it from other sources. Formation of Fossils • Most fossils occur in sedimentary rock. • Sediments in the sea gradually cover the dead body on the sea floor and petrify it. The Process • A dead animal falls to the sea floor. • Sediment covers the skeleton; other bodies fall to the new sea floor. • Time passes; layers of different rocks form. • Movement of the Earth’s crust folds the rock layers. • Erosion of the rock means that fossils can be seen. Comparative Anatomy • Homologous Structures – these show similar characteristics resulting from common ancestry. – E.g. pentadactyl limbs Comparative Anatomy • Analogous Structures - these have the same function but different ancestry. – E.g. birds and insects have wings. Comparative Anatomy • Vestigial Organs – these are organs that have become reduced or have lost their function. – E.g. the tail bones in humans and the wing bones in a kiwi. Comparative Embryology • The early embryonic stages of all vertebrates are very similar, even though the adults are all very different. Molecular Biology • Species which are close in evolutionary terms have only small differences in their DNA and proteins. • Even organisms from different taxonomic groups have some common proteins. – All living things have DNA so they must have had a common ancestor.