Evidence for Evolution Biogeography This is the study

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.