Evidence for Evolution

Biogeography This is the study of the geographical distribution of species, both present-day 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.