Evidence for Evidence for EvolutionEvolution

BiogeographyBiogeography

• 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 RecordThe 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 RecordThe 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 FossilsFormation 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 ProcessThe 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 AnatomyComparative Anatomy

• Homologous Structures – these show similar characteristics resulting from common ancestry.– E.g. pentadactyl limbs

Comparative AnatomyComparative Anatomy

• Analogous Structures - these have the same function but different ancestry.– E.g. birds and insects have wings.

Comparative AnatomyComparative 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 Comparative EmbryologyEmbryology

• The early embryonic stages of all vertebrates are very similar, even though the adults are all very different.

Molecular BiologyMolecular 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.