Evidence of Evolution Evidence of Evolution Darwin argued

Evidence of Evolution

Evidence of Evolution • Darwin argued that living things have been evolving on Earth for millions of years. • Evidence supporting his theory could be found: 1. 2. 3. 4. Fossil record Geographical distribution of living species Anatomy Similarity in early development (embryology)

1. The Fossil Record • Darwin saw fossils as a record of the history of life on Earth. • Darwin proposed: – Earth was millions, rather than thousands, of years old – Countless species had come into being, lived for a time, and then vanished.

2. Geographic distribution of Living Species • Species now living on different continents had each descended from different ancestors. • Some animals on each continent were living under similar ecological conditions so they were exposed to similar pressures of natural selection.

Similar, But Unrelated Species As a result, Darwin concluded that because of these similar selection pressures, different animals ended up evolving certain features in common!

3. Anatomy • Darwin noticed similarities among the body parts of various animal and plants. • There are three different types of structures to help support Darwin's Theory of Evolution. 1. Homologous Structures 2. Analogous Structures 3. Vestigial Structures

Homologous Structures • Homologous Structures – Structures that are similar and have originated from a common ancestor. – May look different on the outside, but have similar structure inside. – Indicates that organisms may have shared a recent common ancestor.

Homologous Structures cont’d. • The limbs of different organisms serve different functions, but have the same bone structure inside.

Analogous Structures • Analogous Structures – Structures that serve identical functions, but have different internal anatomy. – Ex: wings of birds and insects • Both allow organisms to fly, but have different development and structure. – Shows a more distant relationship than homologous structures.

Identify the following structures as analogy or homologous. Be able to defend your answer!

Vestigial Structures • Vestigial – structures that were useful in ancestors but are no longer used by modern organisms • Shows relationship between organisms with vestigial structure and those with a working version. • Ex: humans have tailbones homologous to tails of other animals

Vestigial Structures cont’d. • Some organisms have genes that are conserved. – Genes that have remained unchanged, but may be “turned off”. • Ex: whales have genes for hind legs • Can give clues about early development of a species. – Ex: whales may have descended from an ancestor who lived on land

4. Embryology • Embryology – study of early development • Many organisms share similarities within the early stages of development. • The same groups of embryonic cells develop in the same order and in similar patterns to produce the tissues and organs of all vertebrates. • These common cells and tissues, growing in similar ways to produce the homologous structures! • Can indicate a common ancestry among different species.

Embryology cont’d.

Similarities in Macromolecules • Similarities within DNA, RNA and proteins of different species – Genetic code is universal – all living things share the same code – Closely related species have very similar gene sequences and protein sequences. • Ex: hemoglobin in humans and gorillas differs by only 1 amino acid – Can confirm ideas suggested by anatomy and embryology.