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. Fossil record2.Geographical distribution of living species3.Anatomy4. 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.