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Evidences of Evolution

Read Section 8.2 on pp. 332 – 338 of your textbook

There are 5 key evidences for evolution: 1. Fossil record

2. Biogeography

3. Anatomical evidence (homologous structures, vestigial structures)

4. Embryology

5. DNA evidence

1. Fossil record

• Fossils are preserved remains or markings left by organisms that lived in the past.

• Paleontologists (scientists who study fossils) have discovered fossils of many ancestral life forms that link past and present. Fossil evidence supports the hypothesis that whales, which have no hind limbs, evolved from land-dwelling ancestors with four limbs.

Fossil record

Fossil Record

• The oldest fossils are called microfossils, and they are the fossilized remains of single celled organisms. They must be viewed under a microscope.

• Microfossil evidence suggests that life first evolved about 3.5 billion years ago.

• Microfossils are found in ancient rock structures in South Africa and Australia.

• The microfossils form structures called stromolites. Stromolites are produced by microbes (mostly photosynthesizing cyanobacteria) that form microbial films that trap mud. Over time, these layers of microbes and mud form “mats” that build up into a layered rock structure.

Stromolites

Fossil record – see p. 334

1. Fossil record

Provides the following evidence:

• Fossils found in younger rock layers (close to surface) are more similar to species alive today that those fossils found in older, deeper layers of rock

• Fossils appear in chronological order in rock layers. Probable earlier ancestors for a species are found in deeper rock layers, which lie beneath the more recent ancestors.

• Not all organisms that are alive today have ancestors at all layers of the fossil record. Fossil history suggests tat the oldest vertebrates (back-boned animals) are fish. In recent layers of rock, you will find amphibians, reptiles, mammals and birds.

Fish amphibians reptiles mammals

birds

Transitional fossils

These are fossils that fill in gaps in the fossil record. They show intermediary links between ancient and more recent fossils.

Basilosaurus – fits in between

2. Biogeography

• The study of the past and present geographical distribution of organisms.

• It suggests that organisms evolve in one area, then spread out to other regions

• Geographically close environments (e.g. desert and forest in South America) are more likely to be populated with related species than are locations that are geographically separate but environmentally similar (e.g. desert in Africa, desert in Australia).

• E.g. cacti are only found in deserts in North, Central and South America, not in deserts in Africa or Australia

2. Biogeography

• Animals found on islands often closely resemble animals found on the closest continent.

• E.g. Darwin’s Galapagos finches were more similar to finches found in South America than to those found in England

2. Biogeography

• Fossils of the same species can be found on the coastline of neighboring continents.

• The supercontinent Gondwana broke apart about 150 million years ago.

3. Anatomical Evidence

• Homologous structures have similar structure, but may have different functions. For example the forelimbs of vertebrates contain the same set of bones organized in similar ways.

3. Anatomical Evidence-Homologous

structures All mammals have an almost identical

number and arrangement of bones. Bat Human

Analogous Structures

• Analogous structures evolve in organisms that live in similar environments that do not share a common ancestor.

For example the wing of a bird and the wing of a butterfly have a common function but very different internal anatomy.

3. Anatomical – Vestigal Structures

• These are structures that serve no useful function in a living organism.

• Examples:

• digits in dogs and horses.

• Wings in beetles.

• Ear muscles in humans

• Hip bones in whales

• Human Appendix

4. Anatomical - Embryology

• The study of embryos has been used to determine the evolutionary relationships between animals.

• Similarities in the embryos of fish, birds, and mammals provide evidence of evolution from a common ancestory.

5. Molecular Evidence (DNA)

• Scientists can determine how closely related organisms are by comparing the sequence of DNA in genes, and the sequence of amino acids in proteins.

• The DNA and RNA in all living organisms share the same four base code.

• Adenine Thymine(Uracil)

• Cytosine Guanine

Molecular Evidence