Section 8.2 – Evidences of Evolution

There are 5 key evidences for evolution:1.

2.

3.

4.

5.

1. Fossils are ______________________ or _______________ left by organisms that lived in the past.

_________________________ (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.

The fossil record provides the following evidence:

• Fossils found in younger rock layers (____________________) 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 that the oldest vertebrates (back-boned animals) are ____________. In recent layers of rock, you will find amphibians, reptiles, mammals and birds.

• The oldest fossils are called _______________________, and they are the fossilized remains of ________________ 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 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.

Transitional fossils - These are fossils that fill in gaps in the fossil record. They show intermediary links between ancient and more recent fossils. Their existence is often predicted to link existing fossils. When they are found, they help support the theories proposed about how a species evolved.

2. Biogeography – The study of the past and present _____________________________________ 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

• 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 (Ecuador) than to those found in England

Some fossils found in deep soil layers in continents that were once connected geographically (Pangaea ) show similarities, even though animals from these areas may no longer show similarities.

3. Anatomical Evidencesa. Vestigial Structures are remnants of structures that may have had important functions

in an ancestral species. Vestigial structures are often reduced in size. For example: Hip bones in whales

b. Homologous structures are structures that are similar because they were inherited from

a _____________________________. These structures may have evolved to have different ____________________.

Human appendix

ANALOGOUS STRUCTURES – these are NOT evidences of evolution.

• An analogous structure is a structure that has a similar _____________________ in contemporary species, but has evolved through different pathway.

• Structurally they are often ____________________________.

Example: bees wings and bird wings

4. Embryology – • In the development of an embryo, ______________traits appear before the more

__________________ traits.

• Embryos of different species are more alike than the adults, and they change progressively during their embryonic growth to look less and less alike.

• Vertebrate embryos show many similarities, for which the most reasonable explanation is their __________________________________.

Example: The _____________________ in the mammalian embryo are similar to those of a fish embryo at a comparable stage of development. They change into structures quite different from those in the fish. All the _________________________ close and disappear except the one that forms the Eustachian tube, which connects the pharynx at the back of the mouth to the middle ear.

The obvious question is why should there be a stage in the mammalian embryo where gills are present, even though they form quite different structures in an adult mammal?

The answer is that the mammals are descended from ______________________ and that in the course of evolution ____________________ have occurred in its development.

• The similarities which still persist in the embryonic development of fish and mammals indicate a similarity in their ______________________ due to their _______________________________.

• Embryos still carry the clues to their common ancestry.

5. Molecular Evidence

What molecule serves as the blueprint of life?

What molecules are encoded for by DNA?

How do we compare organisms from a molecular point of view?