Evidences of Evolution

How old is the Earth? Geological records reveal that Earth is about 4.5 billion years old. Fossils of single cell bacteria have been found from 3.5 billion years ago.

I-Fossils Fossils can be found in a variety of substances and can be made from a variety of objects such as: Ice Amber (solidified tree sap) Tar Shells Bone

Fossils cont’d. Fossils are found in layers of sedimentary rock such as shale The fossils found in lower layers of rock are older than those in layers closest to the top Newest Oldest

II- Comparative Anatomy Parts such as bones and organs are examined and compared between organisms The more similar the structure, the more likely the two share a common ancestor Homologous structures = those with similar structure, but may have different function Example: the bones of the wing of a bat are similar in type and layout to those of our arm, but they are used differently

Homologous Structures

Analogous Structures These structures have similar function, but when examined do NOT have similar structure These do NOT provide evidence for common ancestry Why do whales and sharks both have fins? One is a fish and one is a mammal However they live in the same environment

Vestigial Structures These are structures that no longer have a function in a species Since they are not harmful to survival they are not selected against and continue to be passed on What structures do we have that could be considered vestigial?

III-Comparative Embryology While adults of different species do not resemble each other, the embryos shed light on unexpected common ancestry Early on it is difficult to distinguish the embryos of humans from that of chickens and salamanders! The more stages of development in common, the more closely related the two species are Examine the diagram on the next slide, who is our closest relative?

IV- Comparative Cytology Cyto- sounds like cytoplasm, which is found in cells -ology = study of Cytology therefore is the study of cells The more similar the cell parts between two species, the more closely related they are For example two cells that have chloroplasts and cell walls are more closely related than one with chloroplasts and one without

V- Comparative Biochemistry Biochemistry is the field of science that focuses on chemicals and their reactions in living things If two organisms have similar chemical compounds (such as a particular enzyme) they are closely related DNA is a chemical compound, therefore the more similar the sequence of bases between two species, the more closely related they are

What do these forms of evidence tell us? The more of these items two organisms have in common, the more closely related they are If organisms share structures and substances they are said to have a…. COMMON ANCESTOR!