evidences of organisms changing over timewhs.rocklinusd.org/subsites/biology/documents/biology/ls 4...

Evidences of organisms changing over time

Fossils• Fossil = any remnant of prior life on earth

(bone, tooth, imprint, etc.) • Found in sedimentary rock, ice or tar! • Only 0.01% of all species can be found in

fossil record!!! • What it tells us:

– Organisms existed before but may not now

Determining Age of Fossils

• Relative Age/Dating = based on location in rock relative to other fossils. – Law of Superposition – new

rock on top, old rock on bottom!

• Absolute Age/Dating = specific age using radioactive ½ life of atoms.

Molecular Biology – Comparing Macromolecules

• DNA – nucleotide sequences are compared

• Proteins – amino acid sequences are compared

• What it tells us: – The more closely related

organisms are, the more similar their DNA/protein sequences are

• They must share a common ancestor!

Comparative Anatomy• Homologous Structures

• Similar structure, Different Function

• What it tells us: – These organisms share a

common ancestor

• Analogous Structure • Different structure,

same function • What it tells us: – Different organisms can

adapt to the environment in similar ways

Comparative Anatomy – Vestigial Structures

• Vestigial Structure • seem to have no

useful function, but has a function in a similar or ancestral organism

• What it tells us: – Organisms share a

common ancestor

Comparative Embryology

• In early developmental stages, related organisms have very similar embryos

• What it tells us: – These organisms have

very similar genes – Organisms share a

common ancestor

Biogeography• The geographic

distribution of species

• What it tells us: – Organisms can

migrate from a place of origin and evolve into new species.