Evidence of Evolution

Fossils, Comparative Biochemistry, Fossil Dating

Define Evolution

The gradual change in characteristics of a species over time

Define a trace fossil.

The preserved remains of a species not the organism itself.

Define a half life

The time taken for a radioactive isotope to decay by half its orgigional amount.

Define a fossile

Preserved traces left by an organism, which can show trends in the changing of characterisitics and thus evolution.

Conditions for fossil formation

• Low oxygen

• High pH—→ Alkaline/basic environment

• Quick burial

• Lack of moisture

• little disturbance

Problems with the fossil record

Required conditions may not be met; thus, fossilisation is rare.

not a species have been preserved or found.

Some fossils have been destroyed (natural disasters/human activities).

Comparative Genomics

The comparison of the DNA of different species. Species with relatively similar DNA will have a recent common ancestor.

Endogenous Retrovirus

Viral sequences found in organisms’ non-coding DNA, located in the same place on the chromosome in every cell of the body.

Comparison of the amount and placing of ERV can provide evidence of a common ancestor.

Endogenous meaning

A viral sequence found in gametes is thus inherited by subsequent generations generations.

Mitocondrial DNA

Circular DNA is found in the mitochondria and is passed down from the mother.

Relatively short with only 37 genes, thus increased rate of mutations.

This high rate of mutations means the DNA composition is slowing diverging from mtDNA of the original female ancestor.

—→ The number of mutations suggests the closeness in relation to common ancestors.

—→ Similarities in mutations suggest a relationship with that species.

Protien sequences

Based on Ubiquitous proteins, found in all forms of life.

The amino acid sequences of these proteins are remarkably similar across vastly different species, indicating a common ancestor from which these proteins originated. 

Example of Ubiquitous proteins

Cytochrome C—production of cellular energy

the same in humans, chimpanzees, gorillars and others

Phylogenetic tree

Shows the evolutionary relationship between species stemming from the same common ancestor

Absolute Dating

The actual age of a specimen

Potassium-argon dating

Based of the decay of radioactive potassium-40—→ calcium-40 and argon-40

and the amount of argon trapped in a rock can indicate its age

Limitations of potassium-argon dating

It is primarily used for dating volcanic rocks and minerals. 

Rocks must be older that 100 000 years old.

Carbon -14 dating

Based on the decay of radioactive carbon-14 → nitrogen

Once an organism dies,

• The carbon-14 decays and is no longer replaced.

• Carbon 12, a stable isotope, does not decay.

  Thus, the ratio of carbon-14 to carbon-12 shows the age of the specimen.

Limitations to Carbon dating

Fossils must be less than 60 000 yrs. old

The amount of carbon -14 in the atmosphere can vary

What is Carbon -14 half life

5730

Relative dating

The ages of a specimen is estimate in relation to another fossil.

Florine dating

when a specimen is buried in an area surrounded by groundwater that contains fluoride.

—> the longer the specimine is left the more floride will be absorbed

When 2 fossils in simmilar areas are compared, the one with more floride will be older.

Stratigraphy

Based on the idea that layers/strata of sedimentary rock on top are younger than those below. (Law of superposition)

• These fossils closer to the surface are younger than those further away.

Correlations of Rock Strata

• rocks with same fossils are same age

Stratigraphy limitations

Distortions can occur

things may have been buried.

only provides relitive age

Index fossils

The same fossils are widely spread around the world, originating from the same short period of time.

Types of Comparative Anatomy

Embryology

Homologous structures

Vestigial structures

Embryology

Comparing early changes in development

Similarities in early development indicate a common ancestor.

Homologous structures

Structures similar in structure but different in function.

This indicates a common structure.

Example: forelimbs

Vestigial structure

Structures changed during evolution and have little to no more function.

Indicates the degree of difference from the common ancestor.

Changes in skull

Brain size → increased (larger cranial capacity).

Forehead → higher and more vertical (less sloping).

Brow ridges → reduced.

Face → flatter, reduced prognathism (jaw sticks out less).

Teeth → smaller canines, more even tooth size.

Diastema (gap for canines) → present in apes, absent in hominins.

Jaw/Chin → jaws less robust, chin develops in modern humans.

Foramen magnum → moved underneath skull (shows upright posture).