CHAPTER 16 NOTES

EVIDENCE OF EVOLUTION

 

1. FOSSIL RECORD: any evidence of an organism that lived long ago.

·    Darwin believed that the Earth was many millions, not thousands, of years old.

·    By comparing fossils from older rock layers with fossils from younger rock layers, you can see that life on Earth has changed over time.

 

 

 

2. GEOGRAPHIC DISTRIBUTION OF LIVING SPECIES:                                                    

·    Animals living on different continents each descended from different ancestors.

·    However, animals living under similar ecological conditions on those different continents evolve features in common. 

·    These features in common are called analogous structures: structures that are different in basic structure but the same in function or form.

·    Do not show evolutionary relationships but does provide evidence of evolution by natural selection.

 

Example: butterfly’s wing, bat’s wing, bird’s wing and pterosaur’s wing

 

3. HOMOLOGOUS STRUCTURES: structures that are the same in basic structure (because they develop from the same embryonic tissues) but different in form and function.

 

·    Suggest a common ancestor.

·    Show strong evolutionary relationships

 

 

4. VESTIGIAL STRUCTURES: any structure that is so reduced in function or size that they are just vestiges or traces of the original structure.

 

·    The structure may have been used in an ancestor.

·    The structure may be used in another animal alive today.

 

 

 

Example #1: Appendix in humans

Example #2: Small leg bones in pythons

Example #3: Pelvic bone in whales

 

 

5. SIMILARITIES IN EMBRYOS: similar embryos suggest that similar genes are at work in early development.

 

                                                                     

·    Groups of embryonic cells develop in the same order and in similar patterns.

·    The same set of genes control this development.

·    Mutations to the genes that affect this early development are more often fatal than mutation to the genes that affect later development.

·    Suggest a common ancestor.

·    Show strong evolutionary relationships

 

 

 

 

6. BIOCHEMICAL COMPARISONS:
  • The more similar the DNA, the more related the two organisms.
  • The more similar the DNA, the more recently they share a common ancestor.
  • Scientists have begun to compare homologous proteins such a cytochrome c and homologous genes such as the Hox genes.

Molecular clocks: uses mutation rates in DNA to estimate the time that two species have been evolving

independently.

Uses only neutral mutations which have no effect on phenotype.

Neutral mutations tend to accumulate in the DNA in different species at about the same rate.

The more neutral mutations, the longer ago two species shared a common ancestor.