1. The Nature of Change and Variation
Unit: Evolution Aim: What evidences do we have to show that evolution takes place?
The Nature of Change
and Variation

2. Change in living things over time
What is Evolution?
Change in living things over time

3. Why study evolution?
Evolutionary concepts underpin much of modern biology
- you can’t fully understand current trends in biology if you don’t understand evolution

4. In the early days... 1744-1829 – Jean Baptiste Lamarck
Prior to people believed organisms were fixed- that is they didn’t change
– Jean Baptiste Lamarck
Evolution through the inheritance of acquired characteristics
Traits acquired during an organism’s life could be passed on to their offspring
Giraffes long necks explained by repeated stretching
hypothesis rejected

5. Types
Macroevolution = speciation – the formation of new species. The change in species over time
Microevolution-changes in genes/alleles within a population.

6. Charles Darwin Alfred Wallace
Descent with modification.
The Origin of Species. 1859
Species were not created in their present forms but evolved from an ancestral species.
Natural selection, the
mechanism by which
change occurs (Explanation
of how evolution occurs).

7. Evidence of Change Fossil Record Embryology
Molecular Biology-Amino Acids, Nucleotides, DNA sequencing, mitochondial DNA
Anatomy

8. Fossil Record
Fossils are a major source of information about changes in life during the
distant past
In general, fossils
show that life has
increased in
diversity and complexity over time

9. Fossil Record
Interpretation of the distribution of fossils in the rock initially based on the principle of superposition
- in undisturbed rock layers, older fossils will be found lower in the rock than younger fossils
-radiometric dating confirms this
In general older life forms tend to be less complex
Periods of diversity are interrupted by mass
extinctions – followed by new life forms
Fossil Record is incomplete – estimated only 1 in 10,000 extinct species are represented – Why?

10. Embryology All vertebrate embryos have
Gill slits on sides of the throat
Post anal tail
The fact that organisms without gills, or tails have them as embryos is taken as evidence of a common ancestry with organisms that had both
Which is the fish, rabbit, human, chicken, tortoise?

12. Comparative Anatomy
Similarities in structure between organisms was used
to determine evolutionary relationships

13. Other Proof From Anatomy
Vestigial structures – structures that are greatly reduced with little or no function
- they are thought to be left over from
ancestors
Pelvis and leg bones in snakes
Reduced toe in horse
Appendix in human
Coccyx (tail bone) in humans
Human male nipples

14. Vestigial Structures

15. Comparative Anatomy Analogous Structures
Similar function but different structure -
Insect’s wing, Bird’s wing and Bats wings
– all allow flight, but are structurally different
Eyes of Molluscs and Vertebrates – both allow sight, but are different in structure

16. Comparative Anatomy Homologous Structures
Have a similar structure but different function
The forelimbs of vertebrate animals all have the same structural design, but they have different functions
This similarity of structure shows a common ancestry

18. Molecular Biology
Comparisons of the sequences of amino acids in proteins or nucleotides in DNA
can show the relationships between organisms
- the number of differences in the sequences of amino acids or nucleotides indicates how closely related two organisms are

19. Hemoglobin Comparison
Species AA differences from humans
Gorilla 1
Rhesus Monkey 8
Mouse 27
Chicken 45
Frog

21. Cladogram (family tree) created from a fossil record

22. Bird Evolutionary Tree
Trees/cladograms are also created using comparative DNA sequences.
If the DNA is very similar to each other, it means they share a fairly recent common ancestor.