1. The Scientific Evidence for Evolution

2. Evidence of Evolution SB5
Students will evaluate the role of natural selection in the development of the theory of evolution.
Explain how fossil and biochemical evidence support the theory.
Relate natural selection to changes in organisms.

3. Snapshot of the past that illustrates evolutionary change.
Fossil Record
Snapshot of the past that illustrates evolutionary change.
Fossil record is progressive (ancient to modern form)
Incomplete

4. Petrification of softer parts Replaced by minerals Whole animals
Fossil Record
Examples of Fossils:
Bones, teeth, shells
Petrification of softer parts
Replaced by minerals
Whole animals
Glaciers, amber

5. Fossil Evidence A fossil is any trace of a species that once lived.
From Campbell & Reece, Essential Biology, 2001

6. A dinosaur?
This dinosaur fossil was found by a British school girl. Scientists thought it was a small, common dinosaur. It has a long bony tail, a lizard like pelvis and a mouth full of teeth. But someone looked more closely…

7. Look carefully – those are feathers surrounding the skeleton
Look carefully – those are feathers surrounding the skeleton. This creature had the head, pelvis and tail of a dinosaur, but bird like wings and feathers.
Fossils that show a mix of characteristics - Transitional Fossils

8. Fossils shows how species have changed over a long period of time
Fossil Record
Fossils shows how species have changed over a long period of time

9. Comparative Anatomy

10. Analogous structures Different structures (different ancestors)
Same function
Similar environments
Shows the evolutionary link between related species

11. Analogous

12. Homologous Structures
Same structures
Different functions
Different environments
Shows a common ancestor between organisms.

13. Homologous Structures
Forearm of vertebrates
Human, cat, whale, bat
Derived from same common ancestor

14. Embryonic Development
All vertebrates look similar in early development
All have gill slits and a tail (even humans)
Gill slits are skin folds in early developing organisms
Reinforces the fossil records

15. Embryonic Development
Shows a link to a common ancestor

16. Embryological Evidence

17. Embryological Evidence
Vertebrate embryos go through a set of stages that match the progression in the fossil record.

18. How do the embryos develop into different organisms?

19. It seems that all vertebrates have genes to make a tail, and four limbs.
There are other genes that turn off the first gene.
So, for example, dolphin embryos make hind limbs, but then that gene is turned off and the embryo reabsorbs the hind limbs.

20. What would happen if that first gene didn’t get turned off?

21. Sometimes old genes are expressed
This dolphin was caught off the coast of Japan. It has FOUR flippers – two forelimbs, and two hind limbs. The gene for the hind limb was expressed.

22. Human Baby with a Tail
There are over 100 medically recorded cases of human babies born with tails.
About 30% of these are considered to be “pseudo-tails” –The rest are “true tails”
As an example, this newborn could extend or contract the tail because it had muscles in it, although it had no bones.

23. Vestigial Structures Structures with no apparent purpose today
Pelvic bones of whales
Human tail bone
Human appendix
Emu wing
Shows common ancestory

24. Vestigial Structures
Pelvic bones in pythons are unused remnants from their common ancestor shared with lizards
We would not expect to see these structures if snakes had an origin separate from other vertebrate animals.
Blind salamanders have eyes with retinas and lenses, yet the eyelids grow over the eye, sealing them from outside light

25. Vestigial Structures
Flightless Cormorant Wings: Cormoront lives on Galapagos Islands, & has wings too small for flight
Legless Skinks a type of lizard. In some species the legs have become vestigial. (so reduced that they no longer function)

26. Human Vestigial Structures
Humans have > 100 vestigial structures.
90% develop wisdom teeth (molars used for chewing & grinding plant material) which usually don’t erupt from gums, can be malformed and cause pain.
Tailbone (Coccyx) fused vertebrae that in other vertebrates are tails. It serves no purpose.
Ear muscles used in other vertebrates for twitching
Appendix part of digestive tract used to digest tough plant material is so reduced in humans that it is dysfunctional

27. Humans don't have fur, right?
At least, most of us don’t.
We have the gene for fur or hair over most of our bodies.
In almost all people, this gene is turned off.
In some people however, this gene is expressed.

28. Biochemical and Genetic
Biochemical: Similarities between organisms’ protein structures & enzymes
Genetic Analysis: Similarities between organisms’ DNA & genes
Shows us how closely related organisms are
Example – how similar is our DNA?
Humans = 99.9%
Chimpanzees = 96-99%
Yeast = 70%

29. Fossil Record Anatomical Molecular Biogeography Embryological
Embryological development matches the progression of fossils in the fossil record
Vertebrates not only repeat the development of ancestral vertebrate but they have similar bone structure and unused remnants of their structures
Anatomical
Embryological
Mutations exhibited in bacteria provide concrete evidence for the changes that lead to the branching of species observed in the fossil record
Present & past distribution of continents explains the distribution of fossils
Amino acid sequences are more similar in species with more similar bone structures.
Biogeography
Molecular

31. Evolution Populations evolve not
Remember: Evolution doesn’t give organisms what they need.