1. Evolution:
Supporting Evidence

2. The following items demonstrate descent with modification, as well as common ancestry. (Darwin’s principle of common descent)

3. I -Fossil Evidence (descent with modifications)
Horse fossils indicate changes in size,
as well as the transition from toes to hooves.

4. I - Fossil Evidence: Continued
These mollusk
fossils show
the development
of torsion, the
twisting of
their shells.

5. II -Homologous Structures are fundamentally similar in their makeup, position and development, but are adapted to different functions.
Animal Forelimbs:

7. The Galapagos finch beaks are said to be homologous
The Galapagos finch beaks are said to be homologous. They originated in a common ancestor and have adapted to various environments.

8. Homologous v. Analogous
What’s the Difference?
Homologous structures are features that originated in a shared ancestor. They have different mature forms, but develop from the same embryonic tissue.
They are inherited from a common ancestor.

9. Analogous Structures have features that have identical functions, and look somewhat alike, but they may be different in internal anatomy.
The evolved independently after their point of common ancestry, so they were not inherited from a common ancestor.
A bird’s wing and a moth’s wing are analogous. They allow the animals to fly, but
They have greatly different development and internal structure.

10. Moth Wing Structure

12. Catoblepia berecynthia

13. Bird Wing Anatomy
Bones & Feathers

14. Also Analogous: Insect & horse legs

15. III -Vestigial Structures which may have been functional in an ancestor, are functionless and underdeveloped in later generations
Human tailbone
(coccyx)
Human Appendix

16. III - Vestigial Structures: Structures that are vestigial in one organism, may be functional in others.
Nictitating membrane
Ear muscles

17. III - Vestigial Structures (continued):
Limb bones
in snakes
Pelvic
bones
in whales

18. III – Vestigial Structures: Continued
Erector pili muscles
which cause “goose bumps”
in humans
Human baby
born with fleshy
tail

19. Does the tail
really exist?

20. Baby girl
born in a hospital
in Chile

21. IV -Embryological Similarities
Various embryos in early stages show
evidence of gills slits and tails.

22. V - Biochemical Evidence
All organisms have DNA
(& RNA)
All organisms have ATP
Similarities in cell respiration
enzymes

23. V- Biochemical Evidence (Continued)
All organisms have cytochrome c
in the electron transport chain
(The difference in A.A.s is proportional to the length of time that has passed since the two shared a common ancestor.)

24. VI – Homeotic Genes
Homeotic genes (Hox genes): regulatory genes that determine where certain anatomical structures, such as appendages will develop in an embryo. “They seem to be master genes of development that determine the overall body organization.”
Common ancestry is demonstrated because animals share many of these Hox genes, which may control the development of similar regions.

26. In Summary
Scientists have continued to observe examples of common ancestry and descent with modifications
since Darwin observed finches on the Galapagos Islands so many years ago.