1. Change is constant… Donna May D. Papa College of Science University of Santo Tomas Chapter 6

3. Pre-Darwinian Evolutionary Ideas  Before 18th century - origin of species was not scientific – “Creation Event”  Irreversible change & mythology  Xenophanes, Empedocles and Aristotle developed early ideas about evolution  Fossils were recognized as former life destroyed by natural catastrophe  Archbishop Ussher calculated 4004 bc as date of life’s creation   Louis Buffon (1707-1788) – stressed environmental influences modified animal types

4.  Jean Baptiste de Lamarck offered first complete explanation of evolution (1809)  argued that fossils were remains of extinct animals  mechanism was inheritance of acquired characteristics – transform to produce evolution  Lamarck’s concept is transformational; individuals transform their own traits to evolve  In contrast, Darwin’s theory is variational or due to differential survival among offspring

5.  Principle of Uniformitarianism  two important principles of Uniformitarianism : 1)Laws of physics and chemistry remain the same throughout earth’s history 2)Past geological events occurred by natural processes similar to those observed today  Natural forces acting over long periods could explain formation of fossil-bearing rocks  Geological changes are natural and without direction; both concepts made marks on Darwin’s theory

6. Darwinian Evolutionary Theory: The Evidence   Perpetual Change   Common Descent   Multiplication of species   Gradualism   Natural Selection

7. perpetual change   Species are not fixed, but are often changing (commonly at different rates)   Through the generations, most common forms change, as shown in the fossil record   Fossil - remnant of past life

8. Geological Time Sedimentary Rock Layers  Law of stratigraphy dates oldest layers at the bottom and youngest at the top  Time is divided into eons, eras, periods and epochs (See inside back cover of your books) Evolutionary Trends  Fossil record allows observation of evolutionary change over broad periods of time  Animal species arise and become repeatedly extinct.  Animal survival = 1–10 million years

9. Horse Evolution Shows Clear Trend  From Eocene to Recent periods, genera and species of horses were replaced  Earlier horses - smaller sized and fewer grinding teeth, and more toes  Reduction in toes and increase in size and numbers of grinding teeth correlate with environmental changes

10. Common descent   All forms of life had a common ancestor. Phylogeny – Evolution produces a branching structure and the form, this takes is called a phylogeny

11. Multiplication of species   New species form by splitting and transforming older species   Typically the result of isolation or separation, and based primarily upon reproductive isolation

12. Gradualism   Evolution is a gradual and slow process (by human standards) and large, rapid changes are usually not common in the evolution on a group of organism   Most large changes over time occur through a series of small changes   Large changes tend to be harmful for organisms, although not always

13. Natural Selection Five Observations forming Natural Selection 1.Organisms have a great potential to reproduce

14. 2. Natural populations normally remain constant in size, with small fluctuations

15. 3. Natural resources are limited.   Therefore, a continuing struggle for existence occurs among members of a population

16. 4. All organisms show variation

17. 5. Variation is heritable.   Differential survival and reproduction occur among varying individuals in a population, and over many generations, generates new adaptations and new species.

18. Evidence for Perpetual Change   Seen in the fossil record   Fossils are deposited in stratified layers   Dating possible based on position in the rock   Fossils tend to illustrate trends in characteristic change Ex. Evolution of horses

19. Evidence for common descent   Homology – different adaptations of the same structure from a shared ancestor   Used to form phylogenies based on shared characteristics   Used in ontogeny, or the history of development.   “ontogeny ( history of development of an organism throughout its lifetime ) recapitulates “phylogeny” Comparison of gill arches of Different embryos. All shown Separated from the yolk sac. Note similarity of embryos.

20. Evidence for Common Descent Homologous structures   Arm of a human   Arm of a cat   Wing of a bat   Fin of a whale   Leg of a horse

21. Multiplication of Species   Ancestral species speciate into diverse forms through isolation   End result can be multiple species.

22. How new species arise Allopatric speciation   Speciation due to a geographic barrier - Separated by an ocean, mountain range or a road Sympatric speciation   Speciation in the same place without separation

23. Classic Example – Darwin’s finches   Adaptive radiation – production of many ecological species from a common ancestral stock.

24. gradualism   A theory of some debate today   Fossil record does not show perfect intergrades from form to form   Sporting mutations can cause dramatic changes that may be important to evolution

29. Disturbances to Equilibrium   Random Genetic Drift   Nonrandom Mating   Recurring Mutation   Migration   Natural Selection

31. Nonrandom mating   Positive assortative mating – Individuals selecting a particular genotype to mate with   Inbreeding – mating between close relatives