Evolution in Humans and the Thoughts of Major Evolutionary Scientists

1. Sarim Baig Evolution in Humans and the Thoughts of Major Evolutionary Scientists

2. Evidence for Human Evolution • Homology • Vestigial Organs • Appendix, Tailbone, and others • Paleoanthropology • Similarities between humans and others in the “Homo” genus, as well as earlier species.

3. Homology • Mammalian Forelimbs • Most often cited example of homology • Humans differ greatly from other mammals such as bats and whales yet have almost the exact same bone structures in the forelimbs. • Single bone attached to two bones which are then attached to multiple bones. • Each of these structures was slightly modified in order for the organism to adapt to its surroundings. • Same bone structure allows species to fly, swim, run, etc.

4. Homologous Structures

5. Vestigiality • Structures whose physiological roles in the organism have either been diminished or have disappeared altogether. • Human tailbone: • Other organisms use the tailbone as a means for balance, communication, and even movement. • Other organisms such as dogs have a much larger and more pronounced tailbone than humans. • Human tailbone is a small “hook” at the end of the vertebral column and has no function in movement and/or balance.

6. Human Appendix • The human appendix is a “worm-like” structure found in the digestive system at the end of the “caecum”. • Gradually shrinks in humans as we age. • The appendix can be removed surgically without any major side effects. • Other mammalian organisms such as rabbits also have an appendix, yet their appendix has a defined function.

7. The function of the appendix • Appendix and caecum play a vital role in the digestion of cellulose in herbivorous animals. • In humans, enzymes that are used to digest cellulose are found in low quantities in the caecum and are mostly absent in the appendix. • In rabbits, the appendix plays a major role in its immune system • Half of its lymphoid tissue found in appendix • Majority of human lymphoid tissue is found in the small and large intestines.

8. Vestigial Organs: Appendix Figure: Rabbit Appendix (Left), Fetal Human (Middle), Adult Human (Right)

9. Other Vestigial Structures in Humans • Wisdom Teeth? • Many individuals never have their wisdom teeth come in. • Many are often impacted and need to be removed. • Generally not used for biting and/or chewing. • Genes for Vitamin C- Ascorbate • The human genome has the majority of the genes needed to produce vitamin C internally, yet humans are incapable of doing this. • Evolved this trait because early humans consumed a lot of vitamin C in their everyday diet.

10. Paleoanthropology • Study of early hominids and how their biological and cultural characteristics are related to modern-day humans. • Majority of the evidence in this field came from studying the fossil record. • Earliest definitive hominids were of the Australopithecus group, which lived around 4 million years ago. • Two major trends are seen in the history of hominids. • Evolution of bipedalism • Greater intellectual capacity

11. Bipedalism • The ability to walk on two legs is directly related to the length of the arms relative to the legs. • Species with longer arms and shorter legs are much more likely to be quadropeds. • Species with shorter arms and longer legs are more likely to be bipedals. • Humerus to Femur ratio • Chimps: ~ 1 : 1 • A. afarensis (Lucy): ~ 0.85 : 1 • Humans: ~ 0.72 : 1

12. Intellectual Ability • The overall intellectual ability of mammalian species has been attributed by some to be directly related to the size of the organism’s brain. • Brain sizes in hominids have gradually increased over time. • Led to the development of tools in later hominids and other innovations (Fire, agriculture).

13. Intellectual Ability Continued • A. afarensis: ~ 400 cc • Lived 4 m.y.a • Approximately the same size as chimps and other apes. • A. boisei: ~ 530 cc • Lived 2 m.y.a • Homo erectus: ~ 900 cc • Lived up until 300,000 years ago • Homo neanderthalensis: ~ 1500 cc • Lived up until 30,000 years ago • Homo sapiens: ~ 1350 cc

14. Trends in Hominid Brain Size Chimpanzee Australopithecus afarensis Australopithecus boisei Homo erectus Homo neanderthalensis Homo sapiens

15. Differences between Early Hominids and Late Hominids

16. Charles Darwin • Witnessed the controversy that followed the publication of his paper and Wallace’s in 1858. • Reluctant to mention anything about evolution in humans in the Origin of Species (1859). • Waited twelve years before making any publication dealing with the issue of human evolution. • Published The Descent of Man after a number of other scientists had already brought the topic into the public eye.

17. The Descent of Man (1871) • Cites homologous structures, vestigial organs, and comparative embryology as evidence that humans evolved from earlier species. • “…that man is descended from some lowly organized form, will, I regret to think, be highly distasteful to many. But there can hardly be a doubt that we are descended from barbarians.”

18. Alfred Russel Wallace • Human evolution was a result of two forces, natural selection and the work of a spiritual being. • Natural selection could not alone account for the “vast superiority of man over its nearest allies.” • “The brain in savage and prehistoric man was in advance of his needs”

19. Thomas Henry Huxley (1825-1895) • “Darwin’s Bulldog” • First to publish on evolution in humans after reading Darwin’s Origin of Species • Evidence on Man’s Place in Nature (1863) • Much of Huxley’s work dealt with the similarities between humans and apes.

20. Huxley-Wilberforce Debate (1860) • Oxford University • Archbishop Wilberforce: known as a skilled debator • Huxley: a relative unknown in the scientific community. • Expected to be a defeat of Huxley and of Darwin’s ideas.

21. Results of Debate and Its Impact • By most accounts, Huxley soundly defeated Wilberforce in the debate. • Wilberforce is said to have asked Huxley which side of his family descended from apes. • Huxley response was that he would rather be descended from apes than from a man afraid to face the truth. • Huxley’s victory made believers out of many individuals in the public who had previously attacked evolution.

22. References http://herc.berkeley.edu/middle_awash/what_is_paleoanth.php. Accessed Nov. 18, 2008. http://www.evoled.org/lessons/human.htm#overview. Accessed Nov. 18, 2008. http://cogweb.ucla.edu/ep/Paleoanthropology.html. Accessed Oct. 27, 2008. http://www.nasw.org/users/karin/globe1.html. Accessed Nov. 22, 2008. http://www.talkorigins.org/faqs/vestiges/appendix.html. Accessed Oct. 27, 2008. http://www.fordham.edu/halsall/mod/1871darwin.html. Accessed Oct. 31, 2008.

23. References Continued Wallace, Alfred Russel. Man and Natural Selection (S173: 1870). The Alfred Russel Wallace Page. Accessed Oct. 31, 2008. Wallace, Alfred Russel. Darwin’s ‘The Descent of Man and Selection in Relation to Sex’ (S186:1871) The Alfred Russel Wallace Page. Accessed Oct. 31, 2008. http://www.ucmp.berkeley.edu/history/thuxley.html. Accessed Oct. 31, 2008. http://cas.bellarmine.edu/tietjen/Ec&Ev_Distance_learning/Evidence/evidence_main.htm.Accessed Nov. 26, 2008. http://www.holyconservancy.org/images/history/1860ad/thomas-h-huxley.gif.Accessed Nov. 26, 2008.