The Origin and Evolution of Life

1. The Origin and Evolution of Life

2. The Origin and Evolution of Life • The origin of life and evolution of life are distinct subjects • the origin of life is a unique event with the fact of life as its only extant clue • the evolution of life is an ongoing process that has left behind clues about its processes and products

3. As Pasteur showed, life does not arise spontaneously (today).Figure 3.28

4. The Origin and Evolution of Life • The Origin of Life (Chapter 25) • How did life appear? • speculative research with no direct evidence • assumes the uniformity of physical laws • deduces original conditions from relics • attempts to construct plausible scenarios

5. The Origin and Evolution of Life • The Evolution of Life (Chapters 21-24) • a.k.a. The Origin of Species • Given the fact of life, how did it get this way? • abundant • diverse • filling essentially every niche

6. The Origin and Evolution of Life • “Evolution” is not a thing or a single, well defined process that is superimposed on life • it is a descriptive subject encompassing a diverse set of processes that occurred during the development of life • its discussion is necessarily full of generalizations and approximations

7. The Origin and Evolution of Life • “Evolution” is not a thing or a single, well defined process that is superimposed on life • its study is forensic • as every crime is unique, so the set of processes that represents the evolution of any lineage is unique • evolution is described, not by a set of “laws”, but by a set of profiles

8. The Origin and Evolution of Life • “Evolution” is not a thing or a single, well defined process that is superimposed on life • evolutionary biologists are “profilers”… • “evolution has been observed to occur in this way in the past and can be expected to behave in a similar way in the future…” • the student of evolution does not learn a few laws by which evolution always occurs, but rather the questions to ask to learn the details of specific examples of evolution

9. The Origin and Evolution of Life • Evolution • definitions: • change over time • descent with modification - phenotypic • changes in a population’s gene pool • populations evolve, individuals do not

10. The Origin and Evolution of Life • The history of life on Earth covers an enormous expanse of time about which we know nothing directly • the study of evolution is largely forensic • Evolutionary Biologists use experimentation primarily to test the plausibility of hypotheses that cannot be tested directly

11. The Origin and Evolution of Life • The history of life on Earth is an interdisciplinary field of study • The age of Earth & early conditions - planetary science • The ages of fossils - the ages of rocks that contain them • Ancient conditions - sea level, O2 concentration, continental positions, etc.

12. Horseshoe CrabsFigure 33.16

13. Chambered NautilusFigure 32.26 Chambered Nautilus

14. CoelacanthFigure 34.14

15. Change in Prevalence of Thick Shelled Snails with Time

16. The Origin and Evolution of Life • The forensic clues to the evolution of life are limited and incomplete • fossils from different sites reveal different images • stasis • slow, gradual change • bursts of rapid change

17. The Origin and Evolution of Life • The forensic clues to the evolution of life are limited and incomplete • spotty clues can yield misleading images • gaps can mask rapid changes • migration can mimic rapid change

18. A little philosophy • How did life on Earth begin? • A question of fact • How do you know? • A question of epistemology (the branch of philosophy dealing with the origin & nature of knowledge)

19. A little philosophy • Before a person can know anything, that person must believe something.Augustine • All knowledge and belief rests upon other beliefs that we presuppose or hold without support from arguments or evidence. • unproven and unprovable basic beliefs • e.g the law of non-contradiction • A cannot be both B and non-B at the same time and in the same sense.

20. A little philosophy • Before a person can know anything, that person must believe something.Augustine • an alternative view • Evidentialism: • “It is wrong always, everywhere, and for everyone, to believe anything upon insufficient evidence.”

21. A little philosophy • Before a person can know anything, that person must believe something.Augustine • another alternative view • Scientific Positivism: • “It is wrong to believe in any proposition that is not verified by the scientific method.”

22. A little philosophy • A paradigm is constructed from our basic beliefs • a filter with which to screen incoming propositions without exhaustive evaluation

23. A little philosophy • according to a Theistic paradigm: • certain propositions are rejected outright, regardless of the evidence supporting them or their logical consistency. Rejection is on the basis of fundamental unproven beliefs rather than rational evaluation.

24. A little philosophy • A Naturalistic paradigm: (such as that held by Carl Sagan who stated that the material universe is all there is or was or ever will be.) • according to a Naturalistic paradigm: • certain propositions are rejected outright, regardless of the evidence supporting them or their logical consistency. Rejection is on the basis of fundamental unproven beliefs rather than rational evaluation.

25. Paradigm Blindness • The Anthropic Principle • FACT: • The physical constants of the universe that govern the behavior of time, energy & matter are finely tuned to support life on Earth. • expansion rate of the universe: 1 part in 1060 • gravitational constant: 1 part in 1040 • etc. (~39)

26. Paradigm Blindness • The Anthropic Principle • The physical constants of the universe that govern the behavior of time, energy & matter are finely tuned to support life on Earth. • SAP: “Therefore, God fine-tuned the universe.” • WAP: “Of course they are! If they were not so, we would not be here to measure/calculate them.”

27. Paradigm Blindness • Paradigms • some people “think” with their paradigms “That’s stupid (or ignorant or evil).” • an argument ad hominem • evidence of “paradigm defense” • inhibits a thoughtful attempt to understand or explain

28. A little philosophy • A Challenge • when discussing controversial subjects (such as the origin or evolution of life): • know your paradigm • remember that understanding a competing proposition is not the same as accepting it • own your paradigm. Don’t let your paradigm own you.

29. A little philosophy • modern science operates according to methodological naturalism. • positively: the universe is orderly and operates according to law-like principles that can be described. • negatively: you can’t appeal to the supernatural to explain accessible natural phenomena that you don’t yet understand

30. A little philosophy • modern science operates according to methodological naturalism • some scientists, like some non-scientists, subscribe to philosophical naturalism • “You can’t appeal to the supernatural to explain anything, because it doesn’t exist.” • regardless of the level of commitment, scientific attempts to understand the origin and evolution of life are necessarily naturalistic.

31. A little philosophy • A prior philosophical commitment can lead to the adoption of arguments that lack persuasive power when viewed objectively, but make sense within a certain paradigm.

32. Quiz: Turn In As You LeaveAnswer Anonymously If You Wish 1. How did life on Earth begin? 2. How do you know?