Evolution and Creationism - Reading

Chapter 6: Evolution and Creationism

Outline

  • Creationism

  • Some Creationist Arguments

  • Darwin's Two-Part Theory

  • Natural Selection

  • Speciation

  • The Tree of Life

  • The Principle of the Common Cause

  • Arbitrary Similarities among Organisms

  • Useful Similarities among Organisms

  • Irreducible Complexity

  • Is Creationism Testable?

  • Predictive Equivalence

  • Prediction versus Accommodation

  • Does Evolutionary Theory Make Novel Predictions?

  • Concluding Remarks

Creationism

  • Present-day advocates of the design argument include scientific creationists and intelligent design theorists.

  • There is a division among creationists regarding the age of the Earth:

    • Some assert a young Earth (around 10,000 years old).

    • Others accept an ancient Earth (approximately 4.5 billion years old).

  • Disagreement also exists about whether every species was created separately or if all species trace back to a common ancestor.

Clarification of Creationism's Assertions

  • Three possible relationships concerning God (G), evolutionary processes (E), and adaptations (O):

    • Theistic Evolutionism: G E O

    • God initiates evolution, which then explains complex adaptations.

    • Atheistic Evolutionism: E O

    • Accepts evolution (without a God).

    • Creationism: G > E O

    • Asserts that God's intervention is necessary for complex adaptations, rejecting solely natural explanations of evolution.

Differences Between Evolutionary Theory and Creationism

  • Neutrality of Evolutionary Theory:

    • Evolution does not deny the existence of God or support atheism and accommodates agnosticism.

    • Creationism explicitly denies that evolution can account for complex adaptations.

Some Creationist Arguments

  • Common creationist claims against evolutionary theory often rely on misconceptions:

    • Evolution cannot achieve absolute certainty about the past (true, but all science operates on probabilistic evidence).

    • The Second Law of Thermodynamics is frequently misinterpreted to assert that order cannot arise from disorder:

    • The law applies to closed systems, whereas Earth is not a closed system due to energy influx from the sun.

    • The emergence of order from natural processes is therefore feasible if the system is open.

  • Evaluation of claims made by creationists reveals a lack of robust alternative explanations.

    • Young Earth creationism contradicts established geological and physical evidence.

Darwin's Two-Part Theory

  • Darwin’s theory, primarily articulated in The Origin of Species, includes two main elements:

    • Common Descent:

    • All living organisms are genealogically related and evolved from common ancestors via descent with modification.

    • Distinct species were not independently created.

    • Natural Selection:

    • Explains how new characteristics develop and affect the evolution of species.

    • Important to keep distinct from common descent as the former is often debated more than the latter.

Natural Selection

  • Example of natural selection using zebras:

    • In a population where all zebras run at 38 mph, a mutation occurs creating a faster zebra (42 mph).

    • Faster zebras have increased survival likelihood, leading to greater reproduction and an eventual population shift toward the new trait.

    • Two stages of natural selection:

    • Mutation introduces variation.

    • Frequency of traits changes based on fitness.

  • Requirements for natural selection to occur:

    • Inherited variation among organisms.

    • Variations must affect fitness (survival and reproduction).

    • The frequency of characteristics in the population will evolve if these conditions are met.

Clarification of Mutations and Traits

  • Mutations are random and do not occur for the purpose of enhancing the organism; they form the basis for natural selection.

  • Creationist analogies (e.g., tornado in a junkyard) misconstrue the process by overlooking the non-random nature of selection.

  • Darwin's analogy of a builder with uncut stones illustrates the relationship between random mutations created by natural laws and purposeful construction through natural selection.

Speciation

  • Speciation explains how small changes can accumulate in populations leading to the emergence of distinct species.

  • Scenario of zebras separated by geographical barriers illustrates divergence due to environmental adaptations leading to reproductive isolation.

  • Resistance to Darwin's thesis about the link between small changes and the emergence of new species was prevalent, although mainstream evolutionary theory now accepts this concept.

Remaining Questions

  • Biologists still explore unanswered questions in evolutionary biology, such as the evolution of sexual reproduction.

The Tree of Life

  • Biologists draw conclusions about the common ancestry of life from compelling argumentative lines based on two types of evidence:

Argument from Similarity

  • Similarities in living organisms are expected if they share a common ancestor.

    • Example: If two identical essays are submitted, the simpler explanation of a common source is more likely than independent coincidence.

Principle of the Common Cause

  • Originating from Hans Reichenbach, this principle holds that observed correlations are often attributed to a common cause rather than coincidence.

Arbitrary Similarities among Organisms

  • Shared genetic codes across various species indicate common ancestry; this is crucial for understanding biological relationships.

Useful Similarities among Organisms

  • Not all similarities indicate common ancestry; functional adaptations can independently arise. Example: Streamlined shapes of sharks and dolphins, which do not necessarily suggest a common ancestor.

Shared but Non-Functional Features

  • Features like human tailbones or gill slits in fetuses represent non-functional remnants pointing to evolutionary past.

    • These serve as evidence of common ancestry through the Surprise Principle and the Principle of the Common Cause.

Irreducible Complexity

  • Definition by Michael Behe:

    • An irreducibly complex system is one wherein the system's function relies on all its parts; removal of one part nullifies function.

Challenge to Evolution

  • Creationists argue that certain biological structures, like the vertebrate eye, cannot logically evolve through gradual selection because they require all parts to function adequately.

Humans from Nonhumans, Life from Nonlife

  • Evidence for common ancestry with nonhuman ancestors is rooted in striking similarities; evolutionary details are still under study.

  • The idea that life evolved from nonlife is supported by laboratory experiments.

    • Early conditions can form organic molecules through natural processes, establishing a basis for biological evolution.

Is Creationism Testable?

  • Creationist theories vary significantly, some asserting perfect design while others accommodate flaws.

    • Example of Hypotheses:

    • H₁: A superintelligent designer created perfect adaptations (disconfirmed by evidence of imperfections).

    • H₃: If God created species with specific characteristics to resemble those resulting from evolution, this predicts no distinguishable outcomes from evolutionary theory.

Predictive Equivalence

  • When two theories (i.e., evolution and creationism) arrive at the same predictions, it becomes challenging to differentiate between the two based on observational evidence alone.

Prediction versus Accommodation

  • Creationism can often accommodate observations without providing novel predictions—this serves as a limitation.

  • Evolutionary theory is seen as requiring predictions that extend beyond observational accommodation.

Does Evolutionary Theory Make Novel Predictions?

  • Evolution outlines clear predictions about common ancestry reflected in the fossil record.

    • Fossils serving as intermediates between species reinforce the theory of evolution.

    • The theory facilitates predictions regarding traits favorited by natural selection across various contexts.

Concluding Remarks

  • Creationism exists in various forms, with many lacking testable predictions or making predictions inconsistent with observed evidence.

  • Evolutionary theory continues to offer robust and predictive explanations for the diversity of life as observed in current scientific understanding.

Review Questions

  1. What are the two main elements of Darwin's theory?

  2. Describe what the Principle of the Common Cause says. How is this principle related to the Surprise Principle? How is it used by biologists to decide whether different species have a common ancestor?

  3. Explain François Jacob's metaphor about natural selection and its implications.

  4. What does it mean to say that two theories are predictively equivalent? Can the design hypothesis be formulated to accommodate evidence of imperfect adaptations?

Problems for Further Thought

  1. Discuss whether Pasteur's discoveries about spontaneous generation impact the idea that life evolved from nonliving materials.

  2. Given a hypothetical encounter with intelligent life, which observations would be relevant to determine contact with Earth?

  3. Compare the arguments of Paley and Behe regarding intelligent design and irreducible complexity.