Is the contemporary theory of evolution an example of good science? The answer to this question completely depends on how you define “science,” and what you think makes science “good.”
Good science has an addiction to theories,1 and for science to be good science, it must deal with good scientific theories. What constitutes a good scientific theory? That is a very involved question, but a user’s view of good scientific theories looks something like this:
- A scientific theory is not a guess or suspicion. For example, “I have a theory about who shot President Kennedy,” reflects the colloquial meaning of the word “theory,” and not the meaning conveyed by scientists when they use the word “theory.”
- Scientific theories are convincing explanatory frameworks that efficiently integrate a large body of evidence about the world. Good scientific theories have the capacity to make sense of a wide range of data that made less sense before the introduction of the theory.
- In order to be called a scientific theory, it must have been successfully tested and re-tested many times.2
- A scientific theory must be falsifiable in order to be truly scientific. The theory has to live constantly at risk from new data.3
- A theory must have predictive power.4 Good theories allow scientists to make predictions based on the theory that, when tested, turn out to be at least roughly correct.
These are not the only characteristics of a scientific theory, but they probably represent the most important features for practitioners of science.
If we hold contemporary evolutionary theory to these standards, how well does it do? Since the inception of evolutionary theory by Charles Darwin in 1859 with the publication of On the Origin of Species, there are four characteristics of evolutionary theory that have endured 150 years of further research:
- Living species are descendants of other species that lived in the past.
- These past species lived in populations that underwent gradual transformation so that the individuals in these populations changed their appearance, behaviors, metabolisms, and life histories over long spans of time.5
- New forms of life arose by means of a process called speciation in which one lineage splits into two distinct lineages. This continual splitting of organismal lineages leads to a nested genealogy of species. This nested genealogy forms a veritable tree of life, whose root represents the first species to arise and whose twigs represent the millions of species living today. If you trace back any pair of twigs from the modern species you will find that their histories merge at some node on the tree where the two species share a common ancestor.6
- This process of biological change that takes place throughout the advance of geologic time, or evolution, occurs by means of variation in organisms (which we know today is due to genetic mutations) that is acted on by either random genetic drift or natural selection. Those individuals with variations better suited to the current environment leave more offspring, thus changing the average appearance of the population over time and making it a better fit to the environment. This improving fit between organisms and their environment gives the appearance of organisms having been well designed for their milieu.7
What is the evidence for these aspects of evolutionary theory? The evidence is actually immense, but I will restrict this discussion to just a few items.
First there is the fossil record. If life results from a natural process such as biological evolution, then we should observe a progression of fossil organisms that proceed from relatively simple, single-celled organisms in the oldest rocks to more complex, multicellular organisms in younger rocks. When paleontologists examine the geologic column, they perceive that some of the oldest and deepest layers of the geologic column contain fossils of microorganisms, and then marine invertebrates in younger layers above those,8 and then much later and higher up in the geologic column fish appear, followed later and higher still by amphibians, and then by reptiles, mammals, and birds.9 Thus, the general presentation of the fossil record in the rock record comports exactly with what the theory of evolution predicts.
However, the fossil story gets even better, because scientists can trace evolutionary trends throughout the fossil record. For example, horses get bigger, fuse their leg bones and toes into a single bone with a thick hoof and grow the thickness of their tooth enamel;10 Cenozoic brachiopod shells get narrower, decrease their rib numbers and beak angle;11 diatoms get bigger;12 and primate fossils reduce the size of their teeth and expand the size of their brains.13
Additionally, Darwin predicted that there should be organisms preserved in the fossil record that possess features found in two different types of creatures. Such organisms are “transitional forms” that bridge the gap between different types of organisms.14 However, the fossil record of Darwin’s time provided little evidence of such transitional forms.15 Therefore, Darwin gambled that future paleontological research would provide sufficient evidence to corroborate his theory. How did this gamble turn out? Since Darwin’s time, paleontologists have discovered transitional fossils that are part fish and tetrapod,16 part amphibian and part reptile,17 part dinosaur and part bird,18 and part reptile and part mammal.19 Once again, we would predict such paleontological trends and the existence of such transitional fossils if life came about through a process of organic evolution. Clearly paleontological research since Darwin’s time has powerfully vindicated his theory.
Please join us for part two of this post tomorrow, where we will discuss how signs of evolution can be detected in organisms living today, and how evidence from multifarious scientific fields—not just biology and paleontology—have bolstered the theory of evolution and added to our understanding of how natural selection works.
1. Ratzsch, Del. The Battle of Beginnings: Why Neither Side Is Winning the Creation-Evolution Debate. Downer’s Grove, WI: Intervarsity Press, 1996. pp. 104–119.
2. Kitcher, Philip. Abusing Science: The Case Against Creationism. Cambridge, MA: MIT Press, 1983. pp. 45–54.
3. Ibid, 42–48. .
4. Ratzsch, Del. Science and Its Limits: The Natural Sciences in Christian Perspective. Downer’s Grove, WI: Intervarsity Press, 2000. pp. 21–24.
5. Hall, Brian K., and Benedikt Hallgrimsson. Strickberger’s Evolution. 5th ed. Burlington, MA: Jones and Bartlett, 2013. pp. 19–68.
6. Kitcher, Philip. Living With Darwin: Evolution, Design, and the Future of Faith. New York: Oxford University Press, 2009. pp. 43–71.
7. Futuyma, Douglas J. Evolution. 3rd ed. Sundbury, MA: Sinauer Associates, 2013. pp. 281–343.
8. Valentine, James W. On the Origin of Phyla. Chicago: University of Chicago Press, 2006. pp. 429–464.
9. Carroll, Robert L. Vertebrate Paleontology and Evolution. New York: W. H. Freeman and Company, 1990.
10. MacFadden, “Horses, the Fossil Record, and Evolution,” 131–158; McFadden, Bruce J. “Fossil Horses from “Eohippus” (Hyracotherium) to Equus: Scaling, Cope’s Law, and the Evolution of Body Size.” Paleobiology 12, no. 4 (1986): 355–69.; Prothero, Donald R., and R.M. Schoch, eds. The Evolution of Perissodactyls. New York: Clarendon Press, 1989. ; McFadden, Bruce J. Fossil Horses. Systematics, Paleobiology, and Evolution of the Family Equidae. Cambridge, Cambridge University Press, 1993.
11. McNamara, Kenneth J. “Evolutionary Trends.” In Encyclopedia of Life Sciences (New York: Macmillan Publishers Ltd, 2001), pp. 1–7.
12. Litchman, E., C. A. Klausmeier, and K. Yoshiyama. “Contrasting Size Evolution in Marine and Freshwater Diatoms.” Proceedings of the National Academy of Sciences USA 106, no. 8 (2009): 2665–2670.
13. Tattersall, Ian. The Fossil Trail: How We Know What We Think We Know About Human Evolution. New York: Oxford University Press, 2008. pp. 89–198.
14. Darwin, Charles. On the Origin of Species by Means of Natural Selection or the Preservation of Favoured Races in the Struggle for Life. London: Penguin Books, 1985. p. 292.
15. Hunt, Gene. “Evolution in Fossil Lineages: Paleontology and The Origin of Species.” Supplement American Naturalist 176 (2010): S61–S76.
16. Clack, Jennifer A. Gaining Ground: The Origin and Evolution of Tetrapods. Bloomington, IN: Indiana University Press, 2002; Daeschler, Edward B., Neil H. Shubin, and Farish A. Jenkins, Jr. “A Devonian Tetrapod-Like Fish and the Evolution of the Tetrapod Body Plan,” Nature 440, no. 7085 (2006): 757–63; Shubin, Neil H., Edward B. Daeschler, and Farish A. Jenkins, Jr. “The Pectoral Fin of Tiktaalik roasae and the Origin of the Tetrapod Limb.” Nature 440, no. 7085 (2006).): 764–71; Downs, Jason P., Edward B. Daeschler, Farish A. Jenkins, and Neil H. Shubin. “The Cranial Endoskeleton of Tiktaalik roseae.” Nature 455, no. 7215 (2008): 925–9.
17. Carroll, Robert L. Vertebrate Paleontology and Evolution. New York: W. H. Freeman and Company, 1990. pp. 156–216.
18. Shipman, Pat. Taking Wing: Archaeopteryx and the Evolution of Bird Flight. New York: Touchstone, 1998. pp. 169–244.
19. Prothero, Donald R. Evolution: What the Fossils Say and Why It Matters. New York: Columbia University Press, 2007. pp. 271–297.