Empirical Evidence For Evolution In The Fossil Record
In his groundbreaking publication On The Origin Of Species in 1859, Charles Darwin recognized the lack of transitional species in the fossil record to support his theory at that time. He argued that the fossil record would likely give us a poor sampling due to large gaps and he blamed the imperfection of the geological record. While traveling around the world as a Naturalist aboard The Beagle, Darwin collected fossils whenever he could. He noticed that extinct species often were similar to modern species in the area they were collected, but yet they also were distinct. Darwin speculated not only about the reason so many animals went extinct, but also about why they showed variation in size or minor details from extant species. South American sloths, armadillos, and the common Rhea are good examples (1). From this observable, empirical evidence gathered by studying endemic species he hypothesized that the animals must have changed slowly over time. Little did Darwin know that the fossil record would become one of the main sources of evidence for evolution by natural selection.
Every scientific theory must be testable and make falsifiable predictions and the predictive power of Darwin’s Theory of Evolution based on empirical evidence in the fossil record is now well established. In his book Your Inner Fish, Neil Shubin describes how he predicted we would find a transitional species in between known extinct fish and reptiles. He was looking for a fish to amphibian transition and based on previous discoveries his team calculated the missing transition should be found in strata 375 million years old. They located a likely exposed layer of that age on Ellesmere Island in northern Canada, and after two seasons of searching, his team found the transitional fossil now nicknamed Tiktaalik which showed characteristics of fish, amphibians, and reptiles (2). While Tiktaalik and its species may not be our direct ancestor, it shows the emergence of key features that continue on in the fossil record such as a neck that can bend independently of the body, and fin bones that are homologous to reptile and mammal arms and hands. Both of these features continued on in reptiles and mammals that evolved much later and still exist today. This also gives support to the idea of descent with modification from a common ancestor, another key feature of Darwin’s Theory of Evolution.
Empirical evidence is data or information gained by direct observation or by means of the senses (3). Does the fossil record qualify as empirical evidence? Some would argue if we were not there to see the animal alive we cannot know for sure what it looked like or how it is different from the later species into which it evolved. I would argue that not only are individual fossils empirical evidence, but the entirety of the fossil record also stands as empirical evidence for Darwin’s Theory of Evolution by showing evolution over time. Modern paleontologists compare minute changes from species to species as they are seen in successive geological strata and it shows a chronology of change from one type of animal to another. Fish to amphibian, amphibian to reptile, and reptile to mammal evolution are all good examples of this based on empirical evidence. In addition to learning about animal life in the fossil record, we also have evidence for what the environments looked like and how they changed over time by studying the plant life throughout the geologic column. Since environmental pressures drive natural selection this data is also very important. The entirety of the fossil record, including plants and animals, is truly empirical evidence for the Theory of Evolution.
1. Charles Darwin’s Evidence for Evolution by Dr. Niles Eldredge
2. Your Inner Fish by Neil Shubin, Vintage Books, 2008
3. Empirical Evidence: A Definition, Live Science Magazine, March 2015