Contrary to popular belief science is more than controlled experiments that are conducted in laboratories. Much of science is accomplished by gathering evidence from the real world and inferring how things work.
Physicists cannot zoom in on atoms, not even with a microscope. Astronomers cannot reach the stars. Geologists cannot go back in time. However, scientists can learn a great deal, by using multiple lines of evidence to make valid and useful inferences about their objects of study. The study of evolutionary biology does not have to rely on observable evolution.
That evolution is not observable is quite often given as a reason why we can not be sure of the truthfulness of evolutionary theory. Fortunately, there are certain cases for observable evolution.
In 1971, an evolutionary experiment was conducted on five male and five female Italian wall lizards. As part of this experiment, scientists relocated the lizards from their original island home in Pod Kopiste to the tiny neighboring island of Pod Mrcaru. Scientists specifically chose Italian wall lizards for their comparatively short generation time. The Italian wall lizards reach maturity when they reach about 2 inches, which takes one year for males, and between one and two years for females.
The test plan of the experiment took an unexpected turn when the Croatia War of Independence broke out in 1991, which caused scientists to lose access to Croatia. It was not before 2004 when scientists were able to go and check the course of their experiment.
The new habitat of the lizards had an abundance of plants that the test subjects were not built to digest. When the scientists returned to Pod Mrcaru the scientists discovered that there were important changes with the digestion system of test subjects’ descendants.
- Lizards developed new muscles between their large and small intestines to slow down their food digestion.
- Their guts expanded to processes their new diet.
- Lizards now had a longer and wider head to bite their food harder.
Based on the complexity of the species, and the length of their generation time the evolution of a species may be observable or non-observable for humans. For example, Italian Wall lizards are relatively less complex animals and their generation time is less than two years. Hence, we can observe the evolution of lizard’s inheritable traits in our lifetime. When it comes to evolution, however, we must rely on evidence.
It is estimated that on earth,
- life 3700 million years ago
- multicellular organisms 600 years million years ago
- amphibians 370 million years ago
- mammals 210 million years ago
- apes 50 million years ago
- humans 2 million years ago,
- modern humans 0.2-0.3 million years ago
Clearly no one was around to observe our evolutionary chain, from unicellular organism to homo sapience. Yet, we still know a quite deal about our ancestors.
Evolutionary biologists are not any different than the defectives who come at the scene of a murder that was committed with no eye-witnesses. In order to solve such crimes, the detectives often rely on scientific records of past behavior such as matching fingerprints or DNA, analyzing bloodstain patterns. Similarly in order to understand the diversity of species on Earth evolutionary biologists use, among others, anatomy, DNA, and shared genetic code with ancestry, fossils, direct observations of other species’ evolution.
Although we cannot run an experiment that will tell us how the dinosaur lineage radiated, we can study many aspects of evolution with observations in a laboratory setting, or in the case of Italian wall lizards in the wild. Since it would be counterproductive to wait 40 years to assess our experiments, instead we use bacteria whose generation time can be as short as 12 minutes.
If we place such a one-celled organism under a microscope, we can observe how that cell multiplies keeping its original DNA intact. However, given enough time, before our eyes under a microscope new organisms would emerge that have minor differences in their DNA. In time these differences would accumulate and we would get groups of organisms that have remarkable differences in DNA compared to each other.