12 Chapter 12: Evolution
Chapter Outline
12.1 Evidence for Evolution
- Fossil Record
- Homology
- Biogeography
12.2 Mechanism of Evolution: Natural Selection
- Principles of Natural Selection
- Demonstrations of Natural Selection
12.3 Other Mechanisms of Evolution
All species of living organisms—from the bacteria on our skin, to the trees in our yards, to the birds outside—evolved at some point from a different species. Although it may seem that living things today stay much the same from generation to generation, that is not the case: evolution is ongoing. Evolution is change over time—it is the process through which the characteristics of species change and through which new species arise.
The theory of evolution is the unifying theory of biology, meaning it is the framework within which biologists ask questions about the living world. Its power is that it provides direction for predictions about living things that are borne out in experiment after experiment. The Ukrainian-born American geneticist Theodosius Dobzhansky famously wrote that “nothing makes sense in biology except in the light of evolution”[1] He meant that the principle that all life has evolved and diversified from a common ancestor is the foundation from which we understand all other questions in biology. This chapter will explain some of the mechanisms for evolutionary change and the kinds of questions that biologists can and have answered using evolutionary theory.
Learning Objectives
- You will be able to describe the various lines of evidence for the evolution of life, including the fossil record, biogeography, vestigial traits, and various types of homologies.
- You will demonstrate the process of evolution, which results in increasing the diversity and complexity of life. Specifically, you will understand and provide examples of adaptation through natural selection, which requires the following factors:
- operates on populations in specific environmental contexts
- necessary because of the competition for limited resources
- relies on biological processes that produce of new variation
- transfers new variation through the mechanisms of inheritance
- results in differential fitness (differences in survival and reproduction)
12.1 Evidence for Evolution
The evidence for evolution is compelling and extensive. Looking at every level of organization in living systems, biologists see the signature of past and present evolution. Darwin dedicated a large portion of his book, On the Origin of Species, identifying patterns in nature that were consistent with evolution and since Darwin our understanding has become clearer and broader.
12.1.1 Fossil Record
Fossils are the preserved partial remains (usually only hard bony tissue or shells survive but occasionally soft tissue remains are also preserved) of living organisms that have been buried and protected from the elements that cause decomposition and degradation. The remains are slowly transformed as minerals from the surrounding se