Evidence of Evolution – AP Biology College Board Revision

Understanding Evidence of Evolution

Evolution is a gradual change in organisms over time, moving from simple life forms to the diverse species we see today.
This concept can be difficult to grasp because the alterations are often slow and occur over hundreds or thousands of generations.
However, a substantial amount of evidence exists that clearly reveals the process of evolution.

Fossils provide one of the primary forms of evidence supporting the theory of evolution.
Fossils present in rock layers provide a historical record of past life forms. The deeper the layer, the older the fossil.
By comparing fossilised remains across different strata (layers), scientists can trace changes in different species over time.
A series of fossils documenting gradually changing features in a species is known as a transitional series.
Examples of transitional series include the evolution of the horse, the whale, and human beings.

DNA is the building block of life, and similarities in the DNA code between different species suggest a common ancestor.
Comparative genomics, the study of similarities and differences in the DNA of different species, has provided strong support for evolutionary theory.
For instance, humans share around 98% of their DNA with chimpazees, our closest non-human relatives.
The more closely related species are on the evolutionary tree, the more alike their DNA sequences will be.

Anatomical evidence includes structures in different species known as homologous structures, which originate from a common ancestor but may serve different functions in modern species.
A classic example of this is the similarity in the bone structures in the limbs of humans, cats, whales, and bats, suggesting they all evolved from a common ancestor.
Structures which no longer serve a specific function but persist because they were part of an ancestor’s anatomy are called vestigial structures. A human example is the appendix.

The geographic distribution of species, known as biogeography, also provides evidence for evolution.
The specific mix of wildlife on each continent signifies that life has evolved separately under different conditions and timings.
Charles Darwin famously argued for his theory of evolution based on his observations of species variation across geographical locations during his voyage on the HMS Beagle.
For instance, the finches on the Galapagos Islands showed small differences in beak structure in accordance with specific diets, signifying adaptive evolution.

Evolution has been directly observed in certain species that reproduce quickly. This has been documented in laboratory settings and in the natural environment.
Antibiotic resistance in bacteria is a current and significant demonstration of observable evolution in action.
In the face of antibiotic use, bacteria populations evolve resistance to treatments, resulting in the need for different and stronger antibiotics.
This phenomenon, also known as microevolution, validates the overall concept of evolution.