Unit B

Module 4 ~ Lesson 3

 Evidence for Evolution


A variety of evidence for evolution exists. This includes the following:

  1. the fossil record
  2. transitional fossils
  3. biogeography
  4. anatomy
  5. embryology
  6. molecular biology and genetics
Trilobite fossils can be found in Alberta and all over the world. Trilobites became extinct about 245 million years ago, but at one time, there were more than 17,000 different species of them. The closest living relative to trilobites is likely the horseshoe crab. 



Image by Pexels from Pixabay

The Fossil Record


Fossils provide a record of species that were alive in the past, from early micro-organisms to species of animals that are alive today. The fossil record provides evidence about the relative age of fossilized species.

Fossils appear in chronological order in the rock layers, or strata, with fossils in the youngest layers appearing most closely related to modern species. Strata layers are generally not visible since the older layers are covered by newer layers. However, in some locations,  for example, the Grand Staircase in Utah, geological events have left these layers exposed. Another location where these layered are exposed and easily studied is right here in Alberta's Badlands .  



U.S. Federal Government. [Public Domain]. via Wikimedia Commons,

Studying the order of the fossils can help determine their age since the strata are found in chronological order. The order of the fossils can also help scientists organize evolutionary family trees. Not all fossils appear in the record at the same time, which can help scientists figure out the evolutionary lines between ancestors and living species. 


By Ghedoghedo [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)], from Wikimedia Commons

Transitional Fossils

Transitional fossils are fossils of organisms that show links between groups of organisms and represent an organism at the point where individual lineages diverge.

Fossil evidence suggests that whales evolved from a terrestrial ancestor such as Ambulocetus natans (left, bottom). The fossil of Ambulocetus natans suggests that it walked on land and swam in the water. The transitional fossil, Dorudon (left, top), is an ancient whale with remnants of tiny hind legs.

Patterns of Distribution

Biogeography  is the study of the past and present geographical distribution of organisms. Species distribution, both current and from the fossil record, supports the theory of evolution by natural selection based on a variety of examples.

  • Geographically close environments are more likely to have related organisms than environments that are separated but similar. 
  • Island species tend to resemble mainland organisms from the closest continent.
  • Fossils of the same species have been found on coastlines of neighbouring continents.
At one time, all of the continents were linked together and referred to as Pangaea. The movement of the continental plates helps to predict when and where animals evolved.

Courtesy of the U.S. Geological Society

 Read

Read "Further Evidence of Evolution" on pages 126 to 133 of your textbook.

 Self-Check

Archaeopteryx has characteristics of both reptiles (dinosaurs) and birds. It had feathers, but it also had teeth, claws, and a bony tail.
They broke apart from 110 to 120 million years ago.
India became part of Asia from 23 to 30 million years ago.
Africa and South America were once joined in one "supercontinent."
Antarctica and the North Pole were not connected when penguins and polar bears evolved.

Biology 20 © 2008