In this last unit of the trimester we will learn about how organisms have changed over time based on the adaptations that have enabled them to survive. These adaptations are the accumulation of genetic mutations that have occurred in the DNA over many, many years, changing the organism so much from its original state that new species have arisen.

We begin by studying Charles Darwin and his theory of Natural Selection. He states:

  • Species (populations of interbreeding organisms) change over time and space. The representatives of species living today differ from those that lived in the recent past, and populations in different geographic regions today differ slightly in form or behavior. These differences extend into the fossil record, which provides ample support for this claim.

  • All organisms share common ancestors with other organisms. Over time, populations may divide into different species, which share a common ancestral population. Far enough back in time, any pair of organisms shares a common ancestor. For example, humans shared a common ancestor with chimpanzees about eight million years ago, with whales about 60 million years ago, and with kangaroos over 100 million years ago. Shared ancestry explains the similarities of organisms that are classified together: their similarities reflect the inheritance of traits from a common ancestor.

  • Evolutionary change is gradual and slow in Darwin’s view. This claim was supported by the long episodes of gradual change in organisms in the fossil record and the fact that no naturalist had observed the sudden appearance of a new species in Darwin’s time. Since then, biologists and paleontologists have documented a broad spectrum of slow to rapid rates of evolutionary change within lineages.

We will then study the various pieces of evidence that support evolution, including fossils, homologous structures, DNA/amino acid sequencing, and adaptations. We will simply be touching on each one of these so that you have a working understanding of how they support evolution.



The above picture shows the variety in finches that Darwin found on the Galapagos Islands.


The above picture shows you examples of some homologous structures among different organisms.


***handout from class

Summary Videos: