Aim: What is Darwin’s Theory of Natural Selection ? Do the activity with your group. Look at the picture, discuss and answer the questions. How did this organism change over time? List the changes in structure that you notice in each picture What may have caused these changes?

Land Water

Water carries small rock particles to lakes and seas. Dead organisms are buried by layers of sediment, which forms new rock. The preserved remains may later be discovered and studied. Section 17-1 Figure 17-2 Formation of a Fossil Go to Section: The fossil record provides evidence about the history of life on Earth Evolution: Library: Permian-Triassic Extinction

Darwin’s Dilemma was…

Among the birds that ended up in arid environments, the ones with beaks better suited for eating cactus got more food. As a result, they were in better condition to mate. Similarly, those with beak shapes that were better suited to getting nectar from flowers or eating hard seeds in other environments were at an advantage there. In a very real sense, nature selected the best adapted varieties to survive and to reproduce. This process has come to be known as natural selection Finches from the Galapagos Islands

Aim: What does the Origin of Species tell us? Jigsaw the reading and answer content questions on page 64 one person reads Struggle for Existence and answers q. 1-3 on page 67 Share the answers with your group

Summary of Darwin's Theory of Evolution A species is a population of organisms that interbreeds and has fertile offspring. Living organisms have descended with modifications from species that lived before them. Natural selection explains how this evolution has happened: More organisms are produced than can survive because of limited resources. Organisms struggle for the necessities of life; there is competition for resources. Individuals within a population vary in their traits; some of these traits are heritable -- passed on to offspring. Some variants are better adapted to survive and reproduce under local conditions than others. Better-adapted individuals (the "fit enough") are more likely to survive and reproduce, thereby passing on copies of their genes to the next generation. Species whose individuals are best adapted survive; others become extinct.

Natural Selection of the Peppered Moth The 'textbook story' of England's famous peppered moths (Biston betularia) goes like this. The moth comes in light and dark (melanin) forms. Pollution from the Industrial Revolution darkened the tree trunks, mostly by killing the light-colored covering lichen (plus soot). The lighter forms, which had been well camouflaged against the light background, now 'stood out', and so birds more readily ate them. Therefore, the proportion of dark moths increased dramatically. Later, as pollution was cleaned up, the light moth became predominant again.

Adaptations and Survival How does camouflage help organisms survive?