Transcript Document

Changes Over Time Evolution by Natural Selection

Charles Darwin

Burning Questions… If there are millions of organisms on earth in every shape, size, color…

How did they arise?? ?

How are they related?

Darwin’s Theory of Evolution 


, or change over time, is the process by which modern organisms have descended from ancient organisms.  A scientific


is a well-supported testable explanation of phenomena that have occurred in the natural world.

How do you think Darwin came up with his theory?

Voyage of the Beagle

Voyage of The Beagle 


February 12th, 1831 


: H.M.S. Beagle 


Voyage around the world.


evidence to propose a revolutionary hypothesis about how life changes over time.  Science would never be the same again!

Patterns of Diversity  Darwin visited similary ecosystems and biomes around the world and noticed that there sometimes there were very different animals living there  Neither Argentina nor Australia was home to the sorts of animals that lived in European grasslands.

 Why aren’t there kangaroos in England?

Living Organisms and Fossils  Darwin collected the preserved remains of ancient organisms, called


.  Some of those fossils resembled organisms that were still alive today.

Living Organisms and Fossils  Others looked completely unlike any creature he had ever seen.  As Darwin studied fossils, new questions arose.  Why had so many of these species disappeared?  How were they related to living species?


The Galapagos Islands  The smallest, lowest islands were hot, dry, and nearly barren  -Hood Island-sparse vegetation  The higher islands had greater rainfall and a different assortment of plants and animals  Isabela- Island had rich vegetation.

The Galapagos Island  Darwin was fascinated in particular by the land tortoises and marine iguanas in the Galápagos.  Giant tortoises varied in predictable ways from one island to another.

 The shape of a tortoise's shell could be used to identify which island a particular tortoise inhabited.

Animals found in the Galapagos  Land Tortoises  Darwin Finches  Blue-Footed Booby  Marine Iguanas


Soooo… Darwin began to hypothesize… 


Separate species may have arisen from an original ancestor  But over time, those species separated because of characteristics that developed over time based on the environment where the species lived.

Evolution by Natural Selection 

The Struggle for Existence

-members of each species have to compete for food, shelter, other life necessities 

Survival of the Fittest

-Some individuals better suited for the environment

Natural Selection 


-differences among individuals of a species (Color, size, etc.) Caused by mutations or are shaped by conditions in the environment

Struggle For Existence & Survival of The Fittest Sometimes variations Give certain animals or plants an “edge” over others.  Nature “selects” certain animals to survive and pass along their characteristics to the next They can get stronger, live longer and reproduce generation. And pass along their good genes to their offspring.

Natural Selection  Over time, natural selection results in changes in inherited characteristics of a population.  These changes increase a species’ “fitness” for its environment


An inherited trait that increases an organism’s chance of surviving, reproducing in its environment. Three types: Behavioral Structural Functional

*(Check out the other ppt on my website!)

Adaptations help organisms survive: Camouflage Allows organism to blend in with their environment Mimicry Resemblance of one species to another species

Evidence for Evolution 

Vestigial organs

-organs that no longer serve a useful function in an organism  i.e.) appendix, wisdom teeth, 5 th claw on dog or cat

Homologous Structures 

Body parts of organisms that are similar in structure and position but different in function

Analogous Structures

 Body parts that perform a similar function but differ in structure

Similarities in Early Development Pharyngeal Pouches