1. Unit 6: Evolution The process of change over time Charles Darwin developed the theory of how living things evolve

2. Darwin's Theory of Evolution Based on his findings on the Galapagos Islands and elsewhere, Darwin said that all living things are descended (with modifications) from a common ancestor. “Descent With Modification”

3. Descent with Modification The Earth is about 4.5 billion years old The first living cells (similar to bacteria) are believed to have appeared on Earth about 3.5 billion years ago Darwin theorized that all living things on Earth are descendants of an ancient organism from the past. This ancient organism is the “common ancestor” for all living things on Earth.

4. Descent with Modification (cont.) Small changes every generation for billions of years have led to different organisms branching off into new species, and forming the “Tree of Life”. We now know that these small changes occur in the DNA as mutations.

5. How does Decent with Modification occur? Darwin proposed that evolution occurs by Natural Selection Natural Selection- the process by which organisms with variations most suited to their environment survive and leave more offspring.

6. How Natural Selection Works A. “The Struggle For Existence” - If more individuals are born than can survive, there must be competition for food, living space, etc. - Darwin wanted to know which individuals would come out on top

7. How Natural Selection Works B. “Variation and Adaptation” - Some variations in individuals are better suited for a certain environment - Adaptation- any heritable characteristic that increases an organism’s ability to survive in a certain environment - Well adapted individuals survive and reproduce Yeti Crab

8. How Natural Selection Works C. “Survival of the Fittest” - Fitness- how well an organism can survive and reproduce in its environment - If an organism is well adapted to its environment and successfully reproduces it has “high fitness” - Over time, the traits of the well adapted individuals become the more common traits of the population Snowy egret nest

9. Example of Natural Selection 1. Grasshopper lays eggs 2. Yellow and green grasshoppers hatch 3.Predator eats the grasshoppers that are easy to see 4.Green grasshoppers are left to reproduce After many generations, almost all grasshoppers will be __________. green Thus, nature has “selected for” green grasshoppers!

10. Patterns of Evolution

11. 1. Divergent Evolution- the accumulation of differences between organisms of a species which can lead to the formation of new species Involves speciation through adaptive radiation

12. Speciation is how divergent evolution occurs - A species is a population or group of populations whose members can interbreed to produce fertile offspring - Speciation- the formation of a new species The Galapagos finches underwent speciation

13. How does Speciation Occur? When two populations can no longer interbreed, the gene pool will split This is called reproductive isolation Reproductive isolation can lead to the formation of two separate species or divergent evolution

14. The process by which a single species or small group of species evolve over a relatively short period of time into several different forms that live in different ways Adaptive Radiation leads to speciation

15. Reasons why Adaptive Radiation Occurs A. Species migrate to a new environment B. Extinction clears an environment of many inhabitants - Example: after the dinosaurs became extinct, mammals were able to reproduce and survive more, spread out, and diversify. C. A species evolves a new feature that allows it to live in a new environment - Example: Galapagos finches developed different beaks to allow them to eat different types of food on the different islands.

17. 2. Convergent Evolution When organisms in different locations, but similar environments evolve in a similar way. Natural selection may cause different body structures to have similar functions. Example: rheas (South America) and ostriches (Africa) are both birds that lost their ability to fly Rhea- South America Ostrich- Africa

18. 3. Coevolution The process by which two species evolve over time in response to changes in each other. Often species that coevolve can not survive without each other. Example: flowers and pollinators (organisms that cause the pollen (sperm) to reach the egg of a flower)

19. Example of Coevolution The Madagascar Star Orchid and HawkmothMadagascar Star Orchid and Hawkmoth – The orchid has a long tube with nectar (food) at the bottom – The moth has a long tongue to reach the nectar – When the moth eats, it rubs against the pollen of the flower, and brings it to other flowers – Over generations, as the moth’s tongues get longer, the orchid’s tube gets longer so that the moth will always rub against the pollen.

20. Flowers and Pollinators Pollination Beauty of Pollination