Natural Selection

Who came up with this theory of evolution? Charles Darwin

Who was Charles Darwin? He Came up with the mechanism for evolution He was from England Attended medical school at 16 and dropped out Attended theology school and dropped out Became interested in biology Joined a voyage on the HMS Beagle at age 21

Why was this voyage so important? He came up with the mechanism for evolution

Where did he go on his voyage? He sailed from England to the South Pacific and South America

One special place he traveled to was the Galapagos Islands About 600 miles west of Ecuador

Volcanic ash on an island

What evidence did he find on his voyage that gave him this idea?

Finches (a type of bird) Large ground Finch Medium ground finch Sharp beaked ground finch

Other Finches Cactus Finch Small Tree Finch

What did he learn from the finches? That all the birds were very similar but have slight variation in beak type, size or color. The variations were mostly adaptations specific for the island they lived on.

How did Darwins’ finches evolve? 1.The islands were connected and only one finch existed 2.The islands separated and finches were isolated on separate islands with different environments 3.Over many years, new and different species formed

Pinta Island Intermediate shell Pinta Isabela Island Dome-shaped shell Hood Island Saddle-backed shell Hood Floreana Santa Fe Santa Cruz James Marchena Fernandina Isabela Tower Giant Tortoises of the Galápagos Islands Section 15-1 On the desert-like Hood Island, tortoises had long necks… …while on the lush rainforest of Isabela Island, tortoises had short necks… and on Pinta Island, tortoise necks were somewhere in between

After his voyage, Darwin spent a great deal of time thinking about his findings. He began to wonder if animals living on different islands had once been members of the ____________ that had developed _________ characteristics after becoming _______ from one another in different habitats. same species different isolated Biology by Miller and Levine; Prentice Hall Publishing©2006

The Galάpagos Islands are close together but have very different _______. Some were hot and dry, with little vegetation. Others had more rainfall and were rich in vegetation Each island had its own _____ _________ of plant and animal species. Biology by Miller and Levine; Prentice Hall Publishing©2006 climates assortment unique

What is Natural Selection? 1. Organisms produce more offspring than can survive (Overproduction). 2. There is variation in any population. 3. Variations may lead to survival or death. 4. Those organisms most capable of surviving will reproduce and pass on their genes. (Descent w/ Modification) 5. There is an environmental change. 6. A shift in the gene pool occurs.

Natural Selection—notes! In order to occur, must have: 1.Variation—bell curve; unequal survival rate. Some are better “adapted” to survive. Causes: Reproduction, Mutations, Recombination. 2.Overproduction—exponential growth; more offspring produced than will survive (due to competition).

3. Environmental Change (selective pressure) Selection Pressures: Are living and nonliving factors in the environment that make life “a constant struggle for survival”. These drive the evolution of a species. Selection Pressures determine who lives and who dies. 4. Descent with Modification—Over time, natural selection results in species with adaptations that are best for survival & reproduction.

NATURAL SELECTION - a case study by Peter & Rosemary Grant Medium ground finch of Galapagos Islands off Ecuador [Darwin's Finches*]Darwin's Finches* –lives on seeds, cracks them open via force of beak the Grant's studied finches on Daphne Major, a small island (800 sq. yd) In 1977: Island had only 2mm of rain instead of normal 130mm... drought resulted in a loss of 84% of medium ground finch population –most died of starvation –seeds of Tribulus cistoides, primary food source --> were hard to open unless birds had large, deep beaks, [the survivors had deeper beaks] Natural Selection lead to increase in average beak depth of survivors (graph of data*) graph of data Offspring of survivors in subsequent years had beaks 0.5mm deeper