Evolution Chapter 6

Pre-Darwinian Theories

Darwin’s Voyage  Where did he go and why?  5 year trip around the world on the HMS Beagle in 1831  To learn about living things as the ship’s naturalist  Saw many living things different from life in England

H.M.S. Beagle

A Brief Biography of Charles Darwin

Darwin's Observations  Amazed by the diversity of life  Large sloth & armadillo bones in Argentina  Diversity in the Galapagos Islands  Species: a group of similar organisms that can mate with each other and produce fertile offspring

Similarities and Differences  How did Darwin think plants and animals had originally come to the Galapagos Islands? He inferred:  Blown out to sea during a storm  Adrift on a fallen log  Reached the islands, reproduced  Offspring eventually became different from mainland species  Species differed island to island

Adaptations  Adaptation: a trait that helps an organism survive and reproduce  Tortoises’ shells  Finch beaks  Adaptations are controlled by genes!

Disney Imagineering Take Some Notes About Animal Adaptations That help Them Communicate! Specifically: Elephants Dolphins Naked Mole Rats Meerkats For Example: WITH NO THUMBS YOU COULDN’T….

Adaptations

New Adaptation?

Nothing Works All The Time!

Darwin’s “Dangerous” Idea  Perhaps the species became better adapted to the new conditions  He did not know how it happened  Thought it might be similar to selective breeding  evolution: gradual change in a species over time

Artificial Selection “Selective Breeding”

Artificial Selection Myth? Samurai crab, H. japonica and stylized Kabuki samurai face

Natural Selection  Explanation proposed by Darwin and Alfred Russel Wallace about how evolution occurs  Process by which individuals better adapted to environment are more likely to survive & reproduce  Factors: overproduction – competition – variations - selection

Overproduction  Most species produce more offspring that can survive  Not enough resources available for all: food; water; space  Ex: sea turtles – many are born but few survive  Darwin wondered why?????

Adult female Sea Turtles return to the beach where they were born to lay up to 200 soft-shelled eggs in the sand. When the baby turtles hatch, they immediately head for the nearby water. Many young turtles are eaten by birds and other predators during this difficult trip. It has been estimated that only 1% of these hatchlings will reach adulthood. No one knows how the females find the beach where they were born.

Variations  Difference between individuals of same species  Genetic!  EX: some turtles are faster than others  Could help them survive

Happy Face Spiders look different, but can interbreed they are the same species: Theridion grallator. Variations in the Species!

Adaptation/Competition  Indirectly for available resources  Not usually physical  Ex: some turtles don’t find food  Some don’t escape predators

Selection  Some variations = better adapted  More likely to reproduce  Offspring may inherit helpful alleles  More individuals have trait after many generations  ENVIRONMENT does the “selecting”  Natural selection can lead to evolution over a long period of time  Ex: many faster turtles

Natural Selection

The Role of Genes in Evolution  Darwin knew nothing of genes or mutations  He could not explain how traits were passed on  Now: Only inherited traits are acted upon by natural selection

Evolution in Action  1977 study on Daphne Major  Little rain led to fewer plants  Fewer plants = fewer seeds  Finches ate large, tough seed pods  Many small-beaked finches did not survive drought  Next year = more finches with larger, stronger beaks

Evolution in Action  Peppered moths of England

How Do New Species Form?  Geographic isolation  A group of individuals remains isolated long enough to evolve different traits  Ex: Kaibab & Abert squirrels

Kaibab Squirrel Abert Squirrel The Kaibab squirrel is isolated in the Kaibab Plateau. South of the canyon and elsewhere, the similar Albert squirrels may be found.

How Do New Species Form? isolation = when some members of a species are cut off from the others a new species can form when a group of individuals remains separated from the rest of his species long enough to evolve different traits

How Do New Species Form?

Continental Drift  As continents separated species became isolated  Began to evolve independently  Australia and the marsupials and monotremes ContinentalContinental Drift

Pangea Pangaea & Continental Drift