Ch. 15: Evolution Charles Darwin – 1831- Sailed around the world Collected plants and animals at every stop. Noted similarities and differences among the finches and tortoises on the Galapagos Islands with those in S. America. Hypothesized the animals adapted to local conditions on the islands after their arrival.

Pinta Island Intermediate Shell Hood Island Saddle-backed shell Isabela Island Dome-shaped shell

Proposed his theory of evolution: change over time Important note: A scientific theory is a well-supported scientific explanation based on measureable events in the natural world. Darwin published his book, On the Origin of Species, in 1859.

Darwin’s Observations 1. Patterns of Diversity –wondered why different continents with similar habitats had very different animals. Examples: Why were there no rabbits in Australia or kangaroos in Europe?

2. Living Organisms and Fossils – Why were so many species extinct and why do they seem related to living species?

3. The Galápagos Islands – The islands were close together, yet each had different climates. As a result, each island had its own unique animal life, such as tortoises, finches, etc.

Influences on Darwin Jean Baptiste De LaMarck proposed first hypothesis of evolution (1809). 1. “Tendency toward perfection” – Organisms “willed” themselves to change by using or not using certain body parts. 2. “Use or disuse” – Organisms acquired traits during their life by the use or disuse of organs. These new traits could then be passed on to offspring. 3. “Inheritance of acquired traits” –Traits acquired during life were passed on to offspring.

LaMarck’s ideas turned out to be wrong, but he was the first to propose a testable means by which evolutionary change could occur. It just turned out that when his ideas were tested experimentally, the results disproved his hypothesis.

Thomas Malthus Human population will grow unchecked, there would be insufficient living space and food. Believed only forces that worked against growth were war, famine, and disease.

James Hutton and Charles Lyell were early geologists who helped scientists realize that Earth is millions of years old, and the processes that changed Earth in the past are the same processes that operate in the present.

Natural Selection 1. Heritable variation: differences in traits among a population of organisms are passed from parent to offspring. Plant and animal breeders use heritable variations to improve crops and livestock by choosing to breed those organisms that have the traits they want It is nature that provides the variation; humans select the variations they find most useful This is artificial selection

Darwin’s ideas of evolution centered on: Natural Selection - 2. “Struggle for existence” More offspring are born than can survive. Organisms must compete to survive & reproduce. Food, living space, mates, and other necessities must all be competed for 3. “Survival of the Fittest”: the ability to survive and reproduce. .

Adaptation: any inherited trait that aids survival. Over time, natural selection causes changes in the traits of a population. Adaptations can be anatomical, functional (physiological) or behavioral. Successful adaptations allow an organism to become better suited to their environment. Those with the best traits survive to reproduce and pass on those desirable traits.

Descent with modification – offspring vary from the parents Over time species of today look different from their ancestors It also implies “common ancestry” – similar organisms have similar traits because they were inherited from a common ancestor.

Evidence of Evolution comes from: 1) Fossil Record shows groups of plants and animals being replaced by other types over time. Most often, major changes come after mass extinction events. Darwin argues this showed living things had been evolving on Earth for millions of years.

Scientists today call this biogeography NA wolf European Fox Australian Dingo SA wolf African hyena 2) Geographic Distribution of Living Species-Darwin found different animals on different continents that had similar anatomies and behaviors. These animals were living under similar ecological conditions and were exposed to similar pressures of natural selection. They ended up evolving certain features in common. Scientists today call this biogeography

3) Homologous structures – common structures are inherited from common ancestors. Example: Limb bone patterns in all vertebrate animals can be traced back to Lobe-finned fish of 350 million years ago.

Alligator Bird Mammal Turtle Ancient lobe-finned fish

Vestigial Structures – Features that are reduced or useless, but functional in far distant ancestors. It infers evolutionary change. Examples: tiny leg bones and hipbones in pythons; hip bones in whales

Python “toes”

Hind-limb bones from a whale on display in the Zoology Museum at Aberdeen, England.

4) Embryology – vertebrate embryos repeat the major evolutionary features of ancestral embryos during development. The same groups of embryonic cells develop in the same order and in similar patterns to produce the tissues and organs of all vertebrates. Example: At early stages of development, all vertebrate produce tails, gill pouches, successive chamber growth of the heart, etc.

A B C

A- human C-Chicken B- spotted dolphin