Species Species: group of organisms that can interbreed and produce fertile offspring – Different species rarely breed – Interspecies (between different species) breeding often results in sterile offspring Ex: Horse x Donkey = Mule Ex: Lion x Tiger = Liger – When new species? No longer able to reproduce successfully

Acquired Inheritance: Early idea where organisms could acquire and pass on traits after birth. Early Belief: Giraffes got long neck by stretching Problem: Traits acquired after fertilization cannot be passed to offspring.

Geologic Change Early belief: – Earth ~6,000 years old Rejected by Buffon & Lyell – Life remained unchanged “New” Observations – Rock layers (strata) contained differing fossils – Deeper fossils (older) less complex – Environments changes as continents drift – Environmental changes thought to affect characteristics of organisms – Uniformitarianism: geologic processes that shape earth are uniform and constantly happening

Charles Darwin Observed: – Organisms have variations based upon environment – Similarities between extinct fossils & modern life – Marine fossils atop mountains Natural Selection: Process where organisms with favorable traits survive and reproduce Major concept in biology published in The Origin of Species (1859)

Finches are another example. – Finches with strong, thick beaks live in areas with a lot of large, hard shell nuts. – Finches with delicate beaks live in areas where small insects and fruits are readily available.

Adaptation & Variation Variation: Inherited traits that make an individual different from others – Green, flat wings of the insect above Adaptation: Variation increases the chance of survival – Ability to blend with environment

1)When are two organisms considered a different species? 2)Even though incorrect, why is Lamarck’s theory still relevant? 3)How can the general age of rocks (and fossils) be determined? 4)How does a variation and adaptation differ? 5)What observations did Darwin make regarding the Galapagos’ tortoises and their environment? 6)What is natural selection? REVIEW