Scientists have identified more than 1.7 million species of organisms on earth
Species - group of similar organisms that can mate with each other and produce fertile offspring
Fossils
Fossil - preserved remains or traces of an organsim that lived in the past
darwin discovered bones of a sloth that wree much larger than those of the sloths that he observed that were alive
Galapagos Organisms
Comparisions to South American Organisms
galapagos iguanas had larger claws that allowed them to grip slippery rocks to eat seaweed
mainland iguanas had smaller claws that allowed them to climb trees to eat the leaves
darwin hypothesized that some plants and animals on the islands came from the mainland and eventually their offspring became different from their mainland relatives
Comparisons Amoung the Islands
darwin noticed differences between organisms on different islands
the tortoises on one island had dome-shaped shells while thoses on other islands had saddle-shaped shells
Adaptations
it was observed that the finches across all of the islands had varying beak sizes, each species was well suited to the life it lead
finches that at inscets had narrow beaks
finches that ate seads had strong wide beaks
Adaptation - a trait that helps an organism survive and reproduce
Evolution p.g. 142
Darwins Reasoning p.g. 142
darwin reasoned that plants and animals on the islands faced conditions that were different from those on the mainland. Darwin hypothisized that species gradually changed over many generations and became better adapted to new conditions
evolution - gradual change of a species over time
scientific theory - a well tested concept that explains a wide range of observations
Selective Breeding p.g. 142
Darwin thought that a process similar to slective breeding was happening in nature
Natural Selection p.g.143 - 145
in his book, Origin of Species, darwin proposed that evolution occurs by means of natural selection
natural selection - process by which individuals that are better adapted to their environment are more likely to survive and reproduce than other member of the same species
factors that affect natural selection include overproduction, competition, and variations
Overproduction p.g. 143
if too many offspring are produced there cannot be enough resources - water, food, space, etc - for all of them to survive
variations p.g. 143
variation - any difference between individuals of the same species
competition p.g. 144
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Darwin's Theory