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Organic molecules, bipolymers, systems of chemical reactions
Evidence comes from
chemical analysis and measurements of radioactive elements in primitive rocks and fossils
Lab experiments that show how simple inorganic compounds might have reacted to produce amino acids, sugars, and other organic molecules that became the building blocks for proteins, carbohydrates, RNA and DNA.
Moved from single-celled bacteria to multi-cellular protists, plants, fungi, and animals.
This phase is ongoing.
Fig. 4-2, p. 84 Variety of multicellular organisms form, first in the seas and later on land Biological Evolution (3.7 billion years) Chemical Evolution (1 billion years) Formation of the earth’s early crust and atmosphere Small organic molecules form in the seas Large organic molecules (biopolymers) form in the seas First protocells form in the seas Single-cell prokaryotes form in the seas Single-cell eukaryotes form in the seas
Fig. 4-3, p. 84 Modern humans appear about 2 seconds before midnight Recorded human history begins about 1/4 second before midnight Origin of life (3.6-3.8 billion years ago) Age of mammals Age of reptiles Insects and amphibians invade the land First fossil record of animals Plants begin invading land Evolution and expansion of life
“ Can we doubt…that individuals having any advantage, however slight, over others would have the best chance of surviving and of procreating their kind? On the other hand, we may feel sure that any variation in the least degree injurious would be rigidly destroyed. This preservation of favorable variations, I call Natural Selection.”
Natural selection is the process by which individuals that have favorable variations and are better adapted to their environment survive and reproduce more successfully than less well adapted individuals do.
Darwin proposed that over many generations, natural selection causes the characteristics of populations to change.
Evolution is a change in the characteristics of a population from one generation to the next.
Even when a favorable genetic trait is present in a population, most of the population would have to die or become sterile so individuals with the trait can become dominant and pass the trait on through natural selection.
Most members of the human population would have to die prematurely for hundreds of thousands of generations in order for a new genetic trait to dominate.