The basic idea of biological evolution is that the earth's present-day species are descended from earlier, distinctly different species.
Learning Goal 2
Molecular evidence substantiates the anatomical evidence for evolution and provides additional detail about the sequence in which various lines of descent branched off from one another.
Learning Goal 3
Natural selection provides the following mechanism for evolution: Some variation in heritable characteristics exists within every species; some of these characteristics give individuals an advantage over others in surviving and reproducing; and the advantaged offspring, in turn, are more likely than others to survive and reproduce. As a result, the proportion of individuals that have advantageous characteristics will increase.
Learning Goal 4a
Heritable characteristics can be observed at molecular and whole-organism levels—in structure, chemistry, or behavior.
Learning Goal 4b
Heritable characteristics influence how likely an organism is to survive and reproduce.
Learning Goal 5
New heritable characteristics can result from new combinations of existing genes or from mutations of genes in reproductive cells. Changes in other cells of an organism cannot be passed on to the next generation.
Learning Goal 6a
Natural selection leads to organisms that are well-suited for survival in particular environments.
Learning Goal 6b
Chance alone can result in the persistence of some heritable characteristics having no survival or reproductive advantage or disadvantage for the organism.
Learning Goal 6c
When an environment, including other organisms that inhabit it changes, the survival value of inherited characteristics may change.
Learning Goal 7
Modern ideas about evolution and heredity provide a scientific explanation for the history of life on Earth as depicted in the fossil record and in the similarities evident within the diversity of existing organisms.
Learning Goal 8
Life on earth is thought to have begun as simple, one-celled organisms about four billion years ago. Once cells with nuclei developed about a billion years ago, increasingly complex multi-cellular organisms evolved.
Learning Goal 9
Evolution builds on what already exists, so the more variety there is, the more there can be in the future. But evolution does not necessitate long-term progress in some set direction. Evolutionary change appears to be like the growth of a bush: Some branches survive from the beginning with little or no change; many die out altogether; and others branch repeatedly, sometimes giving rise to more complex organisms.
Learning Goal 10
The continuing operation of natural selection on new characteristics and in diverse and changing environments, over and over again for millions of years, has produced a succession of diverse new species.