Chapter 21 Flashcards
Beaks of Darwin’s Finches
Darwin collected 31 specimens from 3 islands in the Galápagos Islands
Darwin not an expert on birds.
Took them back to England for identification.
Told his collection was a closely related group of distinct species.
All were similar except for beak characteristics.
In all, 14 species now recognized.
3 conditions of natural selection
Phenotypic variation must exist in the population.
This variation must lead to differences among individuals in lifetime reproductive success.
Phenotypic variation among individuals must be genetically transmissible to the next generation.
Peter and Rosemary Grant
Studied medium ground finch on island called Daphne Major
Found beak depth variation among members of the population
Industrial melanism
Phenomenon in which darker individuals come to predominate over lighter ones
Artificial Selection
Change initiated by humans
Experimental selection
Scientists have imposed selection
Agricultural selection
Differences have resulted from generations of human selection for desirable traits, such as greater milk production and larger corn ear size
Domestication
Human-imposed selection has produced a variety of cats, dogs, pigeons, and others
Fossil Evidence of Evolution
Fossils are the preserved remains of once-living organisms
Rock fossils are created when three events occur
Organism buried in sediment.
Calcium in bone or other hard tissue mineralizes.
Surrounding sediment hardens to form rock.
Estimating the age of fossils
In Darwin’s day, rocks were dated by position relative to one another
Today geologists determine the absolute age of rocks using isotopic dating
Evolutionary transitions
gaps in the fossil record
Homologous structures
Structures with different appearances and functions that all derived from the same body part in a common ancestor.
Early embryonic development
Strongest anatomical evidence supporting evolution comes from comparisons of how organisms develop
Embryos of different types of vertebrates, for example, often are similar early on, but become more different as they develop
Imperfections
some organisms do not appear perfectly adapted
Pseudogenes
Fossil genes; traces of previously functioning genes
Vestigial structures
Vestigial structures have no apparent function, but resemble structures ancestors possessed
Biogeography
Study of the geographic distribution of species
Convergent evolution
Similar forms having evolved in different, isolated areas because of similar selective pressures in similar environments
Darwin noted on his voyage that
Islands are often missing plants and animals common on continents.
Can live there if introduced
Species present on islands often diverged from continental relatives.
Occupy niches used by other species on continents
Island species usually are more closely related to species on nearby continents.
Darwin’s Critics 7 principal objections
“Evolution is not solidly demonstrated”
“There are no fossil intermediates”
The intelligent design argument
“Evolution violates the Second Law of Thermodynamics”
“Proteins are too improbable”
“Natural selection cannot explain major changes”
The irreducible complexity argument
