Ch 15 Evolution

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15.1 Evolution: how modern organisms have descended from ancient organisms

Voyage of the Beagle:

Darwin went on a 5-year voyage around the world

collected and studied plant and animal specimens

his observations led him to believing that life changes over time

Darwin's Observations:

collected fossils - some resembled present organisms, while others looked unalike

Galapagos islands were close together, but had very different climates

finch and tortoise - characteristics varied

wondered if animals living on different islands had once been same species >> would've evolved from an original SA species

15.2 Ideas that Shaped Darwin's thinking

Hutton: proposed that Earth had to be much more than a few thousand years old

Lyell: geological features could be built up or torn down over long periods of time >> if Earth could change over time, life might change as well

Lamarck: proposed organisms could alter the size or shape of particular organs by using their bodies in new ways >> incorrect

Didn't know: how traits are inherited & that behavior has no effect on heritable characteristics

Malthus: babies were being born a lot faster than people were dying >> if human populations grew unchecked, there'd be insufficient living space and food for everyone

Darwin connected this to plants & animals: if all offspring survived of almost any species for several generations, they would overrun the world

15.3 Artificial Selection: selection by humans for breeding useful traits among different organisms

Struggle for Existence: members of each species compete regularly to obtain food, living space, and other life necessities

Survival of the Fittest:

fitness is result of adaptations

successful adaptations enable organisms to be better suited to their environment (better suited=reproduce most successfully)

also known as natural selection

Descent With Modification:

each species has descended, with changes, from other species over time

implies all living things are related to one another

What Evidence of Evolution Did Darwin Present?

fossil evidence

geographical distribution of living species

homologous structures

similarities in early development or embryology: early stages of many animals with backbones are very similar

*** individual organisms differ, and some of this variation is heritable

16.1 Genetic Variation is studied in populations

Gene Pool: consists of all genes and alleles that are present in a population

Relative Frequency of an Allele: number of times allele occurs in a gene pool (%)

Main Sources of Genetic Variation:

mutations - point or chromosomal change in DNA sequence

occur from... mistakes in DNA replication, radiation, chemicals

genetic shuffling due to sexual reproduction