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December, 1831, the HMS Beagle sailed around the world from England for 5 years. Charles Darwin - 22 yr old - ship’s naturalist, studying the natural world - observed plants & animals, wondered why so different from those in England

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Ch 7, Sec 1 Darwin’s theory

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ch 7 sec 1 darwin s theory

December, 1831, the HMS Beagle sailed around the world from England for 5 years.

Charles Darwin

- 22 yr old

- ship’s naturalist, studying the natural world

- observed plants & animals, wondered why so different from those in England

- observations led to theory of evolution by natural selection

Ch 7, Sec 1 Darwin’s theory

*Darwin’s important observations

- diversity of organisms

- remains of ancient organisms

- characteristics of organisms on Galapagos Islands


- Darwin amazed by diversity of living things he saw;

- Brazil: insects that looked like flowers & ants marched across the forest floor like armies



- group of similar organisms that can mate with each other and produce fertile offspring

- Scientists have ID’d more than 1.7 million species of organisms on Earth


- preserved remains or traces of an organism that lived in the past

- Darwin noted fossil bones that resembled bones of living sloths. Fossil bones were larger than sloths during his time.


Galapagos Organisms

- 1835 Beagle reached Galapagos Islands

- Darwin observed many unusual life forms on the islands

- noted many similarities between Galapagos and South America organisms

- noted many differences between organisms on the islands and the mainland

- iguanas on Islands had large claws to grip slippery rocks

- iguanas on mainland had smaller claws for climbing trees


- Darwin hypothesized

- a small number of different plant and animal species came to Galapagos Islands from mainland; maybe from drifting on a log, blown out to sea during a storm

- comparisons of organisms among Islands

- tortoises on one island had dome-shaped shells (ground food) and on another island the tortoises had saddle-shaped shells (high reaching food). Shell shape based on needs and food available to tortoise.



- a trait that helps an organism survive & reproduce in its environment

- ex: beak shape, milkweed (poisonous plant), bright colors of flowers attract insects & aid in pollinating,

Darwin noticed the finches were different from island to island; most obvious was bird beak shape and size

- finches with narrow, needle-like beaks ate insects

- finches with wide, strong beaks ate seeds


*Darwin reasoned that plants or animals arrived on Galapagos Islands faced environmental factors that were different from those on the mainland. He hypothesized that species gradually changed over many generations and became better adapted to the new environment


- gradual change in a species over time

Selective Breeding

- Darwin studied other examples in living things to help understand how evolution might occur

- English farmers used selective breeding to produce sheep with fine wool, pigeons with more tail feathers

- Darwin wondered if selective breeding happened in nature


1859 Darwin published book “On the Origin of Species by Natural Selection”

- proposed that evolution occurs in nature through a mechanism of natural selection

Natural Selection

- individuals better adapted to their members of their environment are more likely to survive & reproduce than members of the same species

Darwin read “Essay on the Principle of Population” by Thomas Robert Malthus

- Malthus argued that humans and other organisms produce a lot of offspring

- Malthus pointed out that sometimes food supply is not large enough to feed all offspring


Darwin knew that living things needed other resources beside food for survival; water, living space

Genetic Variation

- difference between individuals of the same species

- members of a species differ from one another in many of their traits

- ex: certain insects able to eat foods that other insects of their species avoid, giving the insects an advantage over most insects in their species


- with limited food & resources, members of a species must compete with each other to survive

- does not always involve direct physical fighting, but can also be indirect. Insects unable to find enough food will not survive



- Darwin observed that some variations make individuals better adapted to their environ, more likely to survive & reproduce

- Offspring may inherit helpful characteristics, in turn, more likely to survive & reproduce, passing on characteristics to offspring

*- proposed that, over a long time, natural selection can lead to change. Helpful variations may gradually accumulate in a species, while unfavorable ones may disappear


Environmental Factors

- can affect an organism’s ability to survive and lead to selection

- ex: monkey flowers cannot grow in soil that has high concentration of copper, but because of genetic variation, some monkey flowers now grow near copper mines

Genes & Natural Selection

- like environ. Factors, genetic variation contributes to evolution

- without variations, all members of a species would have the same traits, natural selection would not occur because all individuals would have an equal chance of surviving & reproducing


- variations can result from mutation and shuffling of alleles during meiosis

- genes passed from parents to offspring, only traits inherited or controlled by genes can be acted upon by natural selection