1. and the people who influenced Darwin’s thinking
Darwin’s Voyage of Discovery
and the people who influenced Darwin’s thinking

2. Darwin’s Contribution to Science
Charles Darwin,
Darwin was born on February 12, – the same day as Abraham Lincoln.
Darwin developed a scientific theory of biological evolution that explains how modern organisms evolved over long periods of time through descent from common ancestors.

3. Darwin’s Epic Journey
In 1831, Darwin began his five-year voyage on the HMS Beagle.

4. Observations Aboard the HMS Beagle
As he traveled, Darwin noticed three distinctive patterns of biological diversity:
Species vary globally,
Species vary locally, and
Species vary over time.

5. Species Vary Globally
Similar biomes around the world have different species with similar traits.
E.g., ratites, the flightless birds: rheas in grasslands of South America, ostriches in savannas of Africa, and emus in Australian grasslands.

6. Ratites rhea emu ostrich
Species vary globally: Similar animals live in similar habitats in different parts of the world.

7. Species Vary Locally
Different, but related, animal species often occupy different habitats with a local area.
E.g., The two South American species of rheas live in somewhat different environments; one in Argentina’s grasslands and the other in the colder, harsher scrubland to the south.
Greater Rhea, Rhea americana
Lesser Rhea, Pterocnemia pennata

8. Species Vary Over Time
Darwin collected fossils in addition to living specimens.
He noticed that some fossils of extinct animals are similar to extant (living) species.

9. Ideas That Shaped Darwin’s Thinking
Most Europeans in Darwin’s day believed Earth was only a few thousand years.
Geologists James Hutton (1785) and Charles Lyell (1830) published works that stated that Earth is extremely old and the processes that changed the Earth in the past are the same processes that operate in the present.

10. Hutton and Geological Change
Hutton recognized the connections between geological processes and geological features.
Realized that some rocks are formed from molten lava and that others are formed slowly as sediments build up and are put under pressure.
He stated that forces beneath Earth’s surface can build mountain ranges, and mountain ranges can be broken down by rain, wind, heat, and cold.
Believed Earth must be very old for mountains to form or erode away.
James Hutton,

11. Lyell’s Principles of Geology
Hutton strongly influenced Lyell.
Lyell developed the principle of uniformitarianism.
Principle of Uniformitarianism: laws of nature are constant; the geological processes we see in action today are the same ones that shaped Earth millions of years ago.
Agreed with Hutton that Earth must be very old in order for a river to carve out a valley or canyon.
Sir Charles Lyell,

12. Influence of Lyell on Darwin
Darwin read Lyell’s book while he was serving as ship naturalist on the HMS Beagle.
Darwin observed marine fossils in mountains thousands of feet above sea level.
He was in an earthquake that threw him to the ground and lifted a stretch of rocky shoreline >3 m above sea level.
Darwin connected geological ideas with biological ones – If Earth can change over time, it is possible that life can change over time too.

13. Lamarck’s Evolutionary Hypotheses
Darwin was not the first to suggest that evolution had taken place among living organisms.
In 1809, Jean-Baptiste Lamarck suggested that organisms could change during their lifetimes by selectively using or not using various parts of their body.
Lamarck also erroneously stated that individuals could pass these acquired traits on to their offspring, enabling species to change over time.
Lamarck’s theory was quickly discredited.

14. Malthus’ Influence on Darwin
In 1798, the Reverend Thomas Malthus noted that, in London, humans were being born faster than people were dying, causing overcrowding.
If the population kept growing, there would not be enough living space and food for everyone.
However, “misery and vice” kept human population size in check.
Malthus identified “misery and vice” as war, famine, disease, murder and theft, among other factors.

16. Malthus’ Influence on Darwin
Darwin extended Malthus’ reasoning to all living things.
Why was this realization so important?
Darwin was convinced that species evolved, but he did not have a mechanism (a scientific explanation based on a natural process) to explain how and why.
When Darwin realized that most offspring don’t survive and reproduce, he thought about which individuals survive… and why.

17. Artificial Selection (or Selective Breeding)
To find a explanation for change in nature, Darwin studied change produced by plant and animal breeders.
Breeders chose animals to mate that have desirable traits; e.g., plants that bear larger fruit than average or cows that give more milk than others.
Darwin realized this meant that variations could be passed from parent to offspring.
Darwin coined the term “artificial selection.”

18. Artificial Selection
In artificial selection, nature provides the variations, and humans select those they find most useful.
Darwin tested artificial selection by raising and breeding plants and fancy pigeon varieties.
Origin of various varieties of pigeons from the rock pigeon by artificial selection.

19. Darwin’s Theory of Evolution by Natural Selection
Darwin worked out the main points of his theory soon after reading Malthus and thinking about artificial selection.
He did not publish for 20 years because he knew his ideas were “radical” and he didn’t want to be ridiculed like Lamarck had been – he wanted to gather as much evidence supporting his theory as possible before presenting to the public.

20. Darwin’s Theory of Evolution by Natural Selection
In 1858, Darwin reviewed an essay by Alfred Russel Wallace, whose ideas paralleled his own.
Wallace’s essay and Darwin’s observations were presented together at a scientific meeting in 1858.
In 1859, Darwin published On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life.

21. Darwin’s Theory of Evolution by Natural Selection
Darwin’s Observations
Variation: No two individuals are exactly alike.
An heritable trait that increases an organism’s ability to survive and reproduce in its environment is called an adaptation.
Adaptations may be physical (e.g., claws, camouflage coloring), physiological (e.g., photosynthesis), or behavioral (e.g., prey avoidance strategies).
Inheritance: These variations are, in large part, inherited from parents.

22. Darwin’s Theory of Evolution by Natural Selection
Darwin’s Observations
Overproduction: Two parents usually produce more than two offspring (in many cases, many, many more).
Competition: Once the population is large enough, there will be competition for needed resources.
Darwin called this “the struggle for existence.”

23. Darwin’s Theory of Evolution by Natural Selection
Darwin’s Inferences
Natural Selection: Individuals with inherited variations that make them well-adapted for survival in their environment are most likely to live and reproduce, passing their desirable traits on to their offspring.
Darwin called this “survival of the fittest.”
Survival is more than just staying alive; it means reproducing and passing adaptations to the next generation.
Individual variations affect an individual’s relative fitness.
Fitness describes how well an organism can survive and reproduce in its environment.

24. Natural Selection Natural selection occurs whenever –
more individuals are born than can survive (the struggle for existence),
there is natural heritable variation (variation and adaptation), and
there is variable fitness among individuals (survival of the fittest).
From generation to generation, populations continue to change as they become better adapted, or as their environment changes.

26. Darwin’s Theory of Evolution by Natural Selection
Darwin’s Inferences
Speciation: If a population becomes reproductively isolated from some of its members (i.e., members from two groups of the same species are not exchanging genes), then over time, the two groups may change so much that they are no longer able to mate with each other – resulting in the formation of a new species.
reproductive isolation: when gene flow (exchange of genes/alleles) does not occur between two populations of the same species.

27. Remember! Individuals do not evolve, populations do.
You cannot change the genes you have when you are born.
Nature “selects” the individuals that will survive and pass on their traits to offspring.
Over time, the gene variations (or alleles) of the population may change, especially when environmental conditions change.
Change occurs when individuals with a particular trait survive and reproduce and individuals lacking that trait do not survive.

28. Common Descent
Darwin proposed that living species are descended, with modification, from common ancestors – an idea called descent with modification.
This is how Hutton and Lyell influenced Darwin – common descent implies that life has been on Earth for a very long time, enough time for descent with modification to occur.

29. Common Descent
According to the principle of common descent, all species – living and extinct – are descended from ancient common ancestors.