Darwin

For centuries, Europeans believed that God created all plants and animals in seven days in 4004 BC.
The prevailing view was that organisms had hardly changed from their divine designs.

Proposed that all organisms are connected through a "fountain of life."
Suggested that everything evolved from primitive worms.
Developed the theory of inheritance of acquired characteristics, where changes in an individual's characteristics over its lifetime could be passed to offspring.

Example: Giraffes' necks lengthen due to stretching for leaves, which could then be inherited.
It is now understood that body changes during an individual's life do not alter the genes.
Experiences show that parents do not necessarily transmit acquired characteristics to their offspring (e.g., big muscles).

In 1831, Charles Darwin started a 5-year voyage as the official naturalist on HMS Beagle.

One of the notable locations Darwin visited was the Galapagos Islands off the coast of Ecuador:
- Locations within Galapagos: Fernandina, Santiago, Isabela, Floreana, Santa Cruz, Santa Fe, San Cristobal, Espanola.
- The Galapagos Islands are volcanic and initially devoid of native plants or animals; they became colonized over time.

The term "Galapagos" means "tortoise."
Darwin noted that, without competition, tortoises developed into giant forms, unique to each island.
Example: Tortoises on drier islands had smaller, saddled-back shells and longer necks.

Darwin observed various types of finches on the Galapagos Islands, which were not found on the mainland.
Each finch type was specialized to exploit different habitats and had distinct bills.
Hypothesized that a mainland bird evolved into multiple forms to adapt to the varying environments on the islands.

Finches migrate between North and South America; however, some are diverted by the Humboldt Current, landing on diverse islands with varying food sources.
Only finches adapted to the specific food sources on each island survived.

After his expeditions, Darwin settled at Down House, Kent, to analyze his specimens and continue his research.

Darwin dedicated years at Down House gathering evidence for his theory, including extensive studies of barnacles and conducting breeding experiments with fancy strains of pigeons.
Quote: "Although man does not cause variability and cannot even prevent it, he can select, preserve, and accumulate the variations given to him by the hand of nature in any way which he chooses; and thus he can certainly produce a great result."

A naturalist who conducted a significant fieldwork in Amazonia and the East Indies.
Independently developed the theory of natural selection while suffering from fever on the island of Helmahera in 1858.
Wrote a 9-page letter outlining the theory to Darwin, which led to a joint publication.

The primary flaw in Darwin's theory was his inability to explain the mechanism of evolution.
He understood the potential controversy and thus delayed publication from 1837 until 1858.

Observations:
- Organisms adapt to their environments.
- Variation exists within species.
- Offspring inherit characteristics from parents.
- Organisms can produce large numbers of offspring.
- Populations remain relatively stable over time.
Conclusions:
- Struggles for survival exist.
- Some variations are better suited to environments.
- Better-adapted organisms survive and pass on traits.
- Over time, changes in alleles may lead to new species.

In a beetle population, green and red varieties exist.
Birds preferentially feed on the red variety, leading to more green beetles surviving and reproducing, which alters the gene pool over generations.

Within giraffe populations, some individuals are born with longer necks.
Over many generations, these longer-necked individuals are favored, survive better, reproduce more successfully, and pass their traits to the next generation.