Natural Selection – Part 3

OnlineHS: Biology A

The Galapagos Islands

• The Galapagos islands were pushed up from the floor of the Pacific Ocean as volcanoes more than 1 million years ago.

• They are 600 miles west of Ecuador, in South America.

Lessons from the Galapagos: Finches

• On these islands, Darwin found 14 species of finches, occupying different habitats, and with different diets.

• The species were all approximately the same size, shape and color. The biggest difference was their beaks.

• Some have long, thin woodpecker-like beaks and eat insects under tree bark.

• Some have beaks like sparrows (short and wide) and feed on small seeds.

• Some have beaks that are curved and sharp and eat buds and fruits.

• These finches cannot fly far, and do not migrate.

Tree Finches & Ground Finches

• It was hypothesized that they were all descendants of one species of finch that had made its way to the islands many years ago, and speciation occurred as a way of lessening competition for the scant resources found on the islands.

Speciation Example: Finches

• 14 different species of Finch were found on the Galapagos Islands that looked very closely related in size and coloration.

• The major difference was the size of their beaks.

• It is proposed that due to natural selection pressures one species of Finch gradually developed into 14 different species .

Galapagos: Tortoise

• In addition to the finches, the islands were populated by Giant Tortoises.

• Each kind of tortoise had a different pattern on its shell.

• Each kind lived on a different island.

Which one of Darwin’s Main Points do the following pictures

show?

OverproductionCompetitionVariationAdaptationNat. SelectionInheritanceSpeciation

Which one of Darwin’s Main Points?

• Competition

Which one of Darwin’s Main Points?

• Variation

Which one of Darwin’s Main Points?

• Adaptation

Which one of Darwin’s Main Points?

• NaturalSelection

Which one of Darwin’s Main Points?

• Adaptation

Which one of Darwin’s Main Points?

• Is this speciation orvariation?

• Why or why not?

Which one of Darwin’s Main Points?

• Inheritance(dark haired parents, light/red hair baby)

Which one of Darwin’s Main Points?

• Speciation

500,000 years

Charles Darwin (1809-1882)

• Descent with Modification: – All organisms on earth are

related through some unknown ancestral type that lived long ago.

• Natural selection is the mechanism by which species evolve or change over (geologic) time.

Theory of Evolution

• Darwin’s work led up to the current Theory of Evolution.

• Did Darwin “discover” the Theory of Evolution? (no)

• The great diversity of life on earth is the result of over 3.5 billion years of very slow gradual change (evolution) in the DNA of organisms.

• Every available space on earth is filled with life forms.

The “Darwin Finches”

• Darwin did not mention the finches in his book The Origin of Species. They only appear in his Journal, being mentioned only in passing in the first edition (1839), and then having a few paragraphs and a picture six years later in the revised edition (1845).

• Darwin speculated that the different finches had descended from a common ancestor and had changed to be able to do different things. He was never sure that the different species were from different islands.

• They were never known as "Darwin's Finches" until 1936, and the name was popularized by ornithologist David Lack in his book Darwin's Finches (1947).

• Though the finches were not important in the work of Charles Darwin, they do tell us something about evolution.

• Variation in a species is a good thing, as it gives them the ability to cope with environmental change, but variation does have limits.

Clearing-up Science Myth:

Darwin’s Place In Science

Important point: • ALL of the branches of

science that have worked to find answers to questions about the natural world since Darwin’s time have lent support to his ideas.

Questions to Consider Copy these into your journal and answer them

• Is it possible to adapt to a new environment in one’s lifetime?

• Is that evolution? • Is it possible to physically pass on those new

adaptations to your offspring?• Is evolution only about the distant past, or is

it still happening today?