Darwin’s Observations

The Theory of Evolution by Natural Selection

The HMS Beagle

• Charles Darwin embarked on the second voyage of the HMS Beagle on December 27,1831, on a survey expedition under the command of Captain Robert Fitzroy.

• The main purpose of the expedition was to map out the southern coast of South America, and Darwin was on board as a geologist, to collect specimens.

The HMS Beagle (cont’d)

• The journey was supposed to last 2 years, but the ship returned to England on October 2, 1836, almost 5 years after its departure.

What Darwin Saw

• Similar flora & fauna (plants & animals) on the Galapagos as on mainland South America

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

What Darwin Saw (cont’d)

• Many species of finches and mockingbirds

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.QuickTime™ and a

TIFF (Uncompressed) decompressorare needed to see this picture.

Other observations…

• The fossil record: – Glyptodon (like the armadillo)– Megatherium (like the sloth)

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Other observations (cont’d)

• Comparative anatomy of animals:– Homologous features:

Other observations (cont’d)

• Comparative anatomy of animals:– Analogous features:

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Other observations (cont’d)

• Comparative anatomy of animals:– Vestigial features:

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Other observations (cont’d)

• Investigated mechanisms of artificial selection (pigeon breeding, etc.)

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Other observations (cont’d)

• Thomas Malthus, Essay on the Principle of Population (1798)

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

The Theory of Evolution by Natural Selection

• Observation 1: Individuals within a species vary in many ways.

• Observation 2: Some of this variability can be inherited.

• Observation 3: Every generation produces far more offspring that can survive and pass on their variations.

• Observation 4: Populations of species tend to remain stable in size.

The Theory of Evolution by Natural Selection

• Inference 1: Members of the same species compete with each other for survival.

• Inference 2: Individuals with more favourable variations are more likely to survive and pass them on. Survival is not random.

• Inference 3: As these individuals contribute proportionally more offspring to succeeding generations, the favourable variations will become more common. (This is natural selection.)