10.2 Darwin’s Observations

KEY CONCEPT

Darwin’s voyage provided insight on evolution.

10.2 Darwin’s Observations

Darwin observed differences among island species.

• Variation is a difference in a physical trait.

– Galápagos tortoises that live in areas with tall plants

have long necks and legs.

– Galápagos finches that live in areas with hard-shelled

nuts have strong beaks.

10.2 Darwin’s Observations

• An adaptations is a feature that allow an organism to better

survive in its environment.

– Species are able to adapt to their

environment.

– Adaptations can lead to genetic

change in a population.

10.2 Darwin’s Observations

• Darwin found fossils of extinct animals that resemble

modern animals.

• Darwin found fossil shells high up in the Andes mountains.

Darwin observed fossil and geologic evidence supporting

an ancient Earth.

10.2 Darwin’s Observations

• He saw land move

from underwater to

above sea level

due to an

earthquake.

• Darwin extended

his observations to

the evolution of

organisms.

10.2 Darwin’s Observations

KEY CONCEPT

Darwin proposed natural selection as a mechanism for

evolution.

10.2 Darwin’s Observations

Several key insights led to Darwin’s idea for natural

selection.

• Darwin noticed a lot of variation in domesticated plants

and animals.

• Artificial selection is the process by which humans

select traits through breeding.

neck feathers

crop

tail feathers

10.2 Darwin’s Observations

• Natural selection is a mechanism by which individuals

that have inherited beneficial adaptations produce more

offspring on average than do other individuals.

• Heritability is the ability of a trait to be passed down.

• There is a struggle for survival due to overpopulation

and limited resources.

• Darwin proposed that adaptations arose over many

generations.

10.2 Darwin’s Observations

• There are four main principles to the theory of natural selection.

– Variation: heritable differences that exist in every population basis for

natural selection.

Natural selection explains how evolution can occur.

– Overproduction: increase chances for survival however

increases competition for resources

– Adaptation: certain variation allows an individual to survive

better. – Descent with modification: natural selection result in

adaptations that will pass on the trait VARIATION OVERPRODUCTION ADAPTATION

• Fitness is the measure of survival ability and ability to

produce more offspring.

DESCENT with

MODIFICATION

10.2 Darwin’s Observations

• Natural selection can act only on traits that already exist.

• Structures take on new functions in addition to their

original function.

Natural selection acts on existing variation.

wrist bone

five digits

10.2 Darwin’s Observations

KEY CONCEPT

Evidence of common ancestry among species comes

from many sources.

10.2 Darwin’s Observations

Evidence for evolution in Darwin’s time came from

several sources.

• Fossils provide evidence of evolution.

• Fossils in older layers are more primitive than

those in the upper layers.

10.2 Darwin’s Observations

• The study of geography provides evidence of evolution.

– island species most closely resemble nearest mainland

species

– populations can show variation from one island to

another

10.2 Darwin’s Observations

• Embryology provides evidence of evolution.

Larva

Adult barnacle Adult crab

– identical larvae, different adult body forms

– similar embryos, diverse organisms

– Distant common ancestor

10.2 Darwin’s Observations

• The study of anatomy provides evidence of evolution.

Human hand Bat wing Mole foot

– Homologous structures are similar in structure but

different in function.

– Homologous structures are evidence of a common

ancestor.

10.2 Darwin’s Observations

• Vestigial structures are remnants of organs or structures

that had a function in an early ancestor.

• Ostrich wings are examples of vestigial structures.

Structural patterns are clues to the history of a species.

10.2 Darwin’s Observations

Human hand

Bat wing

Mole foot

Fly wing

– Analogous structures are not evidence of a common

ancestor.

• The study of anatomy provides evidence of evolution.

– Analogous structures have a similar function.

10.2 Darwin’s Observations

KEY CONCEPT

New technology is furthering our understanding of

evolution.

10.2 Darwin’s Observations

Fossils provide a record of evolution.

• Paleontology is the study of fossils or extinct organisms.

10.2 Darwin’s Observations

• Paleontology provides evidence to support evolution.

10.2 Darwin’s Observations

Molecular and genetic evidence support fossil and

anatomical evidence.

• Two closely-related organisms will have similar DNA

sequences.

10.2 Darwin’s Observations

• Pseudogenes are sequences providing evidence of

evolution. Similar to vestigial structures.

– no longer function

– carried along with functional DNA

– can be clues to a common ancestor

10.2 Darwin’s Observations

• Hox genes indicate a very distant common ancestor.

– control the development of specific structures

– found in many organisms

• Protein comparisons, or molecular fingerprinting reveals

similarities among cell types of different organisms. Cells

from different species that have the same proteins most

likely come from common ancestor.

10.2 Darwin’s Observations

• Scientist from any fields contribute to the understanding

of evolution.

• The basic principles of evolution are used in many

scientific fields.

Evolution unites all fields of biology.