Evolution of the Motorcycle
Darwin observed differences among island species.
1. Variation is a difference in a physical trait.
a. Galápagos tortoises that live in areas w/ tall plants have
long necks and legs; wet areas w/ short plants have
shorter necks
b. Galápagos finches that live in areas w/ hard-shelled nuts
have strong beaks; those that eat fruit have more
delicate beaks.
• An adaptation is a feature that allows 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.
• Darwin found fossils of extinct animals that resemble
modern animals (Glyptodon & Armadillo)
• Darwin found fossil shells high up in the Andes mountains.
Darwin observed fossil and geologic evidence
supporting an ancient Earth.
Fossil Evidence included:
• He saw that land
moved from
underwater to above
sea level due to an
earthquake.
• Darwin extended his
observations to the
evolution of
organisms.
Geologic Evidence Included:
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 a process where humans select traits
through breeding.
neck feathers
crop
tail feathers
• Natural selection is a process in which heritable traits
make it more likely for an organism to survive and
successfully reproduce.
• 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.
• There are four main principles to the theory of natural
selection.
– Variation: heritable differences that exist in every
population
Natural selection explains how evolution can occur.
• There are four main principles to the theory of natural
selection.
– variation
Natural selection explains how evolution can occur.
– overproduction: having many offspring increases the
chance of survival; results in competition for resources.
• There are four main principles to the theory of natural
selection.
– variation
Natural selection explains how evolution can occur.
– overproduction
– adaptation: a certain variation that allows an individual
to survive better than
other individuals it
competes with.
• There are four main principles to the theory of natural
selection.
– variation
Natural selection explains how evolution can occur.
– overproduction
– adaptation
– descent with modification:
Heritability of adaptations;
as long as the conditions
remain beneficial for the
trait, more individuals will
have the trait in every
following generation.
• Fitness is the
measure of
survival ability and
ability to produce
more offspring.
• 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
Evidence for evolution in Darwin’s time came from
several sources.
Fossils
• They are preserved remains of organisms that once lived
• They show evidence for evolution because older layers
are more primitive/simpler than those in the upper layers.
• The study of geography provides evidence of evolution.
Geography
– island species most closely resemble nearest mainland
species
– populations can show variation from one island to
another
• Embryology provides evidence of evolution.
Larva
Adult barnacle Adult crab
– identical larvae, different adult body forms
– similar embryos, diverse organisms
• The study of anatomy provides evidence of evolution.
Human hand Bat wing Mole foot
– Homologous structures are similar in structure but
different in function.
– Are also evidence of a common ancestor.
• 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.
Human hand
Bat wing
Mole foot
Fly wing
• The study of anatomy provides evidence of
evolution.
Analogous structures are not evidence of a recent common
ancestor, but they show that the environment plays a role in
putting pressure on organisms to adapt to the same conditions.