Download Giant Tortoises of the Galápagos Islands

Chapter 15
Darwin’s Theory
of Evolution
15-1 The Puzzle of Life’s
Diversity
The variety of organisms is called biological
diversity. How did all these different
organisms arise? How are they related?
- Evolution = change over time
- Theory of evolution = a collection of
scientific facts, observations and
hypotheses
Voyage of the Beagle
- Charles Darwin – made numerous
observations and collected evidence that
led him to propose a revolutionary
hypothesis about the way life changes
over time.
- 1831 – He sailed on the HMS Beagle
around the world
- Observed & collected plant and animal
specimens
Darwin’s Voyage
Darwin’s Observations
- He saw variety in traits, method of
reproducing, where they live
- He saw fossils and compared to current
living organisms in area
- Galápagos Islands – 1000 km west of S.
America
- islands had different climates and slightly
different organisms
The Journey Home
Pinta
Pinta Island
Tower
Marchena
Intermediate shell
Fernandina
James
Giant Tortoises of
the Galápagos
Islands
Santa Cruz
Isabela
Santa Fe
Hood Island
Floreana
Hood
Saddle-backed shell
Isabela Island
Dome-shaped shell
Darwin observed that the characteristics of
many animals and plants varied noticeably
among the different Galápagos islands
Galapagos organisms
Galapagos tortoise
Marine Iguana
Frigate bird
Albatross
15-2 Ideas That Shaped Darwin’s
Thinking
An Ancient, Changing Earth
• Hutton and Lyell (geologists) helped
scientists recognize that Earth is many
millions of years old, and the processes
that changed Earth in the past are the
same processes that operate in the
present.
15-2 Ideas That Shaped Darwin’s
Thinking
Lamarck’s Evolution Hypothesis
- Jean-Baptiste Lamarck ( French
naturalist) proposed that by selective
use or disuse of organs, organisms
acquired or lost certain traits during
their lifetime. These traits could then
be passed on to their offspring. Over
time, this process led to change in a
species.
- Organisms have tendency towards
perfection.
- Organisms can alter traits.
- New traits can be passed to offspring.
- Ex: If you lift weights to build muscle,
your children will be born with big muscles.
- This theory has been disproved by many
experiments and observations.
Figure 15–7 Lamarck’s Theory of
Evolution
1. Male uses small claw to attracts mates and wards off predators.
2. Front claw becomes larger through use.
3. The acquired characteristic, a large claw, is passed to offspring.
Population Growth
• Thomas Malthus (economist) reasoned
that if the human population continued to
grow unchecked, sooner or later there
would be insufficient living space and food
for everyone.
15-3 Darwin Presents His Case
- Darwin discovered that the Galápagos
Islands were home to species that are found
nowhere else, but similar to organisms from
S. America.
Publication of On the Origin of Species
- Darwin proposed a mechanism for evolution
called natural selection in the book On the
Origin of Species 1859
Evolution by Natural Selection
- Struggle for existence = Darwin observed
high birth rates and a shortage of basic
needs cause competition
- Fitness = the ability of an individual to
survival and reproduce in its environment
- Adaptation = an inherited characteristic that
increases an organism’s chance of
survival
1. structural = porcupine’s sharp quills
2. physiological = the way a plant does
photosynthesis
3. behavioral = how animals live and hunt
in groups
- Process of survival of the fittest:
1. Individuals in a population compete for
resources
2. Those with characteristics best suited to
the environment survive and reproduce…
pass on the beneficial characteristics
3. Over many generations, the beneficial
characteristics appear in more members
- Ex: Peppered moths of Manchester
- Common descent – principle that all
species, living and extinct, were derived
from common ancestors
Evidence of Evolution
- Fossil record – fossils from deeper rock
layers are older than fossils from shallower
layers
- Geographic distribution of living species –
Darwin saw many different species of
finches in Galápagos Islands… descended
with modification from a common mainland
ancestor
Figure 15–14 Geographic
Distribution of Living Species
Beaver
Beaver
NORTH
AMERICA
Muskrat
Muskrat
Beaver and
Muskrat
Coypu
Capybara
Capybara
SOUTH
AMERICA
Coypu
Coypu and
Capybara
- Homologous Body Structures – structures
that have different mature forms but
develop from the same embryonic tissues
- Ex: limbs of reptiles, birds and mammals
are constructed from same basic bones
- Scientists can compare how similar the
bones are to find degree of relations
Figure 15–15 Homologous Body
Structures
Turtle
Alligator
Ancient lobe-finned fish
Bird
Mammal
- Vestigial organs = organs that are
reduced in size and resemble homologous
organs of other species
- Ex: legs of skinks (lizards), appendix and
tailbone of humans, snakes and whales
have femur and pelvis bones
Vestigial
Organs
- Embryology – The early stages, or
embryos, of many animals with backbones
are very similar
Concept Map
Evidence of
Evolution
includes
The fossil record
Geographic
distribution of
living species
Homologous
body structures
Similarities
in early
development
which is composed of
which indicates
which implies
which implies
Physical
remains of
organisms
Common
ancestral
species
Similar genes
Similar genes
Summary of Darwin’s Theory
- Individuals differ… variation is heritable
- More offspring are born than can survive
- Organisms compete for limited resources
- Organisms best suited for the environment
live, reproduce, and pass on traits…
natural selection
- Species have descended with modification
from common ancestors
Strengths and Weaknesses of
Evolutionary Theory
- Questions as to precisely how new species
arise
- Uncertainty in how life began