Darwin`s Evolution

Darwin’s Theory of Change Over Time
•Evolution, or change over time, is the process by which modern
organisms have descended from ancient organisms.
•The theory of evolution can explain Earth’s biodiversity.
•A scientific theory is an explanation of natural events that is
supported by evidence and can be tested with new evidence.
Voyage of the Beagle
•Charles Darwin: The individual who contributed more to our
understanding of evolution than anyone.
•H.M.S. Beagle set sail from England in 1831 for a voyage around
the world.
•During Darwin’s travels, he made numerous observations and
collected evidence that led him to propose a revolutionary
hypothesis about the way life changes over time.
Section 15-1
Darwin’s Voyage
Darwin’s Observations
•Darwin observed many organisms. He saw that many plants and
animals were very well suited to their environment.
•Darwin collected fossils, or the preserves of ancient organisms.
•Some of the fossils were unlike any creatures he had ever seen.
•Darwin wondered why the species in the fossils had disappeared.
Darwin’s Observations
•Darwin’s observation on the Galapagos Islands (group of small islands
west of South America) influenced him the most.
•The islands are near one another but have different climates.
•Darwin saw that the characteristics of many animals and plants varied
noticeably among the different islands.
•He wondered whether animals on different islands had once belonged
to the same species.
•According to this hypothesis, these separate species would have
evolved from an original ancestor species after becoming isolated from
one another.
Galapagos Islands
Giant Tortoises of the Galápagos Islands
Pinta Island
Intermediate shell
Santa Cruz
Santa Fe
Hood Island
Isabela Island
Dome-shaped shell
Saddle-backed shell
Ideas That Shaped Darwin’s Thinking
•In Darwin’s day, most Europeans thought that Earth and all of
its life forms had existed for only a few thousand years.
•They also thought that species did not change.
•Some scientists of Darwin’s time began challenging these ideas.
•These scientists influenced the development of Darwin’s theory
of evolution.
An Ancient, Changing Earth
•James Hutton and Charles Lyell helped scientists recognize that
Earth is many million years old, and that it changed over time.
• These ideas helped Darwin realize that life might change as
•Knowing that Earth was very old convinced Darwin that there
had been enough time for life to evolve.
Movement of Earth’s Crust
rocks form in
horizontal layers.
When part of Earth’s
crust is compressed,
a bend in a rock
forms, tilting the rock
As the surface
erodes due to water,
wind, waves, or
glaciers, the older
rock surface is
New sediment is
then deposited
above the exposed
older rock surface.
Geological Change
Lamarck’s Evolution Hypothesis
•Jean-Baptiste Lamarck was on of the first scientist to see that evolution
•He also recognized that organisms adapt to their environment.
•Lamarck proposed that by selective use or disuse of organs, organisms
acquired or lost certain traits during their life time. These traits could
then be passed on to their offspring.
•Over time, this process led to change in species.
•Scientists now know that some of Lamarck’s ideas were wrong. (can’t
control what traits are passed on to the next generation) However, his
general ideas about evolution and adaptation are correct.
Lamarck’s Theory of Evolution
Population Growth
•Economist Thomas Malthus also influenced Darwin.
•Malthus thought that if the human population kept growing,
sooner or later there would be insufficient living space and food
for everyone.
•Darwin thought this was true for all organisms.
Darwin Presents His Case
•Darwin was hesitant to publish his ideas because they were
so extreme.
•When he learned that scientists Alfred Russell Wallace has
the same ideas, Darwin published On the Origin of Species in
•In the book, Darwin supplied evidence that evolution has
occurred. He also explained his ideas about how evolution
Inherited Variation and Artificial Selection
•Darwin’s theory was based on artificial selection. In artificial
selection, nature provided the variation, and humans selected
those variations that they found useful.
•Example, animal breeders used only the largest hogs, fastest
horses, or cows that produced the most milk for breeding.
Artificial Selection
Evolution by Natural Selection
•Darwin thought that a similar process occurs in nature. He
called this natural selection. This process can be summed up as
– Individuals differ, and some of the differences can be
passed on to their offspring.
– More offspring are produced than can survive and
– There is competition for limited resources, or a struggle for
Natural Selection
Evolution by Natural Selection Continued
– Individuals best suited to their environment survive and
reproduce most successfully. In other words, there is
survival of the fittest.
• Fitness is the ability to survive and reproduce in a
given environment. It results from adaptations.
• Adaptations are inherited traits that increase an
organism’s chance of survival. Only the fittest
organisms pass on their traits. Because of this, a
species changes over time.
Evolution by Natural Selection Continued
•Darwin argued that species alive today descended with
modification from species of the past.
•Darwin also introduced the principle of common descent.
Evidence of Evolution
•Darwin argued that living things have been evolving on Earth
for millions of years.
•He presented four types of evidence in support of evolution.
– The fossil record: Comparing fossils from older and
younger rock layers provides evidence that evolution has
taken place.
– Geographic distribution of living species: The presence of
similar but unrelated organisms in similar environments
suggests the action of natural selection.
Fossil Record
Geographic Distribution of Living Species
Beaver and
Coypu and
Evidence of Evolution Continued
– Homologous structures of living organisms:
Homologous structures have different mature forms
but develop from the same embryonic tissues. They
provide strong evidence that organisms have
descended, with modifications, from common
• Some homologous structures no longer serve major
roles in descendants. If the structures are greatly
reduced in size, they are called vestigial organs. For
example, the appendix in humans is a vestigial
organ. It caries out no function in digestion.
Evidence of Evolution Continued
– Similarities in early development: The early stages, or
embryos, of many animals are very similar. These
similarities are evidence that the animals share common
Concept Map
Evidence of
The fossil record
distribution of
living species
Homologous body
in early
which is composed of
which indicates
which implies
which implies
Physical remains
of organisms
ancestral species
Similar genes
Similar genes
Strengths and Weaknesses of Evolutionary Theory
•Scientific advances have upheld most of Darwin’s hypotheses.
However, evolutionary theory continues to change as new data
are gathered and new ways of thinking arise.
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