Transcript Evolution - Zanichelli online per la scuola

David Sadava, David M. Hillis,
H. Craig Heller, May R. Berenbaum
La nuova
biologia.blu
Le cellule e i viventi
Evolution of Life
What Is the Relationship between Fact and Theory in Evolution?
Evolution is the change in genetic composition
of populations over time.
These genetic changes drive the origin and
extinction of species and the diversification of
life.
Evolutionary theory is the understanding of
the mechanisms of evolutionary change.
What Is the Relationship between Fact and Theory in Evolution?
The young Charles Darwin was passionately
interested in geology and natural history.
In 1831 he was recommended for a position on
the HMS Beagle, for a five-year survey voyage
around the world.
What Is the Relationship between Fact and Theory in Evolution?
In the Galápagos Islands he observed that species
were similar to, but not the same as, species on the
mainland of South America. He also realized that
species varied from island to island.
What Is the Relationship between Fact and Theory in Evolution?
These observations, and many others, led Darwin to
propose an explanatory theory for evolutionary change
based on three propositions:
• Species change over time.
• Divergent species share a common ancestor, and
species have diverged gradually through time
(descent with modification).
• The mechanism that produces the change is natural
selection.
Darwin published his book, The Origin of Species, in
1859.
Artificial Selection
Artificial selection is the purposeful selection
of specific phenotypes by humans.
How Do Scientists Date Ancient Events?
Earth’s history is recorded in rocks. Layers of
rocks are called strata.
Relative ages of rocks can be determined by
looking at strata of undisturbed sedimentary rock.
The oldest layers are at the bottom, youngest at
the top.
How Do Scientists Date Ancient Events?
Earth formed 4.6 to 4.5 billion years ago but it was 600
million years or more before life evolved.
The history
of Earth can
be pictured
as a 30-day
month.
How Do Scientists Date Ancient Events?
The history of life is divided into four eons.
Precambrian (4 billion years)
Phanerozoic eon—diversification of eukaryotes
What Are the Major Events in Life’s History?
By the late Precambrian (630–542 mya) and early
Cambrian, many kinds of multicellular soft-bodied
animals had evolved.
What Are the Major Events in Life’s History?
Cambrian period: beginning of the Paleozoic
era.
A rapid
diversification
of life took
place called the
Cambrian
explosion.
What Are the Major Events in Life’s History?
Ordovician period
A great radiation of marine organisms occurred.
Silurian period
The first vascular plants appeared, as well as
some terrestrial arthropods—scorpions and
millipedes.
What Are the Major Events in Life’s History?
Devonian period
Rates of evolutionary change accelerated in many
groups.
An extinction at the
end of the
Devonian resulted
in loss of 75% of
marine species.
Two meteorite
impacts may have
contributed to this
extinction.
What Are the Major Events in Life’s History?
Carboniferous period
Great swamp forests of horsetails and tree ferns grew
on the tropical continents.
These swamp plants became fossilized as coal.
Diversity of terrestrial animals increased and insects
evolved wings.
What Are the Major Events in Life’s History?
Permian period
The continents came together to form the
supercontinent Pangaea.
Differentiation of
two lineages:
reptiles and
mammals.
Near the end of the
Permian about
96% of all species
became extinct.
What Are the Major Events in Life’s History?
At the start of the Mesozoic era, the surviving
organisms inhabited a relatively empty world.
Triassic period
Pangaea began to
break apart. On land,
conifers and seed
plants became
dominant.
A great radiation of
reptiles began.
A mass extinction at
the end eliminated
about 65% of species.
What Are the Major Events in Life’s History?
Jurassic period
Pangaea divided into Laurasia, which drifted
northward, and Gondwana, which drifted
southward.
First lizards and flying reptiles (pterosaurs)
appeared; most large terrestrial animals were
dinosaurs.
Several groups of mammals first appeared.
Flowering plants appeared late in this period.
What Are the Major Events in Life’s History?
Cretaceous period
Dinosaurs continued to diversify and snakes appeared.
Flowering plants began
the radiation.
By the end of the
period, many mammal
groups had evolved.
Another mass
extinction at the end of
the Cretaceous was
caused by a meteorite.
What Are the Major Events in Life’s History?
Cenozoic era
The positions of the continents resembled those of
today.
Tertiary period
Grasslands spread.
Birds and Mammals began
the radiation.
Quaternary period
Many large mammal species
became extinct in Australia and
the Americas when Homo
sapiens arrived—possibly due
to hunting pressure.
Adapted from
Life: The Science of Biology, Tenth Edition, Sinauer Associates, Sunderland, MA, 2014
Inc. All rights reserved