Transcript Ideas That Shaped Darwin`s Thinking

Darwin and Evolution
16-1 Darwin’s Voyage
16-2 Ideas that shaped his thinking
16-3 Darwin presents his case
16-4 Evidence of Evolution
Darwin’s Inspiration
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James Hutton
Charles Lyell
Jean-Baptiste Lamarck
Thomas Malthus
James Hutton-1785
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Proposed that:
layers of rocks form very slowly or are moved up
from the Earth’s surface
Earth had to be millions of years old and not a
few thousand years old
Earth is shaped by geological forces that took
place over extremely long periods of time
Charles Lyell-1833
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Explained that awesome geological features could be
built up or torn down over long periods of time
Helped Darwin appreciate the significance of
geological phenomena
Jean-Baptiste Lamarck-1809
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Proposed that by selective use or disuse of organs,
organisms lost or acquired certain traits
Proposed that all organisms had a built in tendency
toward complexity and perfection
Proposed that organisms could alter the size or shape of
particular organs by using their bodies in new ways
Lamarck cont.
Thought
that acquired characteristics could be
inherited
If you spent much of your life lifting weights
to build muscles, your children would inherit
big muscles
*Didn’t know how traits were inherited*
•Was one of the first to develop a scientific
hypothesis of evolution and realize that
organisms are adapted to their environments
Thomas Malthus-1798
Studied population growth
•Said that if the human pop. Continued to grow
unchecked, sooner or later there would be
insufficient living space and food for everyone
•Supported by observation made on the
streets of London
Darwin’s Case
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Charles Darwin (1809–
1882)of South
coast
concluded that animals on the
America that resembled those on the nearby
islands evolved differences or descended with
modification after separating from a common
ancestor
25 years later he published On the Origin of
Species after hearing that Alfred Wallace was
coming to the same evolutionary conclusions
Proposed a mechanism for evolution that he called
natural selection
Inherited Variation &
Artificial Selection
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Inherited variation-caused by the variations in genes
Artificial selection-nature provides the variation and
humans select those variations that are found useful
Produced many diverse domestic animals and crop plants
Natural Selection
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Struggle for existence-members of each species
compete regularly to obtain food, living space, and other
necessities for life
Fitness-ability of an individual to survive an reproduce in
its specific environment
Adaptation-any inherited characteristic that increases
an organism’s chance of survival
Natural Selection cont.
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Survival of the Fittest-ability to survive and reproduce
most successfully
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Individuals that are best suited to their
environment, with adaptations that enable
fitness, survive and reproduce most
successfully
Individuals with characteristics that are not
well suited to their environment, with low levels
of fitness, either die or leave few offspring
Natural Selection cont.
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Darwin referred to survival of the fittest as NATURAL
SELECTION
In both artificial and natural selection only certain
individuals of a population produce new individuals
In natural selection, traits being selected contribute to
an organisms fitness (over time)
NS cannot be seen directly; it can only be observed as
changes in a pop. over many successive generations
Descent with Modification
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Darwin proposed that each living species has descended,
with changes, from other species over time (descent
with modification)
Common Descent- all species, living or extinct, were
derived from common ancestors
Evidence of Evolution
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Darwin argued that living things have been
evolving on Earth for millions of years
Evidence could be found in the fossil record,
geographical distribution of living species,
homologous structures of living organisms, and
similarities in early development
Fossil Record
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Formation of Fossils -evidence of orderly change
can be seen when fossils are arranged according
to their age.
Darwin saw fossils as a record of history of life
on Earth
Showed that life had been evolving for millions of
years
Homologous Structures
Homologous structures describes similar body
structures that come from common ancestry
 HS are structures that have different mature forms
but develop from the same embryonic tissues
*not all homologous structures serve important
functions*
 Vestigial organs-homologous structures that are so
reduced in size that they serve no function
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Vestigial Organs
Homologous Structures
Forelimbs
Homologous
structures
Birds
Alligators
Bats
Hind limbs
Evolution
Humans
Whales
Vestigial
structures
Human hemoglobin
Gorilla
Rhesus monkey
Molecules
Mouse
Lamprey
Frog
Chicken
Similarities in Embryology
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In early stages of development, chickens, turtles,
and rats look similar, providing evidence that they
shared a common ancestry.
•ex. see right picture - The embryos
of the tortoise, chick, rabbit, and
human resemble one another due to
the distinguishing tail, gill slits, and
overall shape during early
development.
Evolutionary Theory
Strengths:
– Scientific advances in biology and physics have
confirmed and expanded most of Darwin’s
hypotheses
Weaknesses:
– Researches still debate about how new
species arise and why they become extinct
*There is still uncertainty about how life began*