Hypothesis and Theory
 A hypothesis is a possible explanation for a set of
observations or a possible answer to a scientific
question.
 A theory is a well-tested explanation that is based on
observations, experimentation, and reasoning. It has
been tested and confirmed as a general principle
helping to explain and predict natural phenomena.
Hypothesis and Theory
 There are several
theories of evolution
today.
 Was Darwin the first
person to develop a
theory of evolution?
 What theory did Darwin
develop that is still
widely-accepted in the
scientific community
today?
Darwin and the Voyage of the
Beagle
 In his early 20’s, Darwin set
sail on the H.M.S. Beagle.
The voyage to the
Galapagos Island was one
of the most important
voyages in science.
 Darwin made numerous
observations and collected
evidence that led him to
propose a revolutionary
hypothesis about the way
life changes over time.
Darwin and the Voyage of the
Beagle
 Over many years of study
and experimentation
supported by a huge
body of evidence, his
hypothesis became a
theory.
 His theory of evolution is
known as the theory of
natural selection.
Darwin and the Voyage of the
Beagle
Darwin and the Voyage of the
Beagle
Galapagos Islands
 He noted that although
the islands were all close
together, they had very
different climates.
 The lowest islands were
hot, dry, and almost
barren. They had sparse
vegetation.
 The higher islands had
greater rainfall and, thus,
rich vegetation. They
had a greater diversity of
plants and animals.
 Darwin observed that
similar species had traits
adapted to the different
environments.
Galapagos Islands
Hood Island
Hood Island
Galapagos Islands
Isabella Island tortoise
Hood Island tortoise
Galapagos Islands
Galapagos Tortoises
 Shape of shell
corresponds to different
habitats.
 Hood tortoise shell is
curved and open around
neck and legs, and a
longer neck. Why?
 Isabela tortoise shell has
a “domed” shell and
shorter neck. Why?
Galapagos Islands
Galapagos Finches
 Darwin wondered about the
changes in shape of bird
beaks from island to island.
So-called cactus finches have
longer, more pointed beaks
than their relatives the
ground finches. Beaks of
warbler finches are thinner
and more pointed than both.
These adaptations make
them more fit to survive on
available food where they
live.
Scientists Who Influenced Darwin
Hutton
 Geologist
 Proposed that layers of
rock form slowly; some are
forced up, some buried,
others pushed up from sea
floor. These rocks, valleys,
and mountains are shaped
by natural forces (rain,
wind, heat/cold). These
processes occur extremely
slowly.
Lyell
 Geologist
 Explained how geological
features could be built up
or torn down over
extremely long periods of
time.
 Ex. Forces raising the
bottom of a sea floor to the
top of a mountain.
Scientists Who Influenced Darwin
Both Hutton and Lyell
 They both provided
evidence for a very old
Earth. At the time,
people thought the
Earth was thousands
of years old. Hutton
and Lyell argued it
must be at least
millions of years old.
 How old do scientists
estimate the Earth to be
today?
Darwin asked himself, if
the Earth changes over
time, couldn’t life change,
too? That would only be
possible if the Earth were
extremely old.
Scientists Who Influenced Darwin
Scientists Who Influenced Darwin
Scientists Who Influenced Darwin
LaMarck
Recognized before Darwin that living things changed
(evolved) over time.
According to Lamarck, organisms altered their behavior in
response to environmental change. Their changed
behavior, in turn, modified their organs, and their offspring
inherited those "improved" structures.
3 main hypotheses (Q- Why aren’t they theories?)
 Tendency toward perfection
 Use and Disuse
 Inheritance of Acquired Characteristics
Scientists Who Influenced Darwin
Tendency Toward
Perfection
 LaMarck believed all
organisms had a natural
tendency toward
perfection. They
“strived” to become
better-adapted to their
environment through
their behavior.
Scientists Who Influenced Darwin
Use and Disuse
 LaMarck believed
organisms can alter the
size/shape of organs (or
make a new one appear)
by using them in new
ways. Conversely, an
organ could decrease in
size or go away if it was
not used.
Scientists Who Influenced Darwin
LaMarck believed that
organisms “needed” to
become more perfect,
and out of this will and
their behavior,
developed new
adaptations.
Scientists Who Influenced Darwin
Inheritance of Acquired
Characteristics
 LaMarck believed
acquired characteristics
were passed to offspring.
 Ex: giraffes that
stretched their necks
would have babies with
long necks
What did LaMarck have no
knowledge of which could
explain why he believed
this? DNA!
Did Darwin have
knowledge of DNA?
NO
Scientists Who Influenced Darwin
Thomas Malthus
 Noticed babies were
being born faster than
people were dying
 Reasoned that if the
human population
continued to grow
unchecked, there would
not be enough food and
living space
 Forces he thought
controlled growth were
war, famine, and disease.
 When Darwin read
Malthus’s work, he
reasoned it applied even
more strongly to plants
and animals b/c they
produce far more
offspring than humans.
Scientists Who Influenced Darwin
 This is him, the real
Thomas Malthis!
 He is a real “looker”!
Carolus Linnaeus
 Developed a system for
classification of
organisms.