EVOLUTIONARY THEORY
Evolution is the process in which significant
changes in the inheritable traits (genetic
makeup) of a species occur over time.
The validity and value of evolutionary
biology are based on continual analysis
and interpretation of accumulating science
data.
THEORIES OF ORGANIC EVOLUTION
• Historically three theories
• The views of most modern biologists
combine the second and third
• No evidence of the first theory, that of
Lamarck
LAMARCK: Inherited Acquired Characteristics
• Structural variations are due to
functional needs – “to use or
disuse”
• Use of a structure increases its
size.
• Failure to use it decreases its
size
• These variations (now referred
to as “acquired characteristics”
are inherited.
• There is no supporting
evidence in modern biology to
support Lamarck’s idea
LAMARCK: Inherited Acquired Characteristics
A) Theory of need = production of new organ or
appendage results from a need
B) The Theory of Use or Disuse = organs remain
active as long as they are used, but disappear
gradually with disuse
C) Theory of Inherited Acquired Characteristics =
all that has been acquired by the individual is
also inherited by his progeny in the next
generation
LAMARCK: Inherited Acquired Characteristics
LAMARCK: Inherited Acquired Characteristics
CHARLES DARWIN & The Theory
of Natural Selection
CHARLES DARWIN: The Theory of Natural Selection
• His theory was effectively
presented to the world in
1859 when his book “The
Origin of Species” was
published.
• Based on many years of
observations made all over
the world
• Darwin’s Theory rests on 5
principles:
THE ORIGIN OF SPECIES
The Rare Book Collection features a first-edition copy of
On the Origin of Species (1859) with a letter signed by
Charles Darwin on the inside cover
The Theory of Natural Selection
1. All species exhibit
structural and
functional variation.
These affect the
chances of survival
The Theory of Natural Selection
2. By the geometric ratio of
increase (overpopulation)
the numbers of every
species tend to become
enormously large.
Yet the population of each
species remains
approximately constant
because many individuals
are eliminated by
enemies, disease,
competition, climate. etc.
H.M.S. Beagle
The Theory of Natural Selection
3. This involves a “Struggle
for Survival”. Individuals
having variations unsuited to
the particular conditions in
nature are eliminated,
whereas those whose
variations are favourable will
continue to exits and
reproduce
Darwin’s Finches
The Theory of Natural Selection
5. A process of “Natural
Selection” is constant
for better adapted
individuals and the
elimination of less
well adapted ones,
results in
“Evolutionary
Change”
The Theory of Natural Selection
5. The qualities that
promote survival are
passed on from
generation to
generation, thus,
resulting in “The
Survival of The
Fittest” , or
“Preservation of The
Favoured Races”
The Theory of Natural Selection
The Theory of Evolution states that the present
species have descended, with modifications,
from species that existed in the past.
Species are not fixed, unchanging things, but are
constantly evolving.
Evolution is therefore the constant change that
has occurred in our world since its beginning to
the present time
HUGO DeVRIES: Theory of Mutation (1901)
• Dutch Botanist
studied who studied
the plant, Evening
Primrose.
• Observed that out of
50 000 individuals,
800 showed
variations which were
not inherited, and that
mutation occurred
HUGO DeVRIES: Theory of Mutation (1901)
• Evolution has taken
place through the
accumulation of
fortuitous variations
• Due to the appearance
of a series of changes
in the germ-plasm
• These may be
pronounced or minor,
but they are not
equivalent to individual
variations
HUGO DeVRIES: Theory of Mutation (1901)
evening primrose plants