EVOLUTIONARY THEORY

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