This document discusses several key concepts and theories related to evolution: 1. It describes Lamarck's theory of evolution which proposed that acquired traits could be inherited. It notes this theory is no longer supported. 2. It summarizes Darwin's theory of evolution by natural selection, noting the key principles of overproduction, variation, adaptation, and natural selection. 3. It discusses Hugo de Vries' mutation theory which proposed evolution occurs through accumulation of mutations in genes. 4. It notes the modern synthesis combines Darwinian evolution through natural selection with Mendelian genetics.

1. NIRBHAY SUDHIR PIMPLE
Theories of evolution

2. • Prior to the studies of Charles Darwin, the
most widespread belief was that all known
species were created at the same time and
remainedunchanged throughout history.
Somescientists at the time believed that
featuresan individual acquired during a
lifetime could bepassed onto its offspring, and
the species could gradually change to fit an
environmentbetter.
Evolution
•
A scientific theory is NOT just a belief, it is a well-supported tested
explanation.
2.1

3. Evolution
Descent with Modification
Evolution means change over time
Evolution can also be defined more narrowly as a change in the genetic
composition of a population from generation to generation.

4. Fossils
• A fossil is the
preserved remains
or imprints of
ancient organisms.
Someone who
studies fossils is
called a
paleontologist.
•
• Fossils are
found in
sedimentary
rock formed
when sand and
silt settle to the
bottom of
water.

5. Typesof radioactive dating
• Potassium-Argon dating is
used for rocks that are
suspected billions of years
old.
In older rocks the ratio of
Argon to 4
0
Kwill be higher
than in youngerrocks.
•
•
•
Carbon dating: 2types
1
4
C:1
2
C
– Radioactive 1
4
C
– Non-radioactive 1
2
C,most
common

6. feathers
thin
ribs
teeth
long tail
claws
wing-like
forelimbs
Reptile-like features
Bird-like features
Replica of Archaeopteryx fossil;
half bird half reptile
Evidences for Evolution Fossil Record

7. Vertebrate Limbs
The basic pattern of the vertebrate limb is represented by the
human arm skeleton shown below
ball and
socket joint
hinge joint
single bone two
bones
group of
small
bones
five jointed
digits
Evidence from comparative Anatomy

8. The forelimbs of the following vertebrates show the
basic pattern of limb bones with modifications which
are adapted to their methods of locomotion.
Lizard Bird
Dolphin Bat
The basic pattern suggests they have evolved
from a common ancestor
19

9. DNA evidence
Another important line of evidence for evolution comes
from DNA analysis
Organisms which have much of their DNA in common must
be closely related, i.e. they have split from a common
ancestor comparatively recently (in geological terms)
For example, humans and chimpanzees have 99% of
their DNA in common which suggests a close
relationship and relatively ‘recent’ divergence from a
common ancestor

10. 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.
In words of Charles Darwin evolution is Descent with
modification

11. Theories of Organic Evolution
Historically three theories
1. Lamarck’s Theory of Evolution,
2. Darwin’s Theory of Evolution,
3. De Vries Mutation Theory of
Evolution.
The views of most modern biologists
combine the second and third
No evidence of the first theory, that of
Lamarck’s Use and disuse theory.

12. Jean Baptiste Lamarck, 1744-1829
• French geologist and naturalist
• published Philosophie
Zoologique in 1809
• Speculated about mechanisms
of biological evolution, offered
no evidence

13. In 1809 Jean-Baptiste Lamarke hypothesized that “simple”
organisms emerge spontaneously and evolve to greater
“complexity”.
Principles to his theory
1. Organisms constantly strive to improve
themselves.
2. Most used body structures develop and
unused waste away. (Use and Disuse)
3. A structure is modified by use or disuse, the
modification is inherited to the offspring.
(Inheritance of acquired characteristics).

14. • Structural variations are dueto
functional needs – “to use or
disuse”
Useof astructure increases its size.
Failure to use it decreasesitssize
Thesevariations (now referred to as
“acquired characteristics” are
inherited.
There is no supporting evidencein
modern biology to support
Lamarck’s idea
•
•
•
•

16. Disproving Lamarck
• Characteristics acquired during the lifetime of a parent are not
passed onto the offspring
• An athlete who develops a large muscle mass through training
does not have children who already possess this large muscle
mass
• Ernst Haeckel
In an attempt to disprove Lamarckism he is said to have cut off
the tails of mice for several generations
• The babies born from this line of tailless mice still grew tails
as long as their ancestors
• This was not exactly a fair test as the mice had not stopped
using their tails in an attempt to adapt to their environment
• They still found their tails useful

17. 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.
• Darwin’s Theory rests on 5
principles:

18. 5 principles of Darwin’s Theory
1. Overproduction
- All species have a tendency and the potential to
increase at a geometric rate.
All organisms produce more organisms but only a few
survive.
2. Competition
- The conditions supporting life are limited.
For eg Food, water and other resources are limiting.
-Only a fraction of the offspring in a population will live
to produce offspring, so that the number of individuals
in a population remains fairly constant.

19. 3. Variation
-Individuals in a population vary greatly in their
characteristics.
4. Adaptation
-Some variations enable individuals to produce more
offspring than other individuals.
5. Natural Selection
-Individuals having favorable traits will produce more
offspring, and those with unfavorable traits will produce fewer
offspring.
• Speciation
- Given time, natural selection leads to the accumulation of
changes that differentiate groups from one another, such that a
new species may arise.

20. 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

21. THE ORIGIN OF SPECIES

22. Variation in a population. Individuals in this
population of Asian ladybird beetles vary in color
and spot pattern. Natural selection may act on
these variations only if (1) they are heritable and
(2) they affect the beetles’ ability to survive and
reproduce.

23. Overproductionof offspring.
Asingle puffball fungus can produce billions of offspring.
If all of these offspring and their descendants survived to maturity,
they would carpet the surrounding landsurface.

24. The Theory of Natural Selection
Darwin’s Finches

25. Industrial Melanism
The Peppered Moth (Biston betularia)
Before Industrial revolution After Industrial revolution

26. Evolution of drug-resistant
pathogens
Evolution of insecticide resistance
pests
Giraffe Necks

27. Hugo De Vries: Theory of Mutation (1901)
• Dutch Botanist studied
who studied the plant,
EveningPrimrose.
Upon observing wild
evening primrose,Hugo
•
different from
found that they were
the
cultivated primrose

28. • He took some of the wild primrose seeds back to his
garden where he made many new variations.
• He bred the plants and followed traits through several
generations, like mendel.
The evening primrose Plant

29. Hugo De Vries: Theory of Mutation (1901)
• Evolution has taken place
through the accumulation of
fortuitous variations or
Mutations
• Due to the appearance of a
series of changes in the germ-
plasm or genes
• These may be
pronounced or minor

30. Neo Lamarckism
This is reinvention of the Lamarck’s theory of Inheritance of
acquired characters. Where constant use tend to strengthen the organ
whereas failure of the use leads to atrophy
Lamarck rejected the notion that the environment would directly
affect organismal traits and neo lamarckism incorporates these
things.
Neo-Darwinism
Neo-Darwinism is incorporated in the modern synthesis theory.
Darwinian evolution through Natural selection with Mendelian
genetics, the latter being a set of primary tenets specifying that
evolution involves the transmission of characteristics from parent to
child through the mechanism of genetic transfer, rather than the
'blending process'

31. Modern Synthesis Theory
Important points of Modern Evolutionary Theory
All evolutionary phenomena can be explained in a way
consistent with known genetic mechanisms.
Evolution is gradual: small genetic changes regulated by natural
selection accumulate over long periods. Discontinuities amongst
species are explained as originating gradually through
geographical separation and extinction.
Natural selection is by far the main mechanism of change.
Thinking in terms of populations rather than individuals, is
primary: the genetic diversity existing in natural populations is a
key factor in evolution