Lamarckism is one of the earliest theories of evolution, proposed before Darwin. It explains how organisms change over time and adapt to their environment.

Sub-topic:-Lamarckism
Topic:-Evolution
By
Laxman Khatal
BO11732:Cell Biology & Evolution
M.Sc

Why?
 Why we study Evolution?

 We study evolution for the same reasons that we study any subject —
the thirst for knowledge, to understand the past and predict the
future, and to organize our world.
 But the subject of evolution also has huge relevance to our
world and current issues that concern all of us.
 Evolution is not just about fossils. It is also about molecules, genes,
mutations, populations, and sex in living organisms. All of these
things are primary sources of data about evolutionary processes that
occur when organisms try to survive and reproduce.
Evolution also is about rigorous analyses — what we must do with the
data to say something that is scientifically defendable.

WHAT IS EVOLUTION?
“Evolution is a process of gradual change that takes place
over many generations, during which species of animals,
plants, or insects slowly change some of their physical
characteristics.”

 MAIN THEORIES OF EVOLUTION :
 Lamarckism or Theory of Inheritance of Acquired character
 Darwinism or Theory of Natural Selection.
 Mutation theory of De Vries.
 Neo-Darwinism or Modern concept or Synthetic theory of evolution.

INTRODUCTION
Lamarck
 First theory of evolution was proposed by
Jean Baptist de Lamarck(1744-1829) .
 French biologist who is best known for his idea that ‘acquired
characters are inheritable, an idea known as Lamarckism, which
is controverted by modern genetics and evolutionary theory.
 He explained it in his famous book Philosophiezoologique
("Zoological Philosophy, or Exposition with Regard to the Natural
History of Animals")
Fig. Lamarck’s Book

Lamarck’s Theory:
Lamarck’s theory includes four main postulates:
1. New needs:
2. Use and disuse of organs:
3. Inheritance of acquired characters:
4. Speciation:Formation of new species

1. New needs:
 Every living organism is found in some kind of
environment.
 The changes in the environmental factors like
light, temperature, medium, food, air etc. or
migration of animal lead to the origin of new
needs in the living organisms, especially
animals.
 To fulfill these new needs, the living organisms
have to exert special efforts like the changes in
habits or behaviour.
Fig. Migrate animals due to
environmental condition.

2. Use and disuse of organs:
 The new habits involve the greater use of certain organs to meet new
needs, and the disuse or lesser use of certain other organs which are of
no use in new conditions.
 This use and disuse of organs greatly affect the form, structure and
functioning of the organs.
Example:

 Continuous and extra use of organs make them more efficient while the
continued disuse of some other organs lead to their degeneration and
ultimate disappearance. So, Lamarckism is also called “Theory of use and
disuse of organs.”
 So the organism acquires certain new characters due to direct or indirect
environmental effects during its own life span and are called Acquired or
adaptive characters.
Vestigial organs in human body Modification of foot in Aquatic birds Wing size reduce in kiwi birds
(Flightless)

3. Inheritance of acquired characters:
 Lamarck believed that acquired
characters are inheritable and are
transmitted to the offspring so that these
are born fit to face the changed
environmental conditions and the
chances of their survival are increased.
 It is also commonly referred to as the
theory of adaptation .
Fig. Inheritance of acquired
characters in offspring.

4. Speciation:Formation of new species:
 Lamarck believed that in every generation,
new characters are acquired and
transmitted to next generation, so that new
characters accumulate generation after
generation.
 After a number of generations, a new
species is formed.
Fig. Formation of new species.

 Evidences in favour of Lamarckism:
1. Phylogenetic studies(evolutionary history and relationships) of horse,
elephant and other animals show that all these increase in their evolution
from simple to complex forms.
Fig. Evolution from simple to complex

2. Giraffe:
Development of present day long-necked and long fore-necked giraffe
from deer-like ancestor by the gradual elongation of neck and forelimbs
in response to deficiency of food on the barren ground in dry deserts of
Africa. These body parts were elongated so as to eat the leaves on the
tree branches. This is an example of effect of extra use and elongation
of certain organs.

3. Snakes:
Development of present day limbless
snakes with long slender body from the
limbed ancestors due to continued disuse
of limbs and stretching of their body to
suit their creeping mode of locomotion
and fossorial mode of living out of fear of
larger and more powerful mammals. It is
an example of disuse and degeneration
of certain organs.
Others evidences:
Aquatic birds feet, Flightless birds reduce wings size,
Horse increase in length of legs and decrease in
functional digits for fast running over hard ground etc.

Due to the evidence against the theory, Lamarck's theories were
subjected to criticism. Some of them are as follows:
Lamarck stated that all the acquired characters are of use to the
organism. Hence, they are inherited to their next generations. But
this was not accepted as all the acquired characters need not be
inherited to the next generation.
Example: The boring of the pinna of the ear which is not carried to
their next generations.
The use and disuse theory has also been criticized due to several
observations. Continuous usage of the eyes or heart did not result in
an increase in size.
 Criticism of Lamarckism:

 Weismann's germplasm theory criticized
Lamarckism that the characters
corresponding to somatic cells cannot be
inherited, and only the characters which
correspond to the germ cells can be
inherited.
 He provided experimental proof for this
theory in which Weismann cut off the tails
of rats for 22 generations and allowed them
to breed. But their offsprings were again
tailed because the cells responsible for the
growth of the tail are somatic and are not
germ cells.
Fig. Weismann’s mice tail experiment

 Significance:
 It was first comprehensive theory of biological
evolution.
 It stressed on adaptation to the environment as a
primary product of evolution.
 Neo-Lamarckism:
 Long forgotten Lamarckism has been revived as Neo-Lamarckism,
in the light of recent findings in the field of genetics which
confirm that environment does affect the form, structure; colour,
size etc. and these characters are inheritable.
 Germ cells may be formed from the somatic cells indicating
similar nature of chromosomes and gene make up in two cell
lines.

Lamarckism Neo-Lamarckism
 It is the original theory given by Lamarck.
 It is a modification of the original theory of
Lamarck in order to make it more suitable to
modern knowledge.
 The theory lays stress on internal vital force,
appetency and use/disuse of organs.
 Neo-Lamarckism does not give any
importance to these factors.
 It believes that change in environment brings
about a conscious reaction in animals.
 The theory stresses on the direct effect of
changed environment on the organisms.
 According to Lamarckism the acquired
characters are passed onto the next
generation.
 Only those modifications are transferred to
the next generation which influence germ
cells or where somatic cells give rise to germ
cells.
Difference between Lamarckism and Neo-Lamarckism:

 The comparison, makes it clear that the point of agreement
between the two theories is the importance of the effect of the
environment on the organism to bring about evolution. however,
even in this they differ in the mechanism.
Neo-Lamarckist accepted that only those changes that
occurred in the germplasm were inherited whereas Lamarckism
made no distinction between somatoplasm and germplasm in
this regard.
 CONCLUSION:

Lamarckism is one of the earliest theories of evolution, proposed before Darwin. It explains how organisms change over time and adapt to their environment.

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Lamarckism is one of the earliest theories of evolution, proposed before Darwin. It explains how organisms change over time and adapt to their environment.