The document summarizes Darwin's theory of natural selection. It explains the key factors of Darwinism: rapid multiplication of organisms, limited environmental resources causing competition, variation between individuals, and survival and inheritance of beneficial traits. Through this process of natural selection over generations, species gradually change and new species may form as variations accumulate. The theory helped explain the evolution of species and adaptation to the environment. It contrasts with Lamarckism in its view of inheritance and lack of internal forces driving evolution.

1. DARWIN’S THEORY OF NATURAL SELECTIONDARWIN’S THEORY OF NATURAL SELECTION
Presented By
Swati Kumari
Roll no: 22
M.Sc. Bioinformatics
3rd
semester
11th July, 2015
CENTER FOR BIOLOGICAL SCIENCES
(BIOINFORMATICS)
CENTRAL UNIVERSITY OF SOUTH BIHAR, PATNA
1

2. ContentsContents

Introduction

Factor of Darwinism
 Rapid multiplication
 Limited environmental resources
 Struggle for existence
 Variation
 Survival of the fittest
 Inheritance of the useful variation
 Formation of new species

Darwinism V/S Lamarckism

References
11th July, 2015 2

3. IntroductionIntroduction

Darwinism : Darwin's Theory of Natural Selection.

The theory of the evolution of species by natural selection
advanced by Charles Darwin announced on July 1, 1858.

Darwin travelled round the world in the 19th century on the ship
H.M.S. Beagle with a surveying expedition for 5 years (1831-1836).

“On the origin of species by Means of Natural Selection “,
November,1859.
311th July, 2015

4. Natural SelectionNatural Selection

Darwin’s most famous and most important theory of evolution.

Only process that promotes adaptation.

The machenism for adaptation and evolution is called “natural
selection”

This theory states that
“ Those organisms best adapted to their environment
have a better chance of surviving and reproducing.”
411th July, 2015

5. Factor of DarwinismFactor of Darwinism
• Rapid multiplication
• Limited environmental resources
• Struggle for existence
• Variation
• Survival of the fittest
• Inheritance of the useful variation
• Formation of new species
511th July, 2015

6. 1. Rapid multiplication (over production)1. Rapid multiplication (over production)
Organism reproduce more offspring than can survive. There is high death rate.
e.g. -
 Paramecium divide 3 times in 48 hours with this rate, a single paramecium will
produce in 5 year a mass of paramecium equal to ten thousand times the size of
earth.
 Plant produce thousands of seed each year.
 cod fish may produce over a million egg in a year. If all the egg developed into fishes,
the whole Atlantic Ocean will be full of cods in Five years.
611th July, 2015
Source: http://www.mosaictraining.ca/fishing/images/stories/whatson%2013.jpg

7. 2. Limited environmental resources (space & food)2. Limited environmental resources (space & food)
• Increase of population in animal & plants requires more space
and food but the universe remains constant.
• Individuals compete for limited resources
• food,
• water,
• spaces,
• mates.
11th July, 2015
7

8. 3. Struggle for existence (competition)3. Struggle for existence (competition)
Competition among members of a species for food, living space,
and other necessities of life.
The Struggle for existence is 3 fold for every individual :-
• Intraspecific struggle
 Within species
• Interspecific struggle
 Different species
• Environmental struggle
 Change in environmental factor
(heat, cold, drought, flood, famine etc..)
811th July, 2015
Source1 : http://www1.umn.edu/ships/evolutionofmorality/images/bears.jpg
Source2 : http://2.bp.blogspot.com/HInvu1MbTf8/U_YQz7wziHI/AAAAAAAAAOk/myTjOyY2LY0/s1600/lion.jpg
Source3 : http://practicalaction.org/images/drought-41562-200.jpg

9. 4. Variation & Adaptation4. Variation & Adaptation
• Understanding how individuals of the same species vary was key to Darwin
developing his theory.
• Because the environment changes, the more variation within a species, the
more likely it will survive.
• Each individual has a unique combination of inherited traits.
• An inherited traits that increase an organism's change of survival is called
“Adaptation”.
Fig : the original species of the finch had a small beak
where it only was able to eat insects and nectar. As
centuries pasted the finch's beak started to curve
downward making the advantage for the bird to tears
bark from trees. However, current finches are nectar
feeders who look closely to a iiwi and that their beaks
are long and curved downward suggest that Darwin's
theory of natural selection made the finches
advantage being able to get nectar from bark and and
flowers.
911th July, 2015
Source : http://evolutionkj.wikispaces.com/file/view/ESCI329NATSEL002.gif/122865717/ESCI329NATSEL002.gif

10. 5. Survival of fittest (natural selection)5. Survival of fittest (natural selection)
• The individuals with the best traits / adaptations will survive
and have the opportunity to pass on it’s traits to offspring.
• Natural selection acts on the phenotype (physical appearance),
not the genotype (genetic makeup).
Fig : some Giraffes have long neck and other
have short neck. Something caused low-lying
shrub to die out, the giraffes with short neck
would not get enough food. After a few
generation all the giraffes would have long
necks.
11th July, 2015 10
source:
http://c3e308.medialib.glogster.com/sandrart/media/4e/4e66c4b4067b382ccca8ba8ed
65d39ace9c79f28/tekamul-07.jpg

11. 6. Inheritance of the useful variation6. Inheritance of the useful variation
• The individual, selected by nature, pass on their useful variation to
the next generation.
• Thus, offspring of fit individual also be fit.
11th July, 2015 11
6. Inheritance of the useful variation6. Inheritance of the useful variation
Source http://image.slidesharecdn.com/evolution-naturalselection2011-111120023730-phpapp01/95/evolution-natural-selection2011-17-728.jpg?cb=1321757091

12. 7.7. Formation of new speciesFormation of new species
• In each generation, new favorable variations appear and
supplement the favorable.
• After a number of generation the variations become so many which
generate a new specie
11th July, 2015 12
Fig : the Origin of Species
source : http://www.kullabs.com/uploads/253.jpg

13. Darwinism v/s LamarckismDarwinism v/s Lamarckism
1. It doesn’t believe in the internal
vital force.
2. These vital force do not form part
of Darwin’s natural selection.
3. An organ can develop further or
degeneration only due to
continuous variation
4. Struggle for existence is vary
important.
5. Only useful variation are
transferred to next generation.
6. Darwin’s natural selection theory
is based on survival of the fittest.
1. There is an internal vital force in
all organism.
2. It consider new need or desire or
produce new structure & change
habits of the organism.
3. According to this theory if organ is
contently used it would be better
developed where as disuse of
organ results in its degeneration.
4. No concept of struggle for
existence
5. All the acquired characters are
inherited to the next generation .
6. Lamarckism does not believe in
survival of the fittest.
11th July, 2015 13

14. ReferencesReferences

http://darwin200.christs.cam.ac.uk/pages/index.php?page_id=d3

Biology, Textbook class XII (NCERT)

Pradeep's A Text Book Of Biology class 12th ; G. Chopra, H.N. Srivastava,
P.S. Dhami.

http://www.apsnet.org/edcenter/advanced/topics/PopGenetics/Pages/Natural
Selection.aspx

http://bivalves.teacherfriendlyguide.org/index.php?
option=com_content&view=article&id=36&Itemid=123

http://nectunt.bifi.es/to-learn-more-overview/mechanisms-of-evolutionary-
change/

http://www.slideshare.net/paprescott/evolution-natural-selection2011-
10239059
11th July, 2015 14

15. 11th July, 2015 15