This document provides an overview of Darwin's theory of evolution by natural selection. It discusses pre-Darwinian thought on the age of the Earth and origins of life. It then explains Darwin's development of the theory of evolution through gradual processes like variation and natural selection. The theory proposes that all species descend from common ancestors, and diversity arises through the multiplication and branching of species over time.

1. JIMMA UNIVERSITY COLLEGE OF
NATURAL
SCIENCE
EVOLUTION GROUP ASSIGNMENT
DEPARTMENT OF
BIOLOGY

2. Group 2

3. EVOLUTION
• E V O L U T I O N I S A P R O C E S S O F G R A D U A L D E V E L O P M E N T
I N A P A R T I C U L A R S I T U A T I O N O R T H I N G O V E R S O M E
T I M E .
• I N B I O L O G Y E V O L U T I O N I S T H E C H A N G E I N H E R I T A B L E
T R A I T S O F B I O L O G I C A L P O P U L A T I O N S O V E R
S U C C E S S I V E G E N E R A T I O N S . E V O L U T I O N A R Y P R O C E S S E S
G I V E R I S E T O D I V E R S I T Y A T E V E R Y B I O L O G I C A L
O R G A N I Z A T I O N L E V E L . A L L L I F E O N E A R T H S H A R E S A
C O M M O N A N C E S T O R K N O W N A S T H E L A S T U N I V E R S A L
A N C E S T O R .
• E V O L U T I O N I S O N E O F T H E M O S T F U N D A M E N T A L
O R G A N I Z I N G P R I N C I P L E S O F T H E B I O L O G I C A L S C I E N C E S
A N D A S S U C H I S T H E S I N G L E M O S T D O M I N A N T T H E M E I N
B I O L O G Y T O D A Y

4. PRE DARWIN THOUGHT
I N D A R W I N ’ S T I M E S C I E N T I S T S W E R E B E G I N N I N G T O R E A L I Z E
T H A T T H E W O R L D W A S M U C H O L D E R T H A N P R E V I O U S L Y T H O U G H T
A . B E F O R E D A RW I N T H E A C C E P T E D A G E O F
T H E E A R T H WA S D E T E R M I N E D B Y J A M E S
U S S H E R ( 1 5 8 1 - 1 6 5 6 ) & J O H N L I G H T F O O T
( 1 6 0 2 - 1 6 7 5 )
 M A D E A S S U M P T I O N T H A T T H E B I B L E W A S T H E O N L Y R E L I A B L E
S O U R C E O F C H R O N O L O G I C A L I N F O R M A T I O N F O R T H E T I M E
C O V E R E D I N B I B L I C A L W R I T I N G S
 A R R I V E D A T T H E C A L C U L A T I O N T H A T T H E E A R T H W A S C R E A T E D
O N S U N D A Y , O C T O B E R 2 4 , 4 0 0 4 B C
 L I G H T F O O T , M A K I N G A D D I T I O N A L A S S U M P T I O N S P U T T H E T I M E
A T 9 : 0 0 A M
 S O T H E E A R T H W A S B E L I E V E D T O B E ~ 6 0 0 0 Y E A R S O L D

5. PRE DARWIN THOUGHT...
B . I N T H E N E X T C E N T U R Y , C O M T E D E B U F F O N ( 1 7 0 7 - 1 7 8 8 ;
 “ H I S T O I R E N A T U R E L L E ” , 1 7 4 9 ) B E L I E V E D H E C O U L D G E T A N
E S T I M A T E O F T H E A G E O F T H E E A R T H B A S E D O N I T S R A T E O F
H E A T L O S S
 H E C A L C U L A T E D T H E A G E O F T H E E A R T H A S 7 4 , 8 3 2 Y R S ( A N D
T H E O R I G I N O F L I F E A T 4 0 , 0 0 0 Y R S )
 H E A L S O R E C O G N I Z E D 6 G E O L O G I C A L P E R I O D S
 M U C H O F W E S T E R N S C I E N C E A T T H I S T I M E W A S S T I L L
D O M I N A T E D B Y C H U R C H B E L I E F S A N D H E W A S H E A V I L Y
P R E S S U R E D B Y T H E C H U R C H T O R E C O N S I D E R H I S
C A L C U L A T I O N S
 H I S S O L U T I O N : “ T H I S I S W H A T O N E M I G H T T H I N K I F O N E D I D N O T
K N O W W H A T G E N E S I S S A Y S ”

6. PRE DARWIN THOUGHT.....
C. by Darwin’s time geologists were beginning to realize that the earth was 100’s of millions or
even billions of years old
eg. palaeontologists were learning that fossils were representatives of previous forms of life from
the ancient past
much earlier, fossils were thought of as “sports of nature” by 1700’s most scientists believe that
fossils were of organic origin but most were explained in terms of the Biblical flood
as geologists were realizing the extreme age of the earth that that would mean that fossils
trapped in these ancient layers were also millions of years old
eg. previous biologists had already suggested that
 all species are interrelated
 species change through time
 and the environment is a factor in that change
Jean Baptiste de Lamark (1809) produced the first “evolutionary tree” to illustrate “change through
time” but he could not offer a reliable explanation or “mechanism for how these processes could
occur

7. THEORY OF EVOLUTION
 T H E T H E O R Y O F E V O L U T I O N W A S D E V E L O P E D B Y C H A R L E S D A R W I N , I N
T H E M I D 1 8 0 0 ’ S , A F T E R A L I F E T I M E O F T R A V E L , O B S E R V A T I O N ,
E X P E R I M E N T A T I O N A N D D I S C U S S I O N .
 C H A R L E S D A R W I N W A S A B R I T I S H N A T U R A L I S T W H O P R O P O S E D T H E
T H E O R Y O F B I O L O G I C A L E V O L U T I O N B Y N A T U R A L S E L E C T I O N . 1 2
F E B R U A R Y 1 8 0 9 – 1 9 A P R I L 1 8 8 2 )
 D A R W I N D E F I N E D E V O L U T I O N A S " D E S C E N T W I T H M O D I F I C A T I O N , " T H E
I D E A T H A T S P E C I E S C H A N G E O V E R T I M E , G I V E R I S E T O N E W S P E C I E S ,
A N D S H A R E A C O M M O N A N C E S T O R .
 D A R W I N I S C O N S I D E R E D T H E F A T H E R O F E V O L U T I O N . I N T R U T H , D A R W I N
A R R I V E D A T H I S T H E O R Y O F E V O L U T I O N A T T H E S A M E T I M E A N O T H E R
S C I E N T I S T , A L F R E D R U S S E L L W A L L A C E , C A M E T O T H E S A M E
C O N C L U S I O N .
 H O W E V E R , D A R W I N W A S A R E S P E C T E D S C I E N T I S T E V E N B E F O R E H E
W R O T E O N T H E O R I G I N O F S P E C I E S .
Alfred Russell Wallace
Charles Darwin

8. THEORY OF EVOLUTION
 T H E M E C H A N I S M T H AT D A R W I N P R O P O S E D F O R
E V O L U T I O N I S N AT U R A L S E L E C T I O N .
 D A R W I N ' S T H E O R Y C O N S I S T E D O F T W O M A I N
P O I N T S ;
1 . D I V E R S E G R O U P S O F A N I M A L S E V O LV E F R O M
O N E O R A F E W C O M M O N A N C E S T O R S ;
2 . T H E M E C H A N I S M B Y W H I C H T H I S E V O L U T I O N
TA K E S P L A C E I S N AT U R A L S E L E C T I O N .
 D A R W I N ' S T H E O R Y O F E V O L U T I O N , A L S O
C A L L E D D A R W I N I S M
I T C A N B E F U R T H E R D I V I D E D I N T O 5 PA R T S :
1 . E V O L U T I O N A S S U C H ,
2 . C O M M O N D E S C E N T,
3 . G R A D U A L I S M ,
4 . M U LT I P L I C AT I O N O F S P E C I E S , A N D

9. EVOLUTION AS SUCH
1 . E V O L U T I O N A S S U C H .
 T H I S I S T H E T H E O R Y T H AT T H E W O R L D I S N O T
C O N S T A N T N O R R E C E N T LY C R E AT E D N O R
P E R P E T U A L LY C Y C L I N G B U T R AT H E R I S S T E A D I LY
C H A N G I N G A N D T H AT O R G A N I S M S A R E T R A N S F O R M E D
I N T I M E .

10. COMMON DESCENT
2 . C O M M O N D E S C E N T,
 T H I S I S T H E T H E O R Y T H A T E V E R Y G R O U P O F O R G A N I S M S
D E S C E N D E D F R O M A C O M M O N A N C E S T O R , A N D T H A T A L L
G R O U P S O F O R G A N I S M S , I N C L U D I N G A N I M A L S , P L A N T S ,
A N D M I C R O O R G A N I S M S , U L T I M A T E L Y G O B A C K T O A
' S I N G L E O R I G I N O F L I F E O N E A R T H ' .

11. MULTIPLICATION OF SPECIES
3 . M U L T I P L I C AT I O N O F S P E C I E S
T H I S T H E O R Y E X P L A I N S T H E O R I G I N O F T H E E N O R M O U S
O R G A N I C D I V E R S I T Y. I T P O S T U L A T E S T H A T S P E C I E S
M U L T I P L Y, E I T H E R B Y S P L I T T I N G I N T O D A U G H T E R S P E C I E S
O R R Y ' ' B U D D I N G , ' ' T H A T I S B Y T H E E S T A B L I S H M E N T O F ,
G E O G R A P H I C A L L Y I S O L A T E D F O U N D E R P O P U L A T I O N S T H A T
E V O L V E I N T O N E W S P E C I E S

12. GRADUALISM
4 . G R A D U A L I S M
 A C C O R D I N G T O T H I S T H E O R Y, E V O L U T I O N A R Y
C H A N G E T A K E S P L A C E T H R O U G H T H E G R A D U A L
C H A N G E O F P O P U L AT I O N S A N D N O T B Y T H E S U D D E N
( S A LT A I O N A L ) P R O D U C T I O N O F N E W I N D I V I D U A L ' S
T H AT R E P R E S E N T A N E W T Y P E .

13. NATURAL SELECTION
5 . N AT U R A L S E L E C T I O N
 A C C O R D I N G T O T H I S T H E O R Y ; E V O L U T I O N A R Y C H A N G E ,
C O M E S A B O U T T H R O U G H T H E A B U N D A N T P R O D U C T I O N O F
G E N E T I C V A R I A T I O N I N E V E R Y G E N E R A T I O N . T H E R E L A T I V E L Y
F E W I N D I V I D U A L S W H O S U R V I V E , O W I N G T O A P A R T I C U L A R L Y
W E L L - A D A P T E D C O M B I N A T I O N O F I N H E R I T A B L E C H A R A C T E R S ,
G I V E R I S E T O T H E N E X T G E N E R A T I O N .

14. NATURAL SELECTION
 N A T U R A L S E L E C T I O N I S A S I M P L E M E C H A N I S M T H A T C A U S E S
P O P U L A T I O N S O F L I V I N G T H I N G S T O C H A N G E O V E R T I M E .
 I N F A C T , I T I S S O S I M P L E T H A T I T C A N B E B R O K E N D O W N I N T O
F I V E B A S I C S T E P S , A B B R E V I A T E D H E R E A S V I S T A :
 V A R I A T I O N ,
 I N H E R I T A N C E ,
 S E L E C T I O N ,
 T I M E A N D
 A D A P T A T I O N

15. THEORY OF EVOLUTION
The Theory of Evolution by Natural Selection at its core is a relatively
simple idea:
A.Variation
 all living things consist of a unique combination of chemicals
organized in unique ways.
 In all species, individuals differ in their genetic makeup, producing
many variations in their physical features; individuals in a
population vary from each other.
 variations occur in every species which means no two individuals
of a species are alike
B. Inheritance
 most of these variations have a genetic basis
 they can be passed on to their offspring
 Darwin was not aware of Mendel’s work,
 He didn’t know HOW traits were passed on, just observed that
some were took another 50-60 yrs before hereditary information
was added to Darwin’s original theory
NATURAL SELECTION

16. 1
C. Selection
 those individuals whose variations best fit their environment
will be more likely to survive and reproduce
fitness = ability to reproduce
 organisms with less favourable variations will be less likely
to survive
 "There is a “struggle for existence”
 " with “survival of the fittest”
D.TIME
 each species produces more offspring than will survive into
maturity
eg. if not, 1 bacterial cell -> 36 hours would cover earth 3-4 ft
deep
eg. fruit fly -> in 7 months would produce enough offspring to
NATURAL SELECTION

17. NATURAL SELECTION
E. Adaptation
 species’ populations are able to adapt to gradually
changing environments.
 same species in different parts of the world have
different tolerances and slightly different
characteristics to survive the local conditions in
which it lives.
eg. live oak in Austin, vs live oak in Baton Rouge
eg. flower and gardening catalogues vs local
growers
 still they are the same species:
 they interbreed naturally where they come to
contact

18. SUMMARY
 Generally a process of natural selection, evolution sorts through these
numerous variations within a population and “chooses” the most fit
combination
 as the environment slowly changes and certain variations are selected
over 100’s or 1000’s of generations new forms will arise.

19. REFERENCE
https://www.khanacademy.org/science/ap-biology/natural-selection/natural-selection-ap/a/darwin-
evolution-natural-selection.
https://www.sparknotes.com/biology/evolution/darwin/summary/#:~:text=Darwin%27s%20theory%
20of%20evolution%2C%20also,population%20speciation%2C%20and%20natural%20selecti
on.
https://www.amnh.org/exhibitions/darwin/evolution-today/natural-selection-
vista#:~:text=In%20fact%2C%20it%20is%20so,%2C%20Selection%2C%20Time%20and%20
Adaptation.
https://biodiversity.ku.edu/sites/all/themes/bootstrap/bootstrap_biotheme/img/public_html/sites/all/t
hemes/bootstrap/bootstrap_biotheme/img/photos/schools/pdfs/Investigating_VIST_Principles.
pdf
https://biocyclopedia.com/index/general_zoology/darwins_theory_of_evolution.php#:~:text=The%
20theories%20are%20(1)%20perpetual,and%20(5)%20natural%20selection.
https://www.snscourseware.org/snsctnew/files/1679905244.pdf