1. Evolution
Popular Belief
• Prior to the studies of Charles Darwin, the most
widespread belief was that all known species were
created at the same time and remained unchanged
throughout history.
• Some scientists at the time believed that features an
individual acquired during a lifetime could be passed
onto its offspring, and the species could gradually
change to fit an environment better.
A scientific theory is NOT just a belief, it is a well-supported tested
explanation.
2.1
2. 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.
3. Fossils
• A fossil is the preserved • Fossils are found in
remains or imprints of sedimentary rock
ancient organisms. formed when sand and
silt settle to the bottom
• Someone who studies of water.
fossils is called a
paleontologist.
4. Types of radioactive dating
• Carbon dating: 2 types
• Potassium-Argon dating is
used for rocks that are • 14C:12C
suspected billions of years – Radioactive 14C
old. – Non-radioactive 12C, most
• In older rocks the ratio of common
Argon to 40K will be higher
than in younger rocks.
5. Evidences for Evolution Fossil Record
claws
wing-like
forelimbs
teeth
thin
ribs
long tail
feathers
Reptile-like features
Replica of Archaeopteryx fossil;
half bird half reptile Bird-like features
6. Evidence from comparative Anatomy
Vertebrate Limbs
The basic pattern of the vertebrate limb is represented by the
human arm skeleton shown below
ball and group of
hinge joint small
socket joint
bones
single bone two
bones five jointed
digits
7. 19
The forelimbs of the following vertebrates show the basic
pattern of limb bones with modifications which are adapted
to their methods of locomotion.
The basic pattern suggests they have evolved from a common
ancestor
Lizard Bird
Dolphin Bat
8. 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
9. 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
10. 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.
11. Jean Baptiste Lamarck, 1744-1829
• French geologist and naturalist
• published Philosophie
Zoologique in 1809
• Speculated about mechanisms
of biological evolution, offered
no evidence
12. 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).
13. • 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
14.
15. 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
•
16. 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:
17. 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.
18. 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.
19. 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. 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.
22. Overproduction of offspring.
A single puffball fungus can produce billions of offspring.
If all of these offspring and their descendants survived to maturity,
they would carpet the surrounding land surface.
26. Hugo De Vries: Theory of Mutation (1901)
• Dutch Botanist studied
who studied the plant,
Evening Primrose.
• Upon observing wild
evening primrose, Hugo
found that they were
different from the
cultivated primrose
27. • 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
28. 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
29. 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'
30. 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
