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Evolution- Beliefs about
the origin of life
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Beliefs about the origin of life
 Abiogenesis:
life might arise spontaneously
from nonliving material .
 Panspermia: life might arise from the
molecules from outer space
 Autotroph hypothesis: The first living
organism is an autotroph.
 Heterotroph hypothesis:life might arise from
a chemical evolution.
Heterotroph hypothesis:

The classic experiment demonstrating
the mechanisms by which inorganic
elements could combine to form the
precursors of organic chemicals was
the 1953 experiment by Stanley Miller.
He undertook experiments designed to
find out how lightning--reproduced by
repeated electric discharges--might
have affected the primitive earth
atmosphere. He discharged an electric
spark into a mixture thought to
resemble the primordial composition of
the atmosphere. In a water receptacle,
designed to model an ancient ocean,
amino acids appeared. Amino acids
are widely regarded as the building
blocks of life.
Evidences for Evolution
1.
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Comparative Anatomy
Vestigial Structures
Comparative Embryology
Molecular Biology
Fossil record
Taxonomy
Artificial selection
Biogeography
1. Comparative Anatomy

Scientists often try to determine the relatedness
of two organisms by comparing external and
internal structures.
 Anatomical features in different species that
point to a common ancestor are called
homologous structures. For example, the
flipper of a whale and a human arm seem to be
quite different when looked at on the outside.
But the bone structure of each is surprisingly
similar, suggesting that whales and humans
have a common ancestor way back in prehistory
 These
sorts of structures, which have
superficial similarities because of similarity
of function but do not result from a
common ancestor, are called analogous
structures. bats and insects share a
common ancestor, since both have wings.
But a closer look at the structure of the
wings shows that there is very little in
common between them besides their
function .
2. Vestigial Structures
 In
addition to homologous and analogous
structures, vestigial structures, which
serve no apparent modern function, can
help determine how an organism may
have evolved over time. In humans the
appendix is useless, but in cows and other
mammalian herbivores a similar structure
is used to digest cellulose
3. Comparative Embryology
 In
general, the more
closely related two
species are, the more
their embryological
processes of
development resemble
each other
4. Molecular Evolution
 Two
species that are closely related will
have fewer genetic or protein differences
between them .
Certain genes
or proteins in
organisms
change at a
constant rate
over time.
5. Fossil record
 Fossils
are the traces of past life. They
include footprints, burrows, worm casts.
 Most of the fossils are found embedded in
or on rocks. Paleontology is the science of
studying fossils.
 Relative age of the fossils can be
determined by the geologists by examining
the layers of the earth crust.
 And by the carbon dating methods in which
radioactive isotope of C is examined.
 The
time scale derived from fossil records
is usually calculated from radioactive
dating. For example in carbon-14 dating,
the fact that the ratio of C14 to C12 is fairly
constant (~ 10-12) in living organisms and
that C14 is radioactive with a halflife of
about 5730 years, would yield the age of
the organism since its death (no more
accumulation of C14) if we measure the
leftover amount of C14 in the sample
6. Taxonomy
 The
science of classification is
taxonomy.
 Classification is the process of
grouping the organisms according to
their properties.

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Organisms are classified into larger groups. Species is the smallest
one , kingdom is the largest one.
Kingdom
Phylum
Class
Order
Family
Genus
Species
7. Artificial selection

Artificial selection is to select the animal to
reproduce. It is not randomly
reproduction(natural selection).
 As a result of artificial reproduction some of the
species are selected to reproduce and their
numbers are increased.
 Horse, cereal grains important for agriculture,
chicken
8. Biogeography
 Biogeography
is the study of geographic
distribution of life forms on earth.
Biogeography has an influence on the
adaptation of species to a certain area. In
that way same species adapt to different
areas in different ways and this causes
variation. (adaptation)


Accepted Rules for Evolution
Allen rule
The organisms living in cold areas
have smaller extensions.( small
ear, short tail)
But organisms living in warmer
areas have larger extensions for
heat control.(large ear, long tail)
Bergmann rule


The organisms living in cold areas
have smaller surface area/volume
ratio.( big animals have small surface
area but large volume)
But organisms living in warmer areas
have larger surface area/volume ratio.(
small animals have large surface area
but small volume)
Dollo rule


Evolution always preceeds onwards not backwords.
Life begins in water and proceeds in land. Not goes
back.
Cope rule

Vertebrates tend to increase their
body size during evolution. (to store
important molecules)
Gloger rule

The mammals and birds tend to be
darker near the equatorial region.
(protection against sun rays)
Theories of Evolution
1. Lamarck: Use and Disuse 1809

The classic example used to explain Lamarckism is
the elongated neck of the giraffe. According to
Lamarck’s theory, a given giraffe could, over a
lifetime of straining to reach high branches, develop
an elongated neck. This vividly illustrates Lamarck’s
belief that use could amplify or enhance a trait.
Similarly, he believed that disuse would cause a trait
to become reduced
 The second part of Lamarck’s mechanism for
evolution involved the inheritance of acquired
traits. He believed that if an organism’s traits
changed over the course of its lifetime, the organism
would pass these traits along to its offspring.
2. Darwin: Natural Selection

Each species produces more offspring than can
survive.
 The individual organisms that make up a larger
population are born with certain variations.
 The overabundance of offspring creates a
competition for survival among individual
organisms. The individuals that have the most
favorable variations will survive and reproduce,
while those with less favorable variations are less
likely to survive and reproduce.
 Variations are passed down from parent to
offspring.
Beagle’s trip 1831-1836
 The
competition that Darwin’s theory
describes is sometimes called the
survival of the fittest.
 Most particularly, he took interest in the
islands’ various finches, whose beaks
were all highly adapted to their particular
lifestyles .
The Genetic Basis for Evolution
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Variations exist in the individuals within a
population.
Those variations are passed down from
one generation to the next. (inherited)
If variations favour the survival of the
organism then the organism who carries
these variations will repoduce and fit to
the environment. This is called
adaptation.
Development of New Species Speciation

The scientific definition of a species is a group
of organisms that reproduce within the group
and produces fertile new organisms.
 As populations change, new species evolve.
This process is known as speciation.
 Speciation is also called divergent evolution,
since when a new species develops, it diverges
from a previous form. All homologous traits are
produced by divergent evolution.
 Speciation
occurs when two populations
become reproductively isolated .
Allopatric
speciation occurs
when populations
of a species
become
geographically
isolated so that
they cannot
interbreed .
Sympatric
speciation is the
result of a genetic
isolation without a
geographical
barrier
Over time, the populations may become
genetically different in response to the unique
selection pressures operating in their different
environments. Eventually the genetic
differences between the two populations will
become so extreme that the two populations
would be unable to interbreed even if the
geographic barrier disappeared.