2. Evolution
by
Maryam Riasat
HISTORY AND USEFULNESS OF
EVOLUTION

4. Evolution
 Evolution means descent with modification, or
change in the form, physiology and behavior of
organisms over many generations of time
 Evolution refers to the processes that have
transformed life on earth from its earliest forms to the
vast diversity that we observe today
 Evolutionary change is based mainly on the
interactions between populations of organisms and
their environments

5. History of evolution
 Whenever we say or hear the word evolution, name of Darwin
comes in our mind immediately
 In fact, he was the first person who argued from evidence that
species were not specially created in their present forms rather
they had evolved from ancestral species
 He also proposed a mechanism for evolution which he termed
Natural Selection
 But before Darwin there were theories of biological and
geologic change
 Early scientists proposed ideas about evolution that evolution
is the biological change over time

6. Theories of biological & geologic change
There were three theories of biological & geologic
change:
 Catastrophism: natural disasters such as floods and
volcanic eruptions have shaped landforms and caused
species to become extinct
 Gradualism: changes in landforms resulted from
slow changes over a long period of time
 Uniformitarianism: the geologic processes that
shape Earth are uniform through time

7. Darwin’s theory
 Charles Darwin known as the father of evolution
 He traveled around the world and observed geological phenomena and
adaptations in species
 Published findings in his book Origin of Species in 1800’s
 Followings were his observations during his travel:
o Galapagos tortoises that live in areas with tall plants have long necks and
long legs
o Galapagos tortoises that live in areas with low plants have short necks
and short legs
o Galapagos finches that live in areas with hard-shelled nuts have strong
beaks
o Galapagos finches that live in areas with insects/fruit have long, thin
beaks

9.  Darwin’s theory of evolution by natural selection
explains evolutionary change and adaptation
 He came up with idea of how organisms change over
time (natural selection)
Natural Selection:
A mechanism for change in populations
 It happens when organisms with the best variations
survive, reproduce, and pass their variations on to the
next generation (population increases)
 Organisms that don’t have these variations are less
likely to survive and reproduce (population decreases)

10. Adaptation
 Adaptations develop over many generations
 Living things possess adaptations: i.e., they are well
adjusted in form, physiology, and behavior, for life in
their natural environment
1. Structural Adaptations:
o Mimicry – when one species resembles another species
o Camouflage – enables species to blend in with their
surroundings

12. 2. Variation in Traits
Some beetles are green and some are brown
o Green beetles tend to get eaten by birds and survive to
reproduce less often than brown beetles do
o The surviving brown beetles have brown baby beetles
because this trait has a genetic basis
o The more advantageous trait, brown coloration, which
allows the beetle to have more offspring, becomes more
common in the population
o If this process continues eventually all individuals in
the population will be brown

13. Darwin observed differences among island
species and proved his concept of evolution with
following evidences:
o Biogeography
o Fossil record
o Homologous organ
o Vestigial organ
o Comparative embryology
o Molecular biology

14. Biogeography
 Island species most closely resemble nearest
mainland species
 Populations can show variation from one
island to another
 For example: rabbit fur vs. climate

15. Fossil Record
 How species changed their form/shape over time
 The succession of fossil forms is a strong evidence in
favor of evolution
 It provides a visual record in a complete series
showing the evolution of an organism
 For example the chronological appearance of the
different classes of vertebrate animals in the fossil
record
 Fossil fishes, the earliest vertebrates with amphibians
next followed by reptiles then mammals and birds

16. Homologous Structures
 Structures that have different mature forms in
different organisms but develop from the same
embryonic tissue
 For example arms, wings and flippers are all
constructed from the same basic bones

17. Vestigial structures
 Organs or structures that had a function in an
early ancestor but have lost their function over
time
 The structures reduced in size and often unused
For example:
o Human appendix & tailbone
o Wings on flightless birds (ostrich, penguins)
o Hindlimbs on whales snakes

18. Comparative embryology
 Compare how embryos of different species look during certain
stages of development
 Identical larvae, diverse adult body forms
 Gill slits and “tails” as embryos

19. Molecular biology
 Similarities in DNA, proteins, genes, & gene
products
 Two closely related organisms will have
similar DNA sequences and proteins

20. Other Scientists that influenced Darwin
 Darwin’s contemporaries mainly accepted his idea of evolution
but not his explanation of it by natural selection
 Darwin lacked a theory of heredity. When Mendel’s ideas were
rediscovered at the turn of the twentieth century, they were
initially thought to count against the theory of natural selection
 Fisher, Haldane, and Wright demonstrated that Mendelian
heredity and natural selection are compatible; the synthesis of
the two ideas is called Neo-Darwinism or the synthetic theory
of evolution
 During the 1930s and 1940s, Neo-Darwinism gradually spread
through all areas of biology and became widely accepted
 It unified genetics, systematics, paleontology and classic
comparative morphology and embryology

21. Neo-Darwinism
• It develop in late 1940’s after Mendel work
• An important turning point for evolutionary
theory was the birth of population genetics which
emphasize the extensive genetic variation within
population and recognizes the importance of
quantitative characters
• It is called a synthesis because it integrated
discoveries and ideas from many different fields
including paleontology, taxonomy, biogeography
and population genetics

22.  The use of genetics and the knowledge of
DNA has allowed for analysis of the
similarities and differences between organisms
 Common DNA sequences may support the
theory that they share a common ancestor
 Evolution based on genetic changes - A
generation-to-generation change in the
frequencies of alleles within a population

23.  Hutton & Lyell studied geological change to
show that the Earth changes over time
 Lamarck was the first scientist to recognize
that living things change over time
 Malthus reasoned that if the human population
continued to grow unchecked, sooner or later
there would be insufficient living space and
food for everyone (war, famine and disease
help keep this growth in check)

24. Lamarck’s ideas
 Most-used body structures develop, but unused
ones waste away
 Once a structure is modified by use or disuse,
the modification is inherited by the organism’s
offspring (inheritance of acquired
characteristics)

25. Usefulness of Evolution
 Evolution explains how species are evolved and how the
different species are related
 Evolution suggest a gradual development which is both
ordered and sequential
 Evolution helps an individual in coping up with
environment. Thus it allows better adaptation of organisms
to the changing environment which ultimately leads to the
survival of species. Thus, evolution is necessary for living
organisms
 Evolutionary theory can help us solve real world problems
that have a biological basis, whether that’s figuring out how
to develop antibiotics more effectively or developing a new
pest resistant crop variety

26.  To control hereditary diseases in people, researchers study the
evolutionary histories of the disease causing genes. In this
way, a knowledge of evolution can improve the quality of life
 Humans can speed up natural selection through selective
breeding which can increase food production
 Leads to survival of fittest
 More used body parts developed more efficiently
 Some evolutionary technologies such as population genetics,
production of vaccines and phylogenetic analysis have been
widely applied
 Other areas such as infectious disease and aging research
illustrate the dramatic recent progress made possible by
evolutionary insight