Introduction to Evolution

Chapter One
05/12/21
By: Asmamaw menelih Department of Biology
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Learning outcomes
At the end of this chapter the students should able to:
 Define Evolution
 Describe briefly the difference between Evolution and Biological Evolution
 Explain briefly the scope and importance of Evolution
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Definition of Evolution
What is Evolution?
The term evolution means change over time and most of the people agree with statement.
However, this statement is a correct definition when discussing about non biological evolutions such the
evolution of computers and the evolution of solar system.
 What is Biological Evolution?
This can be defined as the change in heritable characteristics of biological populations over successive
generations or reproduction periods.
The biological definition of evolution is also defined as an inherited change within a linage.
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To understand the biological definition of evolution, let see the following terms.
Inherited.
 All organisms reproduce and pass their genes to their offspring.
 Each new generation inherits their genes and associated traits from their parents.
Change.
 The new generation is not an exact replica of the parental generation.
 Sexually reproducing organisms get half of their genome from each parent, so the result in each offspring is a
combination.
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Lineage.
 As each generation reproduces it creates continuous chain of genetic inheritance from
ancestors to descendants.
All together, these three concepts detail the biological definition of evolution.
Evolution has been defined as a gradual and orderly change from one condition to another.
The principle of evolution implies the development of an entity in the course of time through a
gradual sequence of changes, from a simple to a more complex state.
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The science that deals about evolution of organisms is called Evolutionary Biology.
It is the subfield of biology that studies the evolutionary processes (natural selection, common
descent speciation) that produced the diversity of life on Earth.
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Scope of Evolution
 Scope: refers to the boundary or area in which deals with or includes in a particular field of
study.
 Evolution is the unifying theory that explains all the biological sciences.
 All life is connected and of it can not be fully understand without the theory of evolution.
 Evolutionary scientists from different fields of biology such molecular biology, genetics,
botanical sciences, zoological sciences etc. are doing sophisticated research to explain life.
Generally Evolution has a wide range scopes with different disciplines from both natural
and social sciences.
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Evolution
Genetics
Paleontology
Anthropology
molecular
biology
History
Geology
Botany
Zoology
Geography
computer
science
statistics
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Scope of Evolution

Importance of Evolution
Knowing the evolutionary relationships among species allows scientists to choose appropriate
organisms for the study of diseases, such as HIV.
Scientists are even using the principles of natural selection to identify new drugs for detecting and
treating diseases such as cancer
Understanding evolution is critical for understanding biology.
As the preeminent scientist Theodosius Dobzhansky stated, “Nothing in biology makes
sense except in the light of evolution.”
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 Evolution is the only scientific explanation for the diversity of life.
 It explains the striking similarities among vastly different forms of life, the changes that occur within
populations, and the development of new life forms.
 The principles of evolution underlie improvements in crops, livestock, and farming methods.
 Natural selection accounts for the rise in pesticide resistance among agricultural pests.
 Evolution is important design of new technologies to protect crops from insects and disease.
 Excluding evolution from the science curricula or compromising its treatment deprives students of this
fundamental and unifying scientific concept to explain the natural world.
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Importance of Evolution

Chapter two
2. Historical Development of Evolution
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Learning outcomes:
At the end of this chapter the students should able to:
Describe the historical development of Evolution
Describe the contributions of different Scientist for the development of Evolution
Differentiate Non evolutionary and evolutionary thoughts
Explain the difference between Darwinism and Neo- Darwinism
Define and explain different theories that contribute a for the development of modern
Evolution
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Introduction
The medieval period is characterized as Dark Age.
During this period, misconception and blind following of ancient thinkers succeeded and
Aristotelian reasoning and the spirit of scientific inquiry were died out.
Thus, no progress occurred in the idea of evolution during medieval period.
With the Renaissance, interest in the natural sciences accelerated and increasing
knowledge about different kinds of animals.
These led more and more scientists to consider the concept of evolution favorably.
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Evolutionary and Non-evolutionary ideas before Darwin
 Darwin was not the first naturalist to propose that species changed over time into new species.
 In the eighteenth century, Buffon and other naturalists began to introduce the idea that life might not have
been fixed since creation.
 By the end of the 1700s, paleontologists had swelled the fossil collections of Europe, offering a picture of
the past at odds with an unchanging natural world.
 And in 1801, a French naturalist named Jean Baptiste Pierre Antoine de Monet, Chevalier de Lamarck
took a great conceptual step and proposed a full-blown theory of evolution.
 Thus, before Charles Darwin, several possible mechanisms have been proposed to account for the
evolution.
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Jean Baptiste Lamarck
Jean Baptiste Lamarck (1744-1829) is one of the best-known early evolutionists.
In 1809 he published a book Philosophie Zoologique
He described a two part mechanism by which change was gradually introduced into the
species and passed down through generations.
1. Use and disuse
2. Inheritance of acquired characteristics
His theory is alternatively referred to as the theory of transformation or simply
Lamarckism.
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George Cuvier
Lamarck’s most passionate opponent was a French vertebrate paleontologist named
Georges Cuvier (1769–1832).
Cuvier introduced the concept of extinction to explain the disappearance of animals
represented by fossils.
Cuvier proposed a variation of a doctrine known as catastrophism.
Catastrophism was the belief that the earth’s geological features are the results of
sudden, worldwide disastrous events.
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Cuvier’s version of catastrophism suggested that a series of regional disasters had
destroyed most or all of the local plant and animal life in many places.
These areas were then restocked with new, similar forms that migrated in from
unaffected regions.
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George Cuvier

Charles Lyell
Charles Lyell (1797–1875) is considered the founder of modern geology.
Published a book Principles of Geology
In his book Lyell argued that the geological processes we see today are the same as those
that existed in the past.
This theory, called geological uniformitarianism
 Lyell demonstrated forces such as wind, water erosion, local flooding, frost, decomposition of vegetable
matter, volcanoes, earthquakes, and glacial movements had all contributed in the past to produce the
geological landscape that we see today.
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 According to processes were ongoing, indicating that geological change was still
happening and that the forces driving such change were consistent, or uniform, over
time.
 Various aspects of the earth’s surface (mountain ranges, rivers, the position of continents,
and so forth) vary through time, but the underlying processes that influence them are
constant.
 Lyell also emphasized the slowly acting forces to produce momentous change.
 This shows that the earth must be far older than anyone had previously suspected.
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Charles Lyell

Darwin’s Theory (1859)
 Charles Darwin (1809–1882) was one of six children of Dr. Robert and
Susanna Darwin.
 As a boy, Darwin had a keen interest in nature, but this interest did little to dispel the
generally held view among family and friends that he was in no way remarkable.
 His father sent him to Edinburgh University to study medicine.
 It was there that Darwin first became aware with the evolutionary theories of Lamarck
and others.
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 Darwin invited to join a scientific
expedition that would circle the globe.
 The famous voyage of the Beagle would
take almost five years and would
forever change not only the course of
Darwin’s life but also the history of
biological science.
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Darwin’s Theory (1859)

What did Darwin during the Beagle’s Voyage?
 He was collected different specimens of Organisms and fossils.
 He was also critically observed the nature in each moment.
 Darwin was also puzzled by where different species lived and didn’t live.
 For example, he visited Argentina and Australia which had similar grassland ecosystems.
 However, those grasslands were inhabited by very different animal species.
 Also neither Argentina nor Australia was home to the sorts of animals that lived in
European grasslands.
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Con’t
 As a result, for Darwin, these patterns posed challenging questions;
 Why were there no rabbits in Australia, despite the presence of habitats that seemed
perfect for them?
 Similarly, why were there no Kangaroos in England?
 From his Collection, some fossils resembled organisms that were still alive.
 Others looked completely unlike any creature he had ever seen.
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Con’t
 Of all the Beagale’s voyage, the one that mostly influenced Darwin was a group of small
islands located 1000km west of South America.
 These islands are called Galapagos Islands.
 Darwin noted that although they were close together, the islands had very different
climates.
1. The smallest and lowest islands were hot, dry and nearly barren.
2. Hood islands: had spars vegetation
3. The higher islands had greater rainfall and a different assortment of plants and animals.
4. Isabela islands: had rich vegetation.
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Con’t
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Con’t
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Beak variation in Darwin’s Galápagos finches.

Con’t
Darwin began to develop his views on what he called natural
selection.
He conclude that under these circumstances favourable variations
would tend to be preserved, and unfavourable ones to be destroyed.
The result of this would be the formation of a new species”.
Finally Darwin concluded that natural selection is the main driver
for the formation of new species (evolution).
He also published his scientific journal Origin of Species in 1858.
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Other Naturalists
1. Alfred Russel Wallace (1823-1913)
 was a naturalist who independently proposed the theory of evolution by natural
selection.
 He was a man of many talents - an explorer, collector, naturalist, geographer,
anthropologist and political commentator.
 Most famously, he had the revolutionary idea of evolution by natural selection entirely
independently of Charles Darwin
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2. Ernst Haeckel (1834-1919)
 He was a German zoologist, naturalist, philosopher, physician, professor, marine biologist, and artist
who discovered, described and named thousands of new species, mapped a genealogical tree relating all
life forms.
 Ernst Haeckel proposed the theory of Biogenetic Law in 1866.
 The biogenetic law is a theory of development and evolution.
 He is also known by his the famous statement "ontogeny recapitulates phylogeny",
 Ontogeny recapitulates phylogeny" mean that the development of an organism (ontogeny) expresses all
the intermediate forms of its ancestors throughout evolution (phylogeny).
 Haeckel also discovered many microbes, and coined several scientific terms commonly known today,
such as ecology, phylum, and stem cell.
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August Weismann
 He was a German biologist and one of the founders of the science of Genetics.
 Weismann postulated the theory of germplasm in 1892 to explain heredity.
 According to this theory the bodies of organisms contain two types of cells namely
somatic cells and germplasm cells.
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De Veries and William Bateson
 De Veries was a Dutch botanist and geneticist who introduced the
experimental study of organic evolution.
 He was best known by his mutation theory.
 William Batson was a British biologist who founded and named the science of
genetics and his experiments provided evidence basic to the modern
understanding of heredity.
 He coined the term genetics from the word gene in 1905.
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Karl Pearson (1857-1936)
 Karl Pearson's Coefficient of Correlation is widely used mathematical method
wherein the numerical expression is used to calculate the degree and direction of the
relationship between linear related variables.
 The coefficient of correlation is denoted by “r”.
 The Pearson correlation coefficient, often referred to as the Pearson R test, is a
statistical formula that measures the strength between variables and relationships.
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The Modern synthesis of
Evolution
 Darwin’s theory of natural selection was accepted
 The strong supporters of Darwinism are
 Wallace
 Ernst Haekel
 August Wesimann
 How ever, Darwins theory lacked an input of modern concepts of genetics and
the mechanisms , how characters appear and persist in a population
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By: Asmamaw Menelih
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Cont.…
 In the light of recent researches the theory was modified.
 Several experimental evidences have gone in favor of Darwinism.
 Based on those facts and statistical data a synthetic theory of evolution has been proposed.
 This modified theory of Darwinism also called Neo-Darwinism.
 The synthetic theory emerged by the synthesis of the original idea given by Charles Darwin and addition
of new Knowledge of :
 Genetics
 Population dynamics
 statistics
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By: Asmamaw Menelih
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Cont.…
 Neo- Darwinism is the most modern theory of Evolution and has been constantly improved during
20th century by the contributions of many scientists from different fields.
 Eg, - R. A. Fisher
 J.B.S haldane
 Ernst maller
 G.G Simpson
 T. Dobzhansky
 H.J. Muller
 H. De veries
 G.L. Stebbins
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By: Asmamaw Menelih
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Contributed their studies
on population dynamics
Added information on the basis of genetics
and mutation

Cont.…
 Hardy, W. Weinberg and Sewall wright also did extensive work on population
genetics & statistics which help to understand the mechanisms of heredity.
 According to Neo- Darwinism the following factors operate for the formation of new
species.
 Variations
 Mutations
 Natural selections
 Genetic drift
 Isolation of species.
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By: Asmamaw Menelih
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Introduction to Evolution

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