Biology SME

Key unit competence
Analyze the relevance of theories of evolution and explain the process of
speciation.

Introductory activity 1

During Kwita Izina Ceremony (naming a newborn Gorilla) in Rwanda. On
Rwanda television I saw an image of mountain gorilla, it was closely related
to human being. Later while I was reading biology book I found this image
which shows human being and their ancestors

a) Observe carefully the image above and record the similarities among
A and D, and D and F.
b) Write a short note of your observation about the image.

6.1 Theories of evolution

Activity 6.1

1) Observe the diagram below of plant (vegetables), do you see any
relationship among those types of vegetables

According to the most biologists the principal questions in biology is “where do
all living things come from?” but we know that life comes from the pre-existing
life means that every species descends from other species, it is what we call
“evolution”

Evolution is a changeover successive generation of inheritable trait of a
population or it is the process by which new species are formed from pre-
existing ones over a period of time. As there is emergence of new species
others are disappearing, the species that disappear are said to become extinct.
An enormous fossil, such as those of early birds, provides evidence of evolution.
Genetics studies of populations of bacteria, protists, plants, insects, and even
humans provide further evidence of the history of the change among organisms
that live or have lived on earth.

Theory of evolution is a short term for theory of evolution by natural selection
which was proposed by Charles Darwin and Alfred Russel Wallace in the
nineteenth century.

Four main theories of evolution are known:
• Lamarckism or theory of inheritance of acquired characters
• Darwinism or theory of natural selection.
• Neo-Darwinism or modern concept or Synthetic theory of evolution and
• Creation Theory.

a) Lamarckism
Lamarckism or theory of inheritance of acquired characters developed by Jean
Baptist Lamarck (1744-1829) French Biologist. His theory is based on the
inheritance of acquired characteristic (variations) in the body of organism in the
response to the environment conditions

i) Assumptions of Lamarck’s theory
• Organisms tend to increase in size as they become more complex to a
predetermined limit.
• When influenced by the environment, body changes can be induced in
organisms.
• Organisms acquire new features because of need.
• Development of an organ and its effectiveness is promoted by its use
whereas its disuse brings about decline.
• Acquired features are inherited by future generations.

ii) Merits/Advantages
• Lamarck was able to show that the environment influences the course of
evolution.
• He observed that features are passed down from parents to their offspring.
• He was able to recognize that as organism increase in size, they become
more complex to a predetermined limit. (Predetermine: to determine or
decide in advance)

iii) Demerits /disadvantages
• Acquired changes are not heritable as they are influenced by genes.
• Somatic changes are not heritable as they are not passed through
reproduction.
• The process of gametogenesis is not related to occupation or their activity.
• Use or disuse of somatic cells does not affect gamete formation.

b) Darwinism
The evolution is not a modern concept, since the ancient time, philosophers,
Aristotle, Socrates, Confucius and others have suggested that complex species
evolved from simple pre-existing ones by a process of continuous and gradual
change. In nineteenth century Charles Darwin an A. Wallace published the paper
describing their theory of evolution by natural selection later on 24 November
1859 Darwin published the book “The origin of species by means of Natural
selection or the preservation of favoured races in the struggle for life’’ containing
many evidence to support the theory.

According to Darwin’s theory:
– Each species living today arose from a pre-existing species.
– All species have evolved from one ancestral type.
– Natural selection provides the mechanism for one species to change
into another.

The main evidence for his first suggestion, which has been called descent with
modification, comes from fossils.

Darwin use different observations in his research including the following:
a) Reproductive powers of living organism/over production/biotic
potential: Over production is the production of more offspring that can
be supported by the available resources this ensures the surviving of a
high number of offspring and the geometric or exponential growth of the
population.
b) Scarcity of resources: Darwinism states that, the increase of the
population geometrically is not directly proportional to the increase of
resources (food, space...) which increase in arithmetic way.
c) Struggle for existence: Darwin deduced on the basis of 1 and 2 that
members of the species were constantly competing with each other in an
effort to survive. In this struggle for existence only a few would live long
enough to breed
d) Survival of the fittest by natural selection: Among the offspring there
will be some better able to withstand the prevailing conditions. That is,
some will be better adapted (fitter) to survive in the struggle for existence.
These types are more likely to survive long enough to breed. Darwin’s idea
of evolution by natural selection is relatively simple but misunderstood. To
find out how it works, imagine a population of beetles:

i) Variation in the beetles’ population some are green and some brown

ii) Green beetles tend to reproduce less as they are eaten by predators than
brown one

iii) Surviving beetles pass they brown genes to their offspring

iv) The brown coloration the important trait which allows the beetles to have
more offspring and to survive, will dominate the population and eventually
all beetles will be brown.

e) Inheritance of useful trait/like produce like: The selected individuals
produce offspring with the useful trait so that they can fit into the
environment.

Darwin’s theory was based on three main observations:
i) Within a population are organisms with varying characteristics, and these
variations are inherited (at least in part) by their offspring.
ii) Organisms produce more offspring than are required to replace their
parents
iii) On average, population numbers remain relatively constant and no
population gets bigger indefinitely.

After his observations Darwin concluded that within a population many individuals
do not survive and fail to reproduce.

Assumptions of Darwinism
– Most organisms have the potential to produce large number of
offspring or progeny than the environment can support. This leads to
still competition as the numbers of organisms are fairly stable.
– All organisms, even of the same species vary in a few characteristics,
– Only those organisms of a given species with variations that adapt them
to the environment, survive the competition and live. There is survival for
the fittest by natural selection.
– The features favored/selected by nature survive and are inherited.
Therefore, new species may develop by natural selection, which is one
of the forces of evolution.

 Merits of Darwin’s theory of natural selection
– Species always change as the environment changes.
– Species are compared with their ancestors due to presence of
similarities in characteristics.
– Enough data are / can be collected for explaining variation in a population
that may result into formation of a new species.

 Demerits of Darwin’s theory of natural selection
– Not all variations inherited, except for only genetic variations.
– It provides inadequate explanation of existence of many vestigial
structures in organisms.
– Explanation on deleterious mutations that are retained in a population
is not adequate.

c) Neo-Darwinism
Neo-Darwinism is the modern theory of evolution that incorporates scientific
evidence particularly from genetics and molecular biology, the Neo-Darwinism
combine the work of Mendel genetics and Darwin, for example, we now know that

the variations that are so important in natural selection come about by random
and spontaneous changes in genes, particularly from mutations in reproductive
cells. According to Neo-Darwinism, nature selects those individuals with
beneficial mutations and allows them to be passed to their offspring through
reproduction from generation to generation. The mutations are transmitted
within the population and if selected by nature, they may form a new species.

d) Special creation
It is believed that a special being, God created the universe and all living
organisms (bible Genesis 1:1-2; Psalm 139:13-14). In this theory, heavens and
earth were first created. Light, day and night were created next and subsequently,
all living things with human beings the last in the creation. It shows that there
was direct creation of organism with no precursor to life.

6.1. 1 Evidence for evolution

a) Fossils
The evidence for evolution are provided mainly by the study of fossil
(paleontology). Fossils come into different forms, such as imprints, the burrow
of worm, or mineralized bone preserved by natural process in rocks, ice etc. The
study of fossils show how the organisms have changed over time.

Relative and radiometric dating are the method used by scientist to determine
the age of fossils and rocks.

b) Anatomy and Embryology
Anatomy or comparative anatomic structures is the study of biological different
organisms. Structures in different species that have similar internal frame, work,
position and embryonic development are said to be homologous. For example,
bones in the appendages of a human, dog, bird, and whale all share the same
overall construction resulting from their origin in the appendages of a common
ancestor. Overtime, evolution led to changes in the shapes and sizes of these
bones in different species, but they have maintained the same overall layout.

Paleontologists have found fossils showing how the bones of lizard-like ancestor
evolved into the ear bones of modern mammals.

The fact that two different organisms look alike does not always suggest a
close evolutionary relationship. Structures of unrelated species can evolve
to look alike because structures are adapted of similar functions. These are
called analogous structures. Another evidence is vestigial structures
body structure with no function or which do not serve their original purpose but
probably useful in the ancestors.

c) Comparative embryology
The study for embryo it is called embryology, an embryo is an unborn or
unhatched animal or human young in its earliest phases. Therefore, species that
show a similar embryonic development are assumed to be closely related, even
if the adult stages are very different. For example, echinoderms (the phylum
containing starfish and sea urchins) are believed to be related to chordates (the
phylum including vertebrates) because of similarities in their early embryonic
development.

d) Comparative biochemistry and cell biology
The most persuasive evidence that organisms have evolved from a common
ancestor comes from studies comparing the cell biology and biochemistry of
different organisms, which reveal that:
– The genetic code contained within nucleic acids is almost universal
– Physiological processes vital to all organisms, such as respiration,
   follow very similar metabolic pathways.

– ATP is the universal energy currency
The cellular and biochemical details of organisms are quite similar, but any
differences can give an idea of how closely different species are related.
Species that are closely related would be expected to differ only slightly from
each other. Detailed comparisons of DNA, metabolic pathways, key proteins,
and organelles such as ribosomes have been used to work out the evolutionary
relationships of organisms. For example, ribosomes inside mitochondria and
chloroplast are similar to those in bacteria, suggesting that these organelles
may have evolved from bacteria. Mammalian blood proteins can be tested to see
how similar they are to human blood proteins: blood serum from the mammal in
question is added to rabbit serum containing anti-human antibodies.

Application Activities 6.1

1) The diagram below indicates the part of front limb of different animals,
if the labeled diagram is an arm of human being label other diagram by
corresponding them, according to how they have evolve

2) The skull of chimpanzee and that of human being are shown her below

The above diagram corresponds to the adult skull, relate them with their fetus
3) Correct this statement
Mitochondrial DNA differences are inconsistent with the existence of a recent
human common ancestor for all ethnic groups.

6.2 Cause of evolution

Activity 6.2

Find out the cause of evolution and discuss it among your classmates.

It is difficult to meet Hardy-Weinberg equilibrium in real populations. The
Hardy-Weinberg Theorem describes populations in which allele frequencies
are not changing means that it does not evolve.
The force behind evolution are mainly summarized in four factors:
• Competition changes in the environment.
• Sexual reproduction.
• Mutations.
• Gene recombination.
• Industrialization.
• Effect of drugs or chemical resistance.
• Artificial selection.

a) Competition changes in the environment
Imagine that we are plunged into a new ice age. The climate becomes much
colder, so that snow covers the ground for almost all of the year. Assuming
that rabbits can cope with these conditions, white rabbits now have a selective
advantage during seasons when snow lies on the ground, as they are better
camouflaged (like the hare in figure 6.3.). Rabbits with white fur are more likely
to survive and reproduce, passing on their alleles for white fur to their offspring.
The frequency of the allele for white coat increases at the expense of the allele
for agouti. Over many generations, almost all rabbits will come to have white
coats rather than agouti.

b) Sexual reproduction
Sexual reproduction is a reproduction using gametes (male gametes and female
gametes) each gamete contain a unique set of gene combination, and the ova is
fertilized randomly by the male gamete as a result each zygote is unique hence
the variation among individuals.

c) Mutation
Mutation creates new genetic variation in a gene pool. It is how all new alleles first
arise. In sexually reproducing species, the mutations that matter for evolution are
those that occur in gametes. Only these mutations can be passed to offspring.
For any given gene, the chance of a mutation occurring in a given gamete is
very low. Thus mutations alone do not have much effect on allele frequencies.
However, mutations provide the genetic variation needed for other forces of
evolution to act

d) Gene recombination
Natural selection is usually the most powerful mechanism or process causing
evolution to occur, however, it only selects among the existing variation already
in a population. It does not create new genetic varieties or new combinations or
varieties. One of the sources of those new combinations of genes is recombination
during meiosis. It is responsible for producing genetic combinations not found
in earlier generations.

e) Industrialization
Many species of organisms, especially insect species, have two or more
adult body forms that are genetically distinct from one another, but which are
contained within the same interbreeding population. This condition is known as
polymorphism (another type of natural selection). The peppered moth (Biston
betularia), for example, has two main forms with different wing colours. One form
has pale wings with dark markings; the other form is called melanic because the
wings contain large amounts of melanin (a black pigment), so they are almost
black.

f) Effect of drugs or chemical resistance
Drug resistance is a reduction in effectiveness of medication such as
antimicrobial in treating a disease or condition. Antibiotic resistance is a severe
problem throughout the world. For example, some strains of the common
bacterium Staphylococcus aureus are resistant to antibiotics such as penicillin
and methicillin. Penicillin resistance has probably evolved in the following way:
– By chance, a mutation produces an individual bacterium with an allele
that allows it to produce an enzyme, penicillinase, which deactivates
penicillin.
– This bacterium is immediately resistant to penicillin. (As bacteria have
only one strand of DNA and one copy of each gene, the mutant allele is
expressed immediately and is not masked by a dominant allele.)
– If the population to which the mutant belongs is exposed to penicillin,
the mutant will survive and reproduce whereas those without the mutant
will be killed.

g) Artificial selection
Over the years, humans have used artificial selection to create dog breeds over
the past 150 years or so, humans have been specifically mating dogs that look
a certain way to create the animals we now keep as pests via a process known
as breeding. This is artificial selection, where one species (humans) directs the
traits that get passed down to future generations of another species (dogs).

Application activity 6.2

1) Numerous factors can induce the evolution of species, observe the
diagram below then suggest the cause of the loss of hair.

2) After understanding the evolution, give the factors that are inducing
today’s evolution.

6.3 Speciation

Activity 6.3

1. Observe the diagram below, and write a short notes for your observation

Speciation is the evolution of new species from the existing ones. A species is a
group of organisms with similar features which can interbreed to produce fertile
offspring, and which are reproductively isolated from other species. Organisms
which do not interbreed under normal circumstances to produce fertile offspring
are regarded as reproductively isolated. Mechanisms that prevent the formation

of hybrids are called prezygotic isolating mechanisms, Prezygotic (before a
zygote is formed) isolating. Mechanisms include:
– Individuals not recognizing one another as potential mates or not
responding to mating behavior
– Animals being physically unable to mate
– Incompatibility of pollen and stigma in plants
– Inability of a male gamete to fuse with a female gamete.

The mechanisms that affect the ability of hybrids to produce fertile offspring
are called postzygotic isolating mechanisms. Postzygotic isolating mechanisms
include:
– Failure of cell division in the zygote
– Non-viable offspring (offspring that soon die)
– Viable, but sterile offspring.

The most important isolating mechanism is thought to be geographical isolation,
in which two populations originally of the same species are separated from each
other by a physical barrier such as a mountain, river, or ocean.

a) Allopatric speciation
Allopatric means ‘different countries’ and describes the form of speciation where
two populations become geographically isolated. Geographical isolation
may be the result of any physical barrier between two populations which
prevents them interbreeding. These barriers include oceans, rivers, mountains
ranges and deserts. Which proves a barrier to one species may be no problem
to another. The isolated populations then undergo phenotypic divergence as:
• They independently undergo genetic drift
• Different mutations arise in two populations
• They become subjected to dissimilar selective pressure

b) Sympatric speciation
Sympatric literally means. (‘Same country’) Sympatric speciation occurs when
organisms inhabiting the same area become reproductively isolated into two
groups for reasons other than geographical barriers. Such reasons might
include:
1) The genitalia of two groups may be incompatible (mechanical isolation):
It may be physically impossible for the penis of a male mammal to enter
the female’s vagina
2) The gametes may be prevented from meeting: In animals, the sperm may
not survive in the female’s reproductive tract or, in plants; the pollen tube
may fail to grow.

3) Fusion of the gametes may not take place: Despite the sperm reaching
the ovum, or the pollen tube entering the micropyle, the gametes may be
incompatible and so will not fuse.
4) Development of the embryo may not occur (hybrid inevitability): Despite
fertilization taking place, further development may not occur, or fatal
abnormalities may arise during early growth
5) Polyploidy (hybrid sterility): When individuals of different species breed,
the sets of chromosomes from each parent are obviously different. These
sets are unable to pair up during meiosis and so the offspring cannot
produce gametes.
6) Behavioral isolation: Before copulation can take place, many animals
undergo elaborate courtship behavior. This behavior is often stimulated
by the colour and markings on the members of the opposite sex, the call
of a mate or particular actions of a partner.

Application activity 6.3

1) Which type of speciation is indicated by the diagram below

2) Which of the following is a correct definition of speciation?
a) When one species has a genetic mutation, allowing it to breed with
another species
b) When a species has a genetic defect, making it a brand new species
c) The process by which a species goes extinct, allowing a new species
a chance to live in anew habitat
d) An evolutionary process that leads to the formation of a new species.

3) Which of the following is not true in the formation of a new species?
a) If an isolated population has a new environmental conditions new
traits can be favored eventually leading to the inability to reproduce
with the original population.
b) A mutation causes a population to breed with a different species.
c) Reproductive isolation can occur by the formation of a mountain
range.
d) A population needs to become reproductively isolated.

6.4 Mechanisms of speciation

Activity 6.4

The following image are for two different animals.

a) Write down the similarities and differences in these animals on the
above image.
b) Can you consider them as a single species?

a) Continental drift
The continents which now exist have not always appeared as they do today.
At one time, the earth had a single large land mass called Pangaea. This is
thought to have broken up into two parts, a northern Laurasia and a southern
Gondwanaland. Over millions of years, the two great land masses split up and
moved by a process called continental drift to form our present continents. The

theory that these land masses were once joined is supported by the discovery
in Australia, South Africa, South America, and Antarctica of fossils belonging to
the same extinct species. Fossils in North and South America show differences
between the species, suggesting that these two continents have only joined
together relatively recently. Before this, their fauna (animals) and flora (plants)
were geographically isolated and evolved independently.

Australia shows many excellent examples of species that evolved independently
following its geographical isolation. It is thought that Australia became isolated
about 120 million years ago, when marsupials (mammals without a placenta but
with a pouch in which the young develop) and eutherian mammals (mammals
with a true placenta) diverged from a common ancestor

b) Migration
Migration also called gene flow is any movement of individuals, and/or the
genetic material they carry, from one population to another. Gene flow includes
lots of different kinds of events, such as pollen being blown to a new destination
or people moving to new cities or countries. If gene versions are carried to a
population where those gene versions previously did not exist, gene flow can
be a very important source of genetic variation. In the graphic below, the gene
version for brown coloration moves from one population to another.

c) Divergent evolution
A single species evolves into several new species that live in different ways. The
five of Darwin’s finches are a good example. There are separate species
of finch in the group, all of which probably evolved from individuals belonging to
ne mainland species.

The islands have few other bird species. In the absence of competition, the
finches became adapted to fill all the available niches. In particular, they evolved
a wide range of beak sizes and shapes so that they could take advantage of the
food sources on the different islands. The evolution of an ancestral species into
different species to fill different niches is called adaptive radiation

d) Convergent evolution
Unrelated species independently evolve similarities when adapting to similar
environments

6.1: Table isolating mechanisms

Application activity 6.4

1) Observe the following birds

Observe those figures, what is the type of speciation?
2) Which effect of natural selection is likely to lead to speciation?
a) Differences between populations are increased.
b) The range of genetic variation is reduced.
c) The range of phenotypic variation is reduced.
d) Favorable alleles are maintained in the population.

Skills lab

Formulate models
Camouflage provides an adaptive advantage Camouflage is a structural
adaptation that allows organisms to blend with their surroundings. In this
activity, you’ll discover how natural selection can result in camouflage
adaptations in organisms.

Procedure
Working with a partner, punch 100 dots from a sheet of white paper with
a paper hole punch. Repeat with a sheet of black paper. These dots will
represent black paper.
1) Scatter both white and black dots on a sheet of black paper.
2) Decide whether you or your partner will role-play a bird.
3) The ‘’bird ‘’looks away from the paper, then turns back and immediately
picks up the first dot he or she sees.
4) Repeat step 4 for one minute

Analysis
1) Observe what color dots were most often collected?
2) Infer how does color affect the survival rate of insects?
Hypothesize what might happen over many generations to a similar
population in nature?

End unit assessment 6

1) Name two examples of adaptive radiation.
2) What effect did industrial pollution have on:
a) The frequency of the C (melanic) allele within a population of peppered
moths.
b) The rate of mutation of the c allele to the C allele
3) Explain what is meant by heterozygous advantage, using the sickle-cell
allele as an example.
4) Answer the following questions:
a) Distinguish between homologous structures and analogous structures
with specific examples.
b) Name the type of evolution exhibited by comparing:
i) Flipper of whale and forelimb of desert rat.
ii) Wing of a bat and wing of butterfly
iii) Wing of a flamingo and wing of an insect

Essay questions
1) Explain the various evidences of organic evolution.
2) Explain Darwin’s theory of natural selection. The environment or
nature selects the individual with variations that are favored by the
environment. These compete with the others and able to reach sexual
maturity, reproduce and pass over the favorable characteristics to their
offspring.
3) What do you understand by Lamarckism? How does it differ from
Darwinism?
4) How can you convince that evolution progress?
5) A Darwin and Lamarck contribution to science is unparalleled. Discuss.

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