Evolution by Natural Selection

Question 1

Hypothesis

Answer 1

Scientists put forward one or more possible explanations for their observations, and design and carry out investigations to test whether their “possible explanations” are correct or not. These “possible explanations” are called hypotheses (singular hypothesis).

Question 2

Theory

Answer 2

When scientists use the word “theory” they are referring to an explanation for something that has been observed in nature which can be supported by facts, generalizations, tested hypotheses, models and laws.

Question 3

What is Evolution

Answer 3

Biological Evolution is a special type of evolution that refers to changes that living things have undergone over long periods of time.

Question 4

Meaning of Biological Evolution

Answer 4

All present day life forms have descended from and are related to those that lived in the past.
All present day life forms may look different from those that they descended from because they because modified from one generation to another.
That is why the theory of evolution is also referred to as the theory of “descent with modification”.

Question 5

What we already know about the Diversity of Life and Evolution

Answer 5

According to scientists, evolution of the major taxa took extremely long periods of time. Therefore, they established a time scale that goes beyond seconds, minutes, hours, days, weeks, months, years, decades, centuries and millennia, that we are familiar with today. This is known as the Geological Time Scale.

Question 6

Variations within a species

Answer 6

The word ‘species’ to a group of similar organisms that are able to interbreed to produce fertile offspring.
The word ‘population’ refers to organisms of the same species, occupying same habitat at the same time, and having the ability to interbreed.
Variation refers to the small differences that exist between individuals of a species or population.

Question 7

Sources of variation

Answer 7

Mutations: Mutation involve a change to the structure of a gene. This leads to an altered genotype resulting in a different or altered phenotype.

Question 8

Variation as a result of meiosis is due to

Answer 8

Crossing Over
Random arrangement of chromosomes
Random fertilization of gametes

Question 9

Continuous Variation

Answer 9

In continuous variation, there are a range of different phenotypes for a particular characteristic. For example, if we measure the height of all the learners in your school.
Continuous Variation is brought about by many genes working together i.e. it is an example of polygenic inheritance.

Question 10

Discontinuous Variation

Answer 10

In discontinuous variation, there is no range of different phenotypes for a particular characteristic. Blood groups are a good example.

Question 11

Evidence from Paleontology

Answer 11

Paleontology is the study of fossils. Fossils are the remains of ancient life forms preserved in the rocks, although fossils have also been found in ice, tar and the dried sap of trees.

Question 12

Relative Dating

Answer 12

In relative dating, the age of a fossil is worked out by trying to find out how it is related to the age of another fossil or geological event. Such as a volcanic eruption. Relative dating, can only tell us whether a particular fossil was formed before or after another fossil or geological event, it cannot be used to find out the exact or even approximate age of a fossil.

Question 13

Radiometric Dating

Answer 13

Radiometric dating, attempts to find out how long ago a particular fossil was formed. Radiometric dating attempts to answer the question, ‘How many years ago was this fossil formed’?

Question 14

Interpretation of the Pre- Cambrian times

Answer 14

The earth is about 4.5 billion years old.
The first life forms (the Prokaryotes) developed on Earth about 3.8 billion years ago and they existed in the oldest rock forms.
Life forms in existence today are more complex than any of those that lived in the past, and they occur in more recent rocks.
Most of todays life forms are different from the fossils of ancient life, for example, fossils of the first horses indicates they were as small as foxes, but later fossils showed a gradual increases in size to the present-day forms.
Many of the life forms that existed in the past are no longer in existence today, they have become extinct.

Question 15

Evidence from Comparative Anatomy/ Modification by Descent

Answer 15

Charles Darwin interpreted the structural differences of the forelimbs of different mammals, all built on the same basic plan, in the following way:
The forelimbs of all mammals arose from that of a common ancestor in which the forelimbs had the same basic plan.
These structures now show variations (differences) because they became modified to perform different functions.
This is referred to divergent evolution.
He explained further that the pattern, or basic plan, would not have been the same in all these mammals if these structures developed independently in each animal.

Question 16

Structures in different species that are similar to each other

Answer 16

Structures in different species that are similar to each other because they arose from a common ancestor are referred to as homologous structures.

Question 17

Adaptive radiation

Answer 17

Scientists interpret the pressure of homologous structures to mean that all the species which show homologous structures have arisen from a common ancestor which become adapted to live in different environments. This is known as adaptive radiation.

Question 18

Evidence from biogeography

Answer 18

Sometimes two two similar ecological niches in different parts of the world may show some similarities. Darwin explained that these similar structures have evolved independently from ancestors ancestors. This is called convergent evolution.

Question 19

Analogous structures

Answer 19

Similar structures that have come about by convergent evolution from different ancestors are called analogous structures.

Question 20

Evidence from Molecular Biology and Genetics

Answer 20

Identical DNA Structure
Similar sequence of Genes
Similar Portions of DNA with No Functions
Identical Protein Synthesis and Similar Proteins.
Similar Respiratory Pathways.

Question 21

Evidence from Comparative Embryology

Answer 21

Comparative Embryologists study the similarities and differences in the way organisms develop. They examine patterns from the early stages of development of an organism, known as an embryo, to the fully grown organism.

Question 22

Theory of recapitulation

Answer 22

Darwin’s followers have used these observations to develop the theory of recapitulation. According to this theory, the embryo of an organism during its development, passes through the adult stages of all its ancestors.

Question 23

Origins of Ideas about Origins

Answer 23

Erasmus Darwin, the grandfather of Charles Darwin, felt that all forms of life had descended from a single filament of spermatozoa.

Question 24

Lamarckism

Answer 24

Lamarckism is the idea that an organism can pass on characteristics that is acquired during its lifetime to its offspring. It is named after the French biologist Jean-Baptiste de Lamarck (1744-1829).

Question 25

According to his law of use and disuse

Answer 25

Organs became modified or adapted according to how frequently they were used.
If they were used more frequently it became bigger, stronger or changed so that it could work better.
On the other hand if an organ was disused, it became smaller until it totally disappeared.

Question 26

According to his law of inheritance or modified/ acquired characteristics

Answer 26

The modifications brought about by the frequently of use or disuse were able to be transmitted to the offspring.

Question 27

Today, Lamarck’s theory is rejected by most biologists since they say that

Answer 27

Organisms evolved, not because they wanted to evolve, instead these changes took place randomly, in response to the environment.
There is very little evidence to support Lamarck’s idea that change brought about by adaption to the environment are inherited from parent to offspring.

Question 28

Darwinism

Answer 28

Darwinism is a theory that explains the evolution of new species through natural selection.

Question 29

Observations on which Darwin based his theory of evolution by natural selections

Answer 29

5 Main observations:
Variation
Offspring
Competition
Genetics
Natural Selection

Question 30

Darwin’s theory of Evolution by Natural Selection

Answer 30

Plants and animals generally produce a large number of offsprings.
The offsprings of plants and animals of the same species show a great deal of variation.
The offspring produced compete with each other for available resources.
Only those individuals with favourable characteristics (enabling them to compete successfully for resources or adopt to changing environmental conditions) will survive.
Darwin called this natural selection.
In the next generation there would be larger proportions of individuals with favourable characteristics.
As natural selection occurs from generation to generation, there is therefore a continual, gradual change in populations, leading to the evolution of new species.

Question 31

Gradualism

Answer 31

According to Darwin’s theory, evolution occurs gradually and uniformly over long periods of time. Therefore, Darwin’s theory is sometimes referred to as phyletic gradualism or simply gradualism.

Question 32

Punctuated Equilibrium

Answer 32

In 1972, paleontologists Niles Eldredge and Stephen Jay Gould published their theory called punctuated equilibrium. According to this theory, most species do not undergo any change for long periods of time. Then suddenly, the species undergo rapid change over a short period of geological time, resulting in new species.

Question 33

According to the theory of punctuated equilibrium

Answer 33

A long time ago, there were a lot of tiger like animals, but without stripes.
Then suddenly, a mutation occurred in a few of the animals, causing a huge change, they were born with stripes.
The stripes helped the tigers to camouflage themselves amongst grasses and trees.
More of the striped tigers survived than the un-striped ones.
The striped tigers lived to reproduce and their offspring also did very well.
Over only a few generations, the whole population was born striped.

Question 34

According to the theory of gradualism

Answer 34

At first, the entire population of tiger-like was unstriped
A few of the tigers developed marks on their fur, as a result of mutations.
Since these marks helped them to camouflage, more individuals with marks survived than those without marks.
Over a long period of time more and more individuals with marks survived from generation to generation
At the same time, the marks gradually became clear stripes.
Eventually, the entire population of tiger-like animals became striped.

Question 35

Artificial Selection

Answer 35

Artificial selection is a scientific teem used to describe the breeding of plants and animals for desirable characteristics and not necessarily those that would allow the offspring to survive better in the wild. Since particular desirable characteristics are selected, it is also known as selective breeding.

Question 36

Difference between Artificial selection and Natural Selection

Answer 36

Artificial Selection is similar to natural selection except that, whereas in natural selection the characteristics similar are those that are best suited to the environmental conditions, in artificial selection humans determine which characteristics should be selected.

Question 37

Species

Answer 37

A Species refers to a group of similar organisms that are able to interbreed to produce viable offspring which are fertile.

Question 38

Population

Answer 38

A population refers to organisms of the same species occupying the same habitat at the same time, and having the ability to interbreed.

Question 39

Speciation

Answer 39

Speciation refers to the formation of new species.

Question 40

Allopatric Speciation

Answer 40

New species my be formed when a population becomes separated into two sub-populations by a geographic barrier/ isolation such as mountain or river. Each sub-population then develops into a new species. This is called allopatric speciation.

Question 41

Sympatric speciation

Answer 41

New species may be formed without the presence of a geographic barrier/ isolation to separate the population into two sub-populations. The two or more groups formed within the population develop reproductive barriers which prevent them from interbreeding resulting in separate species. This is called sympatric speciation.

Question 42

Speciation by Geographic Isolation (Allopatric Speciation)

Answer 42

Sometimes a large population, showing a great deal of variation may become separated by a geographic barrier.
The two populations are no longer able to mix.
Each population reproduces separately and undergoes natural selection independently according to its own environments.
The two populations become genotypically and phenotypically different from each other.
These differences may prevent them from interbreeding, even if they are allowed to mix.
One or both populations may become a new species.

Question 43

Mechanisms of Reproductive Isolations

Answer 43

Habitat Isolations.
Temporal Isolation.
Species-specific Courtship Behaviour.
Adaption to different Pollinating Agents.
Prevention of Fertilisation.
Hybrid - Infertility.