Objectives
The reader will be able to:
o Explain the term evolution.
o Distinguish between convergent and divergent evolution
o List evidence in support of evolution.
o Describe the various theories of evolution.
Introduction to Evolution
Best Definition for Evolution
Evolution is the process of development of complex organisms from simple forms over a long period of time. It is a very slow process and results in the origin of new species. Scientists have long tried to discover the origin of living organisms. Various observations about the varieties of plants and animals, the diversities in their structures and the reproductive patterns, lead to the concept of evolution. However, the concept of evolution contradicts that of divine creation which stipulates that God created all living organisms. The theory of evolution implies that all living organism, no matter how different, arose from one common ancestor or one living cell.
Types of Evolution
Divergent Evolution
Divergent Evolution is a
type of evolution that produces
different functional structures in organisms that have evolved from a common
ancestor, due to adaptation to environmental changes. In order words, divergent
evolution occurs when two or more closely related species develops into a new
species, by developing different structures to meet the environmental demands.
Divergent evolution could be responsible for the creation of the diversity of
life on earth from the first living cells.
Homologous structures are structures or
organs that have the same evolutionary origin but perform different functions.
Homologous organs show divergent evolution. Example; the wing of a
bat and the arm of a man.
Convergent Evolution
Convergent
Evolution is type of evolution that produces
similar adaptive functional structures in unrelated groups of organisms. In
convergent evolution, unrelated species become more and more similar in
appearance as they adapt to the same kind of environment. For example, the
wings of birds, bats and insects, have different embryological origins but are
all designed for flight.
Analogous structures are structures that
perform similar functions but evolved separately. Analogous organs show
convergent evolution. Example, the wings of insect, bird and bat.
Evidence of Evolution
Fossil Records (Paleontology)
Fossils are
remains or traces of once-living organisms that have been buried and preserved
in sedimentary rock, or trapped in natural asphalt, amber and ice. The remains
of a dead organism may include the entire organism, molds and castes, hard
skeletal structures, petrification, impression, imprints and fecal pellets. The
fossil record contain evidence of how life has changed and evolved throughout
the earth’s history. The fossils in successive strata of rocks show a gradual
change from simple forms to complex forms of life. The geological time scale
explains that the oldest rocks formed show the fossils of simple animals only.
The rocks formed later show more complex forms of living organisms.
Comparative Embryology
Embryology is a specialized branch of biology, which deals with the
formation and development of the embryo. Embryos of many different kinds of animals: mammals, birds,
reptiles, fish, etc. look very similar. At a certain stage of development, they
are fish-like; possess gill slits or cleft in the pharynx and a tail. This
shows that vertebrates descended from aquatic ancestors and therefore passes
through some embryonic stages of its evolutionary ancestors.
Comparative Anatomy
Comparative anatomy is
the scientific study of similarities and differences in the structure of living
things. Comparing the forelimbs of the human, the bat, the bird, and the
alligator all have the same pentadactyl limb plan. The humerus, radius, ulna,
and carpals in each forelimb. Though the limbs look different on the outside,
they are very similar in skeletal structure. More significantly, they are
derived from the same structures in the embryo. This suggests that these
animals evolved from a common ancestor.
Comparative Biochemistry
Biochemistry is the study
of the basic chemical structures and processes that occur in cells. The
biochemistry of all living things shows that all organisms share a common
ancestry. Carbon, Hydrogen, Oxygen and Nitrogen form the three main organic
compounds, Carbohydrates, fats and proteins.
These three organic compounds combine together to form a complex substance
called protoplasm. The protoplasm of all living things, from
amoeba to man, has several similar physical and chemical properties. This
protoplasm is built into structural units of living organisms called cells.
The cells of plants and animals exhibit fundamental similarity in all living
things.
The study of molecules in organisms
also reveals that almost all living organisms have DNA and use the same genetic
code (A, T, G and C). The genetic code for the synthesis of protein is
universal. E.g., the codon UUU in RNA is used to synthesis the amino acid
phenylalanine in all living things, whether Amoeba, Tilapia or human. This is
because they descended from a common ancestor.
Biogeography (Geographic Distribution of Living
Organisms)
The geographical
distribution of various animals is also seen as evidence of evolution. The
differences in various regions on earth cannot be explained by climate alone,
but are evidently the result of a continental drift.
It is thought that at one
time the Americas, Africa, Antarctica and Australia all formed one large
continent called Pangaea. When it split up into the continent we known today,
the various animals evolve independently according to their geographical and climatic
surrounding. Marsupial animals are thought to have developed first in North
America and that they spread from there to Australia and New Zealand through
Antarctica before the continents broken apart. The mammals in South America are
quite similar to those in Africa and it is believed they had common ancestors
before the separation of the two continents.
Vestigial Organs
Some organisms have structures or organs that seem to serve no useful
function. For example, humans have a tailbone at the end of the spine that is
of no apparent use. Some cave-dwelling salamanders have eyes even though
members of the species are completely blind. Such functionless parts are called vestigial
organs or structures. Vestigial organs are often homologous to organs
that are useful in other species. The vestigial tailbone in humans is homologous to
the functional tail of other primates. Thus, vestigial structures can be viewed as
evidence for evolution: organisms having vestigial structures probably share a
common ancestry with organisms in with organisms in which the homologous
structure is functional.
Theories of Evolution
The following scientist were involved in the theory of organic evolution.
□ Jean Baptiste Lamarck’s
□ Charles Darwin
Lamarck’s Theory of Evolution
Lamarck’s theory involves
the inheritance of acquired characters. Theory is resolved into three
components:
□ Influence of the environment
□ Use and disuse of body parts
□ Inheritance of acquired characters
According to this theory,
individuals of the same species growing and developing under different
environmental conditions differ from each other. This means that organism react
to external environmental changes which might give rise to new species.
Example, short necked ancestors of the modern giraffe voluntarily stretched
their necks to reach leaves high in trees during times when food was scare.
Also, animals living in cold environment develops thick fur to survive.
In animals for example
the use, or exercise of certain parts of the body results in the development of
those parts. This means that new characters are acquired in life and can be
passed on to the offspring giving rise to new species. E.g., the development of
the long neck in giraffe. Also, parts of the body which are not used or
exercise might degenerate and disappear or persist as vestiges e.g., the
appendix and coccyx (tail) in human.
This theory made people to start thinking but it was not generally accepted because acquired characteristics are not inherited.
Father of Evolution
Darwin’s Theory
Charles Darwin published
a book “The Origin of Species’’ in
the year 1859. He proposed that the new species came about by a process called
‘natural selection.’
The theory is resolved
into three components:
□ Over-production of offspring and
subsequent struggle for existent among the offspring.
□ Variation of natural population
□ Elimination of unfavorable
variations which results in the survival of the fittest.
According to this theory,
if all the offspring of organisms survive, there will be a geometric increase
in the number of organisms. This will lead to shortage of food supply, water
and space. This would in turn results in struggle for existence due to
competition for the limited resources. There exists variation within species.
Some variations are better suited to the environment while others are not.
Therefore, in the struggle for existence individual with favorable variations
survive. These survivors pass on their character to their offspring.
Individuals with less favorable variations perish. The survivors are better
adapted to their environment. A gradual change of this type may eventually lead
to formation of new species.
Darwin described that
nature selects such organisms, i.e., there is natural selection. Herbert
Spencer referred to this as ‘survival of the fittest.’ Darwin
explained that favorable variations are passed on to the offspring down the
generations. After a certain period of time the organisms appear so different
from the original species that ultimately a new species is evolved.
Alfred Russell Wallace's theory
In 1858, when
Wallace was on a collecting trip in Indonesia, he wrote a 20-page essay
outlining his theory of natural selection and sent it to Charles Darwin. Darwin
almost yielded to Wallace the honor of being the first man to announce the
hypothesis. Darwin and Wallace presented their papers to the Linnaean Society
in London on July 1st 1858. For this reason, many biologists regard both
Charles Darwin and Alfred R. Wallace as joint founders of 'The Theory of
Evolution by Natural Selection'.
SSCE/WASSCE/GCE PASS QUESTIONS AND ANSWERS ON EVOLUTION
OBJECTIVE
1. The theory of natural
selection was developed by
A. Lamarck and
Darwin
B. Darwin and
Wallace
C. Wallace and
Mendel
D. Mendel and Larmack
2. Fossil records found in
sedimentary rocks offer some explanation for the theory of evolution because
A. the deposite have
remains of organisms characteristic of when they were formed
B. different strata
have remains of organisms of the same kind
C. only organisms
with strong parts are fossilized
D. most animal and plant
fossils bear little resemblance to present day living specimens
3. The least evidence in
support of the theory of evolution is provided by the study of
A. anatomy
B. ecology
C. geology
D. embryology
4. From which group of animals
are the mammals generally believed to have most recently evolved?
A. Reptiles
B. Fish
C. Amphibians
D. Birds
5. Long neck in giraffe is
used to illustrate the theory of
A. use and disuse C. origin of life
B. origin of species D. natural selection
6. The natural tendency of
organisms as they evolve is to
A. decrease in size
B. increase in
number
C. develop
specialize structure
D. feed indiscriminately
7. The best explanation for
the theories of natural selection is that
A. all organisms have equal capacity
for survival in their habitats
B. organisms have varying capacities
for survival in their habitats
C. organisms compete for resource and
better competitors survive and thrive
D. habitats allow only organisms that will
not have to compete for survival
8. From evolutionary standpoint, the older a fossil-bearing rocks is,
the more likely it is to contain
A. aves as opposed
to amphibians
B. invertebrates as
opposed to vertebrates
C. angiosperms as
opposed to algae
D. vertebrates as opposed
to invertebrates
9. Which of the following is one of Lamarck's theories?
A. Some variations
are more favourable to existence in a given environment than others
B. All living
organisms are constantly involved in a struggle to existence
C. The size of a
given population remains fairly constant
D. New species originates
through the inheritance of acquired traits
10. The older fossil-bearing rocks, in contrast to the more recent ones,
are more likely to contain
A. animal rather
than plant remains
B. invertebrates
rather than birds
C. flowering plants
rather than mosses
D. reptiles rather than
fishes
11. Darwin is considered the first scientist who correctly explained the
theory of
A. special creation
B. spontaneous
generation
C. use and disuse
D. organic evolution
12. In his theory of evolution, Darwin implied that
A. the struggle for
existence among living organisms is sporadic
B. the most
successful organisms are those that best adapt to their environment
C. organs of the
body which are not regularly used by an organism will disappear
D. any traits acquired by
an organism during its lifetime can be passed on its offspring
13. An argument against Lamarck's theory of evolution is that
A. disuse of body
part cannot weaken the part
B. disused part is
dropped off in the offspring
C. acquired traits
cannot be passed on to the offspring
D. trait cannot be
acquired through constant use of body parts
14. Which of the following requires the use of carbon dating to prove
that evolution has occurred?
A. Comparative
anatomy
B. Biochemical
similarities
C. molecular records
D. Fossil records
15. An evidence of the relationship between living organisms and their
extinct relatives can best be obtained from
A. embryology
B. comparative
anatomy
C. comparative
physiology
D. palaeontology
16. I. Rattus rattus II. Agama agama
III. Bufo regularis IV. tilipia zilli
the order of evolutionary advancement to the above vertebrates is
A. I, II, III, IV
B. I, IV, III, II
C. II, III, IV, I
D. IV, III, II, I
17. An evidence of a common ancestral for fishes, amphibians, reptiles,
birds and mammals is the
A. possession of
wings by birds and bats
B. cold-bloodedness
of fishes, amphibians and reptile
C. presence of gilll
clefts in vertebrate embryos
D. possession of scale by
fish and reptiles
18. The theory which supports the view that the large muscles developed
by an athlete will be passed on to the offspring was proposed by
A. Lamarck
B. Darwin
C. Mendel
D. Pasteur
19. The natural process that produces adaptive evolutionary changes is
A. mutation
B. gene flow
C. genetic drift
D. natural selection
20. According to Darwin, the driving force behind evolutionary change is
A. natural selection
B. genetic drift
C. mutation
D. gene flow
Answers
1. B |
6. C |
11. B |
16. D |
2. A |
7. C |
12. B |
17. C |
3. B |
8. D |
13. C |
18. A |
4. B |
9. D |
14. B |
19. C |
5. A |
10. A |
15. B |
20. A |
THEORY
1.
(SSCE 1993, Q7) Give an account of the
theory of each of the following evolutionists
(i) Lamarck (ii) Darwin
Solution
Refer to notes
2.
(SSCE 2001, Q7) (a) Explain the term
evolution.
(b) Distinguish
between convergent and divergent evolution.
(c) How does
comparative embryology support the theory of evolution?
(d) What are the views of
Lamarck on the theory of evolution?
Solution
(a) Evolution: is the process of development of complex
organisms from simple forms over a long period of time. It is a very slow
process and results in the origin of new species.
(b) Divergent Evolution: is a type of evolution that produces different functional
structures in organisms that have evolved from a common ancestor, due to
adaptation to environmental changes. Whilst
Convergent Evolution: is type of evolution that produces
similar adaptive functional structures in unrelated groups of organisms.
(c) Embryos of many different kinds of animals: mammals, birds,
reptiles, fish, etc. look very similar. At a certain stage of development, they
are fish-like; possess gill slits or cleft in the pharynx and a tail. This
shows that vertebrates descended from aquatic ancestors and therefore passes
through some embryonic stages of its evolutionary ancestors.
(d) Organisms of the same species growing and developing under
different environmental conditions differ from each other. This means that
organism react to external environmental changes which might give rise to new
species. The continuous use of body parts may give rise to new characters or
development of those parts and can be passed on to the offspring giving rise to
new species.
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