CHAPTER 16-
THE
PROCESS OF
EVOLUTION

HOMOLOGY AND
EVOLUTION
Homology is the existence of shared ancestry between a pair of
structures, or genes, in different taxa. A common example of
homologous structures is the forelimbs of vertebrates, where
the wings of bats, the arms of primates, the front flippers
of whales and the forelegs of dogs and horses are all derived from
the same ancestral tetrapod structure.
Evolutionary process is not a haphazard event in nature that
simply happened in a short period of time. Evolution is almost
close to the concept of change.
To evolve means to change. This change, however, is not on the
individual species but on the population.
A lot of people find it hard to embrace the concept of evolution
because they believe that it is opposed to their faith especially on
the concept of creation.

 The limbs are shaped differently
because their lifestyles’ or how they
live are different from one another.
What is interesting, however, is that
their forelimbs, have the same set of
bones.
 The limbs of animals called tetrapodor
animals with four legs. However, not
all tetrapods have four legs. Tetrapods
also include animals without four feet
such as whales and snakes.
 They used to have limbs but have lost
their them as they migrate or return to
water and stayed there for some time.
 Whales bones unearthed in excavation
sites in Pakistan and Egypt showed that
ancient whales used to have four limbs
but eventually lost two of them
specifically their hind legs. The front
legs are now flippers.

 Amphibians, reptiles, and mammals
are classified as tetrapods. Humans
are classified as tetrapods although
we walk with only two legs. The
ancestors of present-day tetrapods
lived in the water. What is surprising
is that they evolved from finned
organism.
 Homology simply indicates that
although organism or animals are
totally different, they have certain
traits common to all of them inherited
from a common ancestor.
 They became totally different today
from what they were before because
they have evolved. Homologous
structures are not only common in the
animal kingdom;

 The leaves of these plants are not the typical green leaves we
see around us. Their function is not basically to perform
photosynthesis but either to provide the plant with nutrients
which the soil cannot provide or inadequately cannot give.
Pitcher plant and the venus flytrap are carnivorous plants. They
‘eat’ insects. Poinsettia’s bright read leaves are called bracts to
attract pollinators. The prickly spines of cacti are modified
leaves to give them protection from animal predators and to
shade them from heat. The shape and function of each plant in
is different, yet, they are all leaves modified to help the plant
adapt and survive their own unique environment. Modified
leaves in plants are example of homologous structures.

FOSSIL RECORDS AND
EVOLUTION
Some of the ratites. They are found in South America,
Africa, Australia, Papua New Zealand. Like present-day
birds are sometime called avian dinosaurs. Scientifically
speaking, birds are reptiles.

 It is interesting to know that the very first
commercial ostrich farm in the country is
located in Cagayan De Oro. It first
opened in 1996 with just three pairs of
breeding ostriches imported from
Australia. The meat and egg of ostriches
very high in protein but low in cholesterol
compared to chicken.
 Elephant birds are the largest bird that
ever lived on Earth. They stand 10 feet
tall and weigh more than 450 kilograms.
 Elephant birds roamed Madagascar 60
million years ago during the time when
birds ruled the Earth. They have strong
and massive legs, long claws, and
powerful neck. Their eggs which are
about 170-200 times bigger than the
chicken eggs, enough to feed a family for
a day, were hunted for food (Extinct
Animals, 2015).

Marco Polo once wrote of a giant bird he saw in the late
13th century. Elephant birds existed until the 17th century.
Their extinction was attributed to human activity.
Collectively called ratites, elephant birds, like ostriches,
rheas, kiwis, and all other birds, evolved from a two-legged
carnivorous dinosaurs called therapods during Late
Jurassic Period (University of California Museum of
Palaeontology, n,d; Sanger, 2015). Two of the well-known
members of the therapods are the towering Tyrannosaurus
rex and the velociraptors.

The existence of T. Rex, velociraptor, and other dinosaurs were
proven by the discovery of their fossil remains. T. Rex fossils were
discovered in places like Alberta, Canada and Texas (Castro 2016).
The first velociraptor fossil was found in Gobi Desert, Outer
Mongolia in 1923 by Peter Kaisen of the American Museum of
Natural History (Castro, 2016).

 The bones of the chicken is smaller and
are proportioned to its size whereas the
bones of Allosaurus are thicker and
shorter to support its size.
 Evolutionary biologists established that
the transformation (evolution in terms of
size and appearance) of the dinosaurs to
modern day birds did not occur in a snap
but gradual. Changes in features happen
one at a time (Sanger, 2015).
 Sanger (2015) described the transition as
“first bipedal locomotion, then feathers,
then a wishbone, then more complex
feathers that look like quill-pen feathers,
then wings.” Dinosaurs first transformed
into a sparrow-size prehistoric bird called
IBEROMESORNIS.
 Fossil remains of Iberomesornis are found
in Spain. According to www.prehistoric-
wildlife.com. (n.d), Iberomesornis ) “are
considered to represent an intermediate
stage in bird evolution before the
appearance of,? More advanced forms
closer to modern birds”

EXTINCTION OF
SPECIES
 Everyday, a new species of plants or animals is being discovered. However,
the sad part is many are disappearing faster before they can be studied in
Science
 You might have heard of Charles Darwin and how his historic five-years
voyage aboard HMS Beagle including his visit to the island of Galapagos
helped him formulated his theory of evolution.
 His book Origin of Species contains his thoughts on evolution., and for this,
Darwin is regarded today as the Father of Evolution.
 Extinction is a serious threat to the perpectuation of life. It is not just an
environmental problem confined in one location or in several locations in this
planet.
 It is a social problem that threatens our survival as human being because life
on Earth is interconnected.
 An invisible thread connects all creations on this beautiful planet. Everything
is affected whenever one species vanished from the face of the Earth. When a
species become extinct, it goes with it its own gene pool which is lost forever.

DARWIN’S VOYAGE AND ON THE
ORIGIN OF SPECIES AND THEORY
OF EVOLUTION
 Have you ever wondered how Darwin came up with his grand theory of
evolution? Or what shaped his idea on evolutionary by natural selection?
 Great ideas are always inspired by the things we see around us by own
experiences. Sometimes, our ideas are influenced by what we read or hear.
In his case, Darwin was heavily influenced by the things he saw on his five-
year trip.
 It should be emphasized that Darwin had already conceptualized the idea of
evolution by natural selection long before joining the trip.
 For Darwin, a naturalist, the distillation of his idea on evolution by natural
selection is a product of so many things, foremost of which is his visit in the
Galapagos Island aboard HMS Beagle, already on its second expedition.
 Darwin was only 22 at that time when he was selected to join and a fresh
graduate from Cambridge. His task, as a naturalist was to collect samples of
plants and animals, including rocks.

THEORY OF EVOLUTION
BY NATURAL
SELECTION
Darwin’s ideas on evolution are extensively explained in his book
“On the Origin of Species” published in 1859. His ideas created a
lot od controversies especially with the religious authorities who
found his views in conflict with the Bible on the idea of creation.
The fundamental tenet of Darwin’s idea is that all the different
species have evolved from simple organisms and that include
humans.
The first life, which is a single-celled organisms, evolved more
than 3.5 billion years ago or about 1.5 billion years after the Earth
was formed.

NATURAL SELECTION
IN ACTION
 The theory of evolution states that evolution happens by natural selection.
The concept of natural selection is very important in understanding evolution.
 It is one of the basic mechanisms answer the question “How organism
evolved?”
 Nature, select the traits that have the best chance to survive and reproduce.
These traits are encoded in their genes and are transmitted from one
generation to another, that is, they are inheritable. Natural selection is nature’s
gatekeeper or control quality mechanism.
 The heritable trait is fur color. This is encoded in the genes, is transmitted
from generation to generation. Heritable trait increases fitness. It enables the
organism to survive and reproduce. Heritable trait like fur color that increases
fitness called adaptive heritable trait. Adaptive heritable traits are important
in natural selection.


AND ORIGIN OF
SPECIES
 The formation of different species of honeycreepers is an
example of adaptive radiation, a rapid evolution wherein several
new species is created from a founder species in a short period
of time.

SPECIATION
 Study the figure. It is phylogeny that shows a polytomy. A polytomy is a
node where several descendants emerge from a single ancestor. Whenever
a phylogenetic tress shows a polytomy or polytomies, it conveys two
things; available data are not sufficient to explain how it gave rise to
several descendants or it is possible that a simultaneous speciation occurs
among descendants. The case of honeycreepers is an example of a
phylogeny showing polytomy.
 Speciation describes how a new kind of plant or animal species is created.
It occurs when a group within a species separates from other members of
its species and develops its own new and distinct species is formed in the
course of evolution.
 To better grasp the concept of speciation let us first define the term
species. A species is the basic category of biological classification. It
refers to a group of organisms or individuals that actually or potentially
interbreed in nature, This definition is totally different from the typical
definition that defines species as;
 “Composed of related individuals that resemble one another, are able to
breed among themselves, but are not able to breed with members of an
other species”.

 There are five types of speciation in nature; allopatric, peripatric, and
sympatric and artificial.
1. Allopatric speciation – occurs when members of a species are
separated into two groups due to physical barriers.
2. Peripatric speciation – occurs when small groups of individual in a
population separate from the larger group and form a new species
3. Parapatric speciation – occurs when a species occupies a large
geographic area.
4. Sympatric speciation – occurs due to reproductive isolation.
5. Artificial speciation – occurs when human beings intervence in the
natural reproduction using techniques or technology to create new
species specifically for economic benefits.

EXTINCTION OF
SPECIES
 Dinosaurs appeared 230 million years ago and ruled the earth for more than
135 million years. It was Richard Owen who first introduced the term
dinosaur in 1842. The term is derived from two Greek words deinos, which
means “terrible” “fearfully great,” and sauros, meaning “lizard” or reptile
(Gammon, 2016)
 Dinosaurs, the largest land animals that ever roamed the Earth, became extinct
65 million years ago. Everything we know about them was derived from the
analysis of their fossils found in different parts of the world. Palaeontologists
unearthed complete bones of heses reptiles in good condition giving us a good
picture of how they looked like and lived. Dinosaurs are not the only extinct
animals on Earth, there are many more including plants and other organisms.

EXTINCTION Extinction is a serious ecological problem. The extinction of one species
affects the rest of ecosystem because all creation are interconnected by an
invisible thread of life. Extinction means end of the species. It occurs when
the last member of the population dies.
 A species is said to be extinct when no member of the species remains alive
anywhere in the world. A species said to be extinct in the wild if the only
surviving member is in captivity. A captive species is usually found in
research of breeding centers.
 On one hand, a species is said to be locally extinct or extirpated if it is no
longer found in the area where it used to live and is found somewhere else.
The species outside its natural habitat.
 Darwin argued that extinction is a natural phenomenon as a consequence of
evolution. According to him, extinction occurs whenever organisms fails to
adapt to the changing and water.
 This is true for normal process of extinction or natural extinction process.
Causes if natural extinction process are demographic failure or genetic
swamping, speciation or anagenesis. Anagenesis oranagenetic evolution is
evolution within a lineage. It refers to the collective changes that transform
one species into a different species with different characteristic. The increase
in cranium size of humans is an example of anagenetic evolution.

CAUSES OF NORMAL
PROCESS OF
EXTINCTION
 The Earth has already experienced five main mass extinction events. Mass extinction
is a rapid geologic even that takes place in a few million years. It occurs when at least
half of all species die in a short period of time due to a catastrophic event like
massive earthquake, comet and asteroid bombardments, glaciation, sudden global
temperature change, or disease.
 The largest mass extinction occurred 250 million years ago with 95% of all species
were extinct. During mass extinction, old species are replaced with a new one.
 Mass extinction is supported by fossil records. Palaeontologists at the American
Museum of Natural History observed “fossils that are abundant in earlier rock layers
are not present in later rock layers.”
 A wide range of animals and plants suddenly died out, from tiny marine organisms to
large dinosaurs. The sudden demise of dinosaurs of the Cretaceous-Tertiary
extinction event (K-T event) that happened 65.5 million years ago, is an example of
mass extinction.
 Mass extension should not be taken negatively. It is a normal cycle of life in this
planet. Mass extinction causes new life forms to emerge. For instance, the mass
extinction of dinosaurs allowed mammals to diversity and evolve.

EXTINCTION
EVENTS
 Palaecontologists recognize five main extinctions events, also known as the Big 5
1. The late Ordovician event 348 million years ago, when 100 families went
extinct.
2. Late Devonian event 360 million years ago, when 30% of families went extinct.
3. End Permian event 245 million years ago, the biggest extinction of all the time
when over 50% of all families were lost.
4. Late Triassic event 35% of families died out.
5. The Cretaceous Tertiary (K-T) event 65 Million years ago, which ended the reign
of the dinosaurs.

SIXTH MASS
EXTINCTION
 Scientists anticipate another mass extinction and call it the sixth mass
extinction in the history of planet Earth. This expected mass extinction is
being caused by destructive human activities (destructive fishing, land
clearing, pollution, mining, etc) and uncontrolled population growth.
 According to International Union for Conservation of Nature, destructive
human activities have caused extinction of about 514 animal species since
the beginning of the 15th century. It is during this period that Industrial
Revolution started.
 Extinction of plants and animals has irreversible consequences to humans.
The potential of this organism as possible source of medicine for dreaded
forms of cancer, hypertensions, kidney failure, depression, fever, etc., is
forever lost.

 Complete extinctions of plants in the rainforest is a serious environmental
problem with huge social implications.
 Marine organisms also face threat of extinction brought by destructive human
activities. Our reliance on fossil fuels contributes to ocean acidification which
has serious effects on marine organisms. For instance, coral bleaching is
attributed to ocean acidification. As the ocean slightly becomes more acidic,
the ability of shell-forming marine organisms like corals, oysters, shrimp,
lobster, scallops, clams, and many planktonic organisms, and even some fish
species is affected.
 Ocean acidification also effect the size of shelled organisms, for instance,
clams grow smaller. The rate of extinction of marine organisms is almost
similar to the rate of terrestrial extinction. Signs that marine extinction is
gaining ground are: decline in abundance of marine vertebrates of 22%
decline in marine fishes by 38% and decline in population of baleen whales by
80 to 90%.