Theophilus Sahr Morsay
BIOLOGY
ASSIGNMENT
1. WHAT IS DARWIN'S THEORY OF EVOLUTION?
The theory of evolution by natural selection, first formulated in Darwin's book "On the Origin of
Species" in 1859, is the process by which organisms change over time as a result of changes in
heritable physical or behavioral traits. Changes that allow an organism to better adapt to its
environment will help it survive and have more offspring.
Evolution by natural selection is one of the best substantiated theories in the history of science,
supported by evidence from a wide variety of scientific disciplines, including paleontology,
geology, genetics and developmental biology.
The theory has two main points, said Brian Richmond, curator of human origins at the American
Museum of Natural History in New York City. "All life on Earth is connected and related to each
other," and this diversity of life is a product of "modifications of populations by natural
selection, where some traits were favored in and environment over others," he said.
More simply put, the theory can be described as "descent with modification," said Briana
Pobiner, an anthropologist and educator at the Smithsonian Institution National Museum of
Natural History in Washington, D.C., who specializes in the study of human origins.
The theory is sometimes described as "survival of the fittest," but that can be misleading, Pobiner
said. Here, "fitness" refers not to an organism's strength or athletic ability, but rather the ability
to survive and reproduce.
For example, a study on human evolution on 1,900 students, published online in the
journal Personality and Individual Differences in October 2017 found that many people may
have trouble finding a mate because of rapidly changing social technological advances that are
evolving faster than humans. "Nearly 1 in 2 individuals face considerable difficulties in the
domain of mating," said lead study author Menelaos Apostolou, an associate professor of social
sciences at the University of Nicosia in Cyprus. "In most cases, these difficulties are not due to
something wrong or broken, but due to people living in an environment which is very different
from the environment they evolved to function in."
Origin of whales
In the first edition of "On the Origin of Species" in 1859, Charles Darwin speculated about how
natural selection could cause a land mammal to turn into a whale. As a hypothetical example,
Darwin used North American black bears, which were known to catch insects by swimming in
the water with their mouths open:
"I can see no difficulty in a race of bears being rendered, by natural selection, more aquatic in
their structure and habits, with larger and larger mouths, till a creature was produced as
monstrous as a whale," he speculated.
Theophilus Sahr Morsay
The idea didn't go over very well with the public. Darwin was so embarrassed by the ridicule he
received that the swimming-bear passage was removed from later editions of the book.
Scientists now know that Darwin had the right idea but the wrong animal. Instead of looking at
bears, he should have instead been looking at cows and hippopotamuses.
The story of the origin of whales is one of evolution's most fascinating tales and one of the best
examples scientists have of natural selection.
Natural selection
To understand the origin of whales, it's necessary to have a basic understanding of how natural
selection works. Natural selection can change a species in small ways, causing a population to
change color or size over the course of several generations. This is called "microevolution."
But natural selection is also capable of much more. Given enough time and enough accumulated
changes, natural selection can create entirely new species, known as "macroevolution." It can
turn dinosaurs into birds, amphibious mammals into whales and the ancestors of apes into
humans.
Take the example of whales — using evolution as their guide and knowing how natural selection
works, biologists knew that the transition of early whales from land to water occurred in a series
of predictable steps. The evolution of the blowhole, for example, might have happened in the
following way:
Random genetic changes resulted in at least one whale having its nostrils placed farther back on
its head. Those animals with this adaptation would have been better suited to a marine lifestyle,
since they would not have had to completely surface to breathe. Such animals would have been
more successful and had more offspring. In later generations, more genetic changes occurred,
moving the nose farther back on the head.
Other body parts of early whales also changed. Front legs became flippers. Back legs
disappeared. Their bodies became more streamlined and they developed tail flukes to better
propel themselves through water.
Darwin also described a form of natural selection that depends on an organism's success at
attracting a mate, a process known as sexual selection. The colorful plumage of peacocks and the
antlers of male deer are both examples of traits that evolved under this type of selection.
But Darwin wasn't the first or only scientist to develop a theory of evolution. The French
biologist Jean-Baptiste Lamarck came up with the idea that an organism could pass on traits to
its offspring, though he was wrong about some of the details. Around the same time as Darwin,
British biologist Alfred Russel Wallace independently came up with the theory of evolution by
natural selection.
Theophilus Sahr Morsay
Modern understanding
Darwin didn't know anything about genetics, Pobiner said. "He observed the pattern of evolution,
but he didn't really know about the mechanism." That came later, with the discovery of how
genes encode different biological or behavioral traits, and how genes are passed down from
parents to offspring. The incorporation of genetics and Darwin's theory is known as "modern
evolutionary synthesis."
The physical and behavioral changes that make natural selection possible happen at the level of
DNA and genes. Such changes are called mutations. "Mutations are basically the raw material on
which evolution acts," Pobiner said.
Mutations can be caused by random errors in DNA replication or repair, or by chemical or
radiation damage. Most times, mutations are either harmful or neutral, but in rare instances, a
mutation might prove beneficial to the organism. If so, it will become more prevalent in the next
generation and spread throughout the population.
In this way, natural selection guides the evolutionary process, preserving and adding up the
beneficial mutations and rejecting the bad ones. "Mutations are random, but selection for them is
not random," Pobiner said.
But natural selection isn't the only mechanism by which organisms evolve, she said. For
example, genes can be transferred from one population to another when organisms migrate or
immigrate, a process known as gene flow. And the frequency of certain genes can also change at
random, which is called genetic drift.
A wealth of evidence
Even though scientists could predict what early whales should look like, they lacked the fossil
evidence to back up their claim. Creationists took this absence as proof that evolution didn't
occur. They mocked the idea that there could have ever been such a thing as a walking whale.
But since the early 1990s, that's exactly what scientists have been finding.
The critical piece of evidence came in 1994, when paleontologists found the fossilized remains
of Ambulocetus natans, an animal whose name literally means "swimming-walking whale." Its
forelimbs had fingers and small hooves but its hind feet were enormous given its size. It was
clearly adapted for swimming, but it was also capable of moving clumsily on land, much like a
seal.
When it swam, the ancient creature moved like an otter, pushing back with its hind feet and
undulating its spine and tail.
Modern whales propel themselves through the water with powerful beats of their horizontal tail
flukes, but Ambulocetus still had a whip-like tail and had to use its legs to provide most of the
propulsive force needed to move through water.
In recent years, more and more of these transitional species, or "missing links," have been
discovered, lending further support to Darwin's theory, Richmond said.
Theophilus Sahr Morsay
Fossil "links" have also been found to support human evolution. In early 2018, a fossilized jaw
and teeth found that are estimated to be up to 194,000 years old, making them at least 50,000
years older than modern human fossils previously found outside Africa. This finding provides
another clue to how humans have evolved.
Controversy
Despite the wealth of evidence from the fossil record, genetics and other fields of science, some
people still question its validity. Some politicians and religious leaders denounce the theory of
evolution, invoking a higher being as a designer to explain the complex world of living things,
especially humans.
School boards debate whether the theory of evolution should be taught alongside other ideas,
such as intelligent design or creationism.
Mainstream scientists see no controversy. "A lot of people have deep religious beliefs and also
accept evolution," Pobiner said, adding, "There can be real reconciliation."
Evolution is well supported by many examples of changes in various species leading to the
diversity of life seen today. "If someone could really demonstrate a better explanation than
evolution and natural selection, [that person] would be the new Darwin," Richmond said.
2. WHY ARE LIVING ORGANISMS CLASSIFIED?
A large variety of plants, animals, and microbes found on earth and they differ in size, shape,
colour, habitat, and many other characteristics. So, studying each of them is impossible.
Therefore, scientists have devised mechanisms to classify all living organisms on certain rules
and principles that allow identification, nomenclature, and finally classification of an organism.
3. EXPLAIN THE SYSTEM OF CLASSIFICATION IN DETAIL
There are millions and millions of species, so classifying organisms into proper categories can be
a difficult task. To make it easier for all scientists to do, a classification system had to be
developed.
The evolution of life on Earth over the past 4 billion years has resulted in a huge variety of
species. For more than 2,000 years, humans have been trying to classify the great diversity of
life. The science of classifying organisms is called taxonomy. Classification is an important step
in understanding the present diversity and past evolutionary history of life on Earth.
All modern classification systems have their roots in the Linnaean classification system. It was
developed by Swedish botanist Carolus Linnaeus in the 1700s. He tried to classify all living
things that were known at his time. He grouped together organisms that shared obvious physical
traits, such as number of legs or shape of leaves. For his contribution, Linnaeus is known as the
“father of taxonomy.” You can learn more about Linnaeus and his system of classification by
watching the video at this link.
Theophilus Sahr Morsay
The Linnaean system of classification consists of a hierarchy of groupings, called taxa (singular,
taxon). Taxa range from the kingdom to the species (see Figure below). The kingdom is the
largest and most inclusive grouping. It consists of organisms that share just a few basic
similarities. Examples are the plant and animal kingdoms. The species is the smallest and most
exclusive grouping. It consists of organisms that are similar enough to produce fertile offspring
together. Closely related species are grouped together in a genus.
Linnaean Classification System: Classification of the Human Species. This chart shows the taxa
of the Linnaean classification system. Each taxon is a subdivision of the taxon below it in the
chart. For example, a species is a subdivision of a genus. The classification of humans is given
in the chart as an example.
Binomial Nomenclature
Perhaps the single greatest contribution Linnaeus made to science was his method of naming
species. This method, called binomial nomenclature, gives each species a unique, two-word
Latin name consisting of the genus name and the species name. An example is Homo sapiens,
Theophilus Sahr Morsay
the two-word Latin name for humans. It literally means “wise human.” This is a reference to our
big brains.
Why is having two names so important? It is similar to people having a first and a last name.
You may know several people with the first name Michael, but adding Michael’s last name
usually pins down exactly whom you mean. In the same way, having two names uniquely
identifies a species.
Revisions in Linnaean Classification
Linnaeus published his classification system in the 1700s. Since then, many new species have
been discovered. The biochemistry of many organisms has also become known. Eventually,
scientists realized that Linnaeus’s system of classification needed revision.
A major change to the Linnaean system was the addition of a new taxon called the domain.
Adomain is a taxon that is larger and more inclusive than the kingdom. Most biologists agree
there are three domains of life on Earth: Bacteria, Archaea, and Eukaryota (see Figure below).
Both Bacteria and Archaea consist of single-celled prokaryotes. Eukaryota consists of all
eukaryotes, from single-celled protists to humans. This domain includes the Animalia (animals),
Plantae (plants), Fungi (fungi), and Protista (protists) kingdoms.
This phylogenetic tree is based on comparisons of ribosomal RNA base sequences among living
organisms. The tree divides all organisms into three domains: Bacteria, Archaea, and Eukarya.
Humans and other animals belong to the Eukarya domain. From this tree, organisms that make
up the domain Eukarya appear to have shared a more recent common ancestor with Archaea than
Bacteria.
