Biology Form Four Notes – Evolution

Concept of Organic Evolution

Evolution is the gradual development of organisms from simple form to more complex forms over a long duration of time. Evolution is marked by emergence of new species from pre-existing species and the disappearance of some species. The species that disappear are said to become

extinct. Key terms used in organic evolution

Carbon dating: This is a method of estimating the ages of dead materials of biological origin

Natural Selection: This is selective force occurring in nature, which is responsible for

eliminating the unfavourable traits to retain only favourable traits in the population.

Specie: These are organisms, which have ability to interbreed freely to produce fertile off springs.

Fossils: These are the remains of organisms that lived in the past, preserved naturally in rocks, peat or ice.

Importance of Studying Evolution

It helps to understand the biological forces that cause organisms to develop from simple to more complex organisms to the extent of new species emerging It helps to know how different organisms relate

Theories of the Origin of Life

The basic ideas about the origin of life Outline the basic ideas about the origin of life The origin and diversity of life is based on the contribution of theologists, philosophers and

scientists. Early scientists put forward theories, which suggested that life originated from non-

living matter. However changes in climatic conditions, habitats and complexity of living

organisms contradicts these suggestions.

Modern scientists put both theories, which suggest that the origin and diversity of life was brought about by the process of evolution. Two of the most well known of evolution scientists

are: Jean Baptiste Lamarck

Sir Charles Darwin

The theories of the Origin of Life

State the theories of the origin of life There are numerous theories of evolution that try to explain the origin of living things. The main

theories of the origin of life are:

Theory of Special Creation Theory of Chemical Evolution Theory of Spontaneous Generation

Steady State Theory The Theory of Special Creation

According to this theory life was non-existent before a particular time. Then the Supreme Being

(Supernatural power) created all living things and there was life on Earth from then henceforth

This theory proposes that differences and similarities between organisms are as a result of how the organisms were created. Major religions like Christianity, Islam and Buddhism have theories that support special creation. The theory of fixed status and catastrophism was put forth by Cuvier to support the religious point of view. According to Curvier, fossils were brought about by catastrophes such as floods as outlined in the holy bible. During the floods the earth's surface

was deformed and many creatures were killed and covered by a mass of land

The Theory of Chemical Evolution

According to this theory, about 13.7 billion years ago, a cosmic explosion occurred and the universe has since been expanding and cooling. Before the explosion, the earth was very

compact, dense and hot.

The formation of the universe created condition like high ultraviolet radiation and high temperatures. The gaseous composition was different from todays. The universe cooled and protons combined with electrons to form hydrogen atoms, which were the first atoms to be

formed

Hydrogen combined chemically with other elements to form compounds such as water, hydrogen

is present in almost all organic compounds.

This theory was advanced by Alexander Oparin in 1923, he stated that in the beginning the atmosphere contained ammonia, carbon dioxide, helium, hydrogen and methane but lacked oxygen. The compound was a result of high temperature, ultraviolet radiation and electrical

discharge that were plentiful after cosmic explosion.

The compounds were dissolving in rainwater to form nutrient both (a mixture of organic compound in water that accumulated in the water bodies on the earth's surface), The simple compounds combined to form complex substances, using energy from the high temperature and ultraviolet rays later polymers such as proteins lipids and carbohydrates were formed. The first

single-celled organism arose from these polymers.

The formation of ribonucleic acid (RNA) a self-replicating molecule was a pre-requisite to life as the form could replicate itself. Living organisms could reproduce themselves. The first life forms were heterotrophic using the compound in the nutrient broth as food. The organisms reproduced by budding

The Theory of Spontaneous Generation

Aristotle advanced the theory of spontaneous generation and it dates back to the 4* Century. The

theory was applied up to the 19" Century but it is no longer applied. The scientists believed that

simple organisms like worms and frogs could arise from mud, dust or rotten food. That means

life can originate from non-living matter e.g. maggots can arise from rotten meat.

The Steady State Theory

This theory was popular during the 1950s and 1960s, before its demise in the late 1960s. According to these theory the universe has always existed and has no origin that is it did not have

a moment of creation this life has no origin

Cosmozoan Theory

Also this theory states that or suggests that life on earth originated from elsewhere. In eighteenth century scientists questioned these steady state and Cosmozoan theories due to the presence of

fossils and emergence of new species

Theories of Organic Evolution , Lamarckism

Lamarck's theory of Evolution

State lamarck's theory of evolution

Darwin was not the only person to develop a theory of evolution. Jean-Baptiste Lamarck was a French scientist who developed an alternative theory at the beginning of the 19th century. His

theory centred on two ideas:

the law of use and disuse the law of inheritance of acquired characteristics His theory stipulated that a characteristic which is used more and more by an organism becomes

bigger and stronger. One that is not used disappears eventually. Any characteristic of an

organism that is improved through use is passed to its offspring.

Lamarck's Observations and Deductions

Explain lamarck's observations and deduction

Jean Baptiste Lamarck was a French naturalist. Lamarck formulated a theory on evolution after

studying botany and the fossils of marine invertebrates.

He used the law of use and disuse which explains that organism enhanced certain abilities by exercising them and lost other abilities through disuse example the ancestors of the present day long necked giraffe. These early giraffes fed on short plants when the short plants became scarce the giraffe had to stretch their necks to feed on taller plants. Thus their necks became longer. The longer necks were passed onto their offspring hence after a long time giraffe developed the long

necks they have today.

His theory was based on inheritance of acquired characteristics the offspring then adapt further,

advancing evolution of the species.

Merits and Demerits of Lamarck's Theory of Evolution Outline merits and demerits of lamarck's theory of evolution

The Merits of Lamarck's Theory of Evolution include: Lamarck theory lead to further studies on evolution of species

It gave rise to discovery of genes and genetics which is now widely used in many fields of

biology

Upon rejection of his theory Lamarck decided to study about invertebrates which made great

contribution in development of Zoology

Darwinism

Darwin's Theory of Evolution

e Darwin's theory of evolution Charles Robert Darwin (1809 — 1882) was an English naturalist. He based his theory on

observation made during a five-year geographical study

Darwin's main observations were:

Every generation of organisms have more off springs than parents. However, the number of adult organisms remains generally stable from generation to generation. Therefore is a struggle for

existence that causes many off spring to die before becoming adults

There are many variations in a species. Variations are passed from parents to their off spring. Advantageous variations enable survival in the environment organism with disadvantageous

variation due. This is called survival of the fittest.

Off springs with favourable variations grow into adults and reproduce therefore favourable variations accumulated in the species; enabling adaptation to the environment, this gives rise to

new specie.

A change in the environmental conditions favours other characteristics of the organisms. The effect of these changes on the organisms is that other features become more prominent than

before resulting in evolution Merits of Darwin's theory

The theory enabled scientists to carry further studies, leading to new discoveries that suggest the

origin of life

Helped scientists to understand about drug resista ind evolution of germs like bacteria and

viruses leading to new strains

Enable further research to find cure or vaccines of germs, bacteria and viruses

Shortcoming of Darwin's Theory:He failed to explain how variations in populations arose and

were maintained from one generation to the next.

Evidences and application of Organic Evolution in the Real Life Situation

Investigate evidences and application of organic evolution in the real life situation Scientists can prove that evolution has taken place by various methods. Some of these methods

are

Comparative anatomy:Comparative anatomy is the study of biological structures in different

organisms. The scientists look at structures that are similar in different organisms or species.

Example limbs of vertebrates such as human beings, goats and wings of birds are used for different purposes but they have a basic design structure, this is known as homologous structure.Example fore limbs of humans are for manipulation, fore limbs of birds (wings) are for flight and fore limbs of a goat are for walking; this shows that all these animals are from common ancestors. Analogous structures are the ones, which look different, but they perform similar functions e.g. insect, birds and bats all have wings used for flight but they have different

structural organization.

Fossil records:Fossils are remains of organisms that lived in the past preserved naturally in rocks or on ice. The study of fossils is known as paleontology when fossils are dated scient can estimate the age of that organism. Method used by scientists to know the age of fossils is

carbon dating using isotope of Carbon 14

Embryology:In comparative embryology embryos of different vertebrates at early stages are compared and they are seen to have resemblances. Species that show similar embryonic

development are assumed to be closely related although the adult may be quite different

Natural Selection in Action:Nature led to the selection of a genetic combination that resulted in a more frequent melanic variety compared to the non-melanic variety. Before the industrial

revolution in Europe the white variety of moth was more prevalent. Industrialization in Europe in

the 18" Century polluted the environment, burning of coal released a lot of soot and smoke.

These pollutants coated tree trunks, killing the lichens that grew on the tree trunks. The colour of the tree trunks became black; this camouflaged the dark melanin form of the peppered moth. The

predators of the moth did not feed on many dark moths because they were not very visible.

Evidence from vestigial organs:These are structures, which have been greatly reduced and ceased to be functional. Presence of vestigial organs is an indication that they existed in ancestral forms but as a result of evolution such structures have been so much reduced to the extent of loosing or greatly changing their original function. Examples of vestigial structures are wings of

flightless birds such as ostriches and penguins.