ATS COACHING CLASSES
REVISION NOTES
EVOLUTION
Evolutionary Biology is the study of history of life forms
on the earth. To understand the changes in flora and
fauna that have occurred millions of years on earth we
must have a strong understanding of the context of life,
that is evolution of earth, the stars, and the universe
itself.
Origin of Life
The genesis of life is regarded as a one-of-a-kind occurrence
in the history of the cosmos. The universe is made up of a
massive cluster of galaxies. Galaxies include stars as well as
dust and smoke clouds.
The Big Bang Theory seeks to explain the origins of the
cosmos. According to this idea, a massive explosion occurs,
resulting in the formation of many galaxies.
Earth is thought to have originated some 4.5 billion years
ago in the Milky Way galaxy's solar system. The early Earth
had no atmosphere. The earth's surface was coated with
water vapour, methane, carbon dioxide, and ammonia
emitted by the molten mass.
The sun's UV rays split water into hydrogen and oxygen.
Life arose 500 million years after the Earth's formation.
Theories in support of Origin of Life
• Greek thinkers believed that spores brought from
other planets were the basic unit of life.
• According to another hypothesis, life emerges from
dead and decaying substances such as straw and dirt.
This is known as the hypothesis of spontaneous
origin.
• Louis Pasture demonstrated experimentally that life
can only come from pre-existing life. Following that, the
spontaneous theory of the origin of life is discarded.
• Oparin and Haldane argued that the initial form of life
may have evolved from non-living organic molecules
such as RNA and protein. Chemical evolution precedes
the origin of life. At that period, the earth's conditions
were as follows:
(i) high temperatures
(ii) volcanic eruptions, and
(iii) reducing atmosphere that comprised of CH4 and
NH3.
Miller’s Experiment: In 1953, S.L. Miller undertook an
experiment to demonstrate the origin of life on Earth in a
physical environment comparable to that which existed at the
time.
Miller created identical temperature and pressure conditions
in the laboratory. At 8,000 degrees Celsius, he established an
electric discharge in a flask containing CH4, H2, NH3, and water
vapour.
After 15 days of electric discharge, he saw the synthesis of
amino acids in a flask. Another scientist discovered the
creation of sugars, nitrogen bases, colours, and lipids in a
similar procedure.
Analysis of meteorite material revealed comparable
molecules, indicating that similar processes are taking place
elsewhere in space. This experimental evidence for the
genesis of life is referred to as the chemical evolution of life.
The first non-cellular forms of life may have evolved three
billion years ago. They might have been massive molecules
like RNA, Protein, and Polysaccharide, among others.
The cellular form of life most likely began as a single cell in an
aqueous medium. Biogenesis is the hypothesis that the initial form of life
evolved slowly through evolutionary processes from
non-living components.
Evidence of evolution:
some of the evidence of the
evolution of life forms are as follows:
(i) Paleontological evidence: Various ages of rock
sediments include remains of various living forms that
most likely died during the sediment's development.
Fossils are the hard remnants of life-forms discovered
in rocks. The study found that diverse forms changed
through time and that particular living forms had a
geological time span. As a result, new types of life have
emerged at various points throughout Earth's history.
(ii) Homologous organs: Homologous organs are ones that
perform distinct functions but have a similar origin and
structure. Humans, cheetahs, bats, and whales, for
example, show similarities in the arrangement of
bones in their forelimbs, despite the fact that these
forelimbs serve different tasks in these creatures.
Because of adaptation to distinct demands, these
animals evolved identical structures in opposite
orientations. This is referred to as divergent evolution.
(iii) Analogous structures: They are not morphologically
identical organs, yet they serve the same purpose. For
example, the eyes of mammals and octopuses, as
well as the flippers of penguins and dolphins. This is
because distinct groups of species have comparable
adaptation traits owing to similar environment. This process of evolution is known as convergent
evolution.
(iv) Biochemical evidence: Similarities in proteins and
genes that execute the same function in different species
suggest a common ancestor. These molecular
similarities, like structural similarities, indicate
common ancestor.
Evolution by Natural Selection
Industrial Melanism: Natural selection was seen in a
peppered moth in England in the 1850s, prior to
industrialization (Biston betularia).
• This moth came in two colours: grey and black
(Carbonaria). Before industrialisation in the early
nineteenth century, only the grey-colored moths were
present; the black ones were uncommon.
• The grey-colored moths were found on tree trunks
coated in lichens, allowing them to flee their assailants.
• Later, around 1920, when industries developed, postindustrialization, the lichens died and the tree trunks
became black owing to the deposition of industrial soot.
Birds may now locate these moths and feast on them.
• As a result, the grey-colored moths were devoured by
the birds, but the dark-colored moths fled.
• The coal is currently being replaced by industries, which
utilise oil and electricity. This has resulted in less soot
generation and, as a result, decreased soot deposition on
tree trunks.
• These tree trunks have now become grey once more. As
a result, the number of grey-colored moths has grown
once more.
Evolution by Anthropogenic Selection: e.g. resistance of
mosquitoes to pesticides.
DDT was a huge success when it was used to control
mosquitoes. The majority of the mosquitos were DDT
sensitive and were so eliminated. Few mosquitos in that
population acquired resistant to DDT and survived. They
grew and now the entire mosquito population developed
resistance to DDT. The same pattern has been found in bacteria that are
multidrug resistant as a result of excessive medication and
pharmaceutical usage.
Adaptive Radiation:
it refers to the process of evolution of
diverse species in a specific geographical region that begins
at a point and spreads to other parts of geography (habitat).
Darwin's finches are an excellent illustration of adaptive
radiation. Australian marsupials developed from a common
ancestor stock, yet all lived on Australian island continents.
Convergent evolution occurs when more than one
adaptive radiation appears to have occurred in a
geographically separated location (representing
distinct ecosystems), for example, Placental mammals
and Australian marsupials.
Biological Evolution:
Nature favours the fittest, and fitness
is determined by hereditary qualities. Some species have
evolved to thrive in hazardous environments. Fitness is the
final outcome of one's capacity to adapt to and be chosen by
nature.
According to Lamarck, evolution of living forms happened
but was driven by the use and misuse of organs. He used
giraffes as an illustration of how they evolved their necks by
harvesting leaves on lofty trees and had to adjust by
elongating their necks.
The two essential principles of Darwinian Theory of
Evolution are:
(i) branching descent and
(ii) natural selection.
Darwin's theory of natural selection was based on
following observation:
• Natural resources are scarce.
• Population growth
• Competition for scarce resources
• Survival for existence.
• Survival of the fittest
Mechanisms of Evolution:
• Hugo deVries proposed the concept of mutation based on
his research on evening primrose (Oenothera
lamarckiana).
• A mutation is a substantial change that appears abruptly
in a population.
• Darwin variations are modest and directed, whereas
mutations are random and directionless.
• Hugo deVries thought that mutation produced
speciation, which he referred to as saltation (single step
large mutation).
Hardy-Weinberg Principle
The frequency of occurrence of alleles or genes in a given
population can be determined. These frequencies remain
constant and even during generation. Hardy-Weinberg
concepts were used to describe this information using an
algebraic equation.
According to this theory, allele frequencies in a population
remain steady and consistent from generation to generation.
The gene pool does not change. This is known as genetic
equilibrium, and the sum of all allelic frequencies equals 1.
Binomial expansion of (p + q)2= p2+2pq+q2=1 where p
and q are the frequencies of allele A and a in a population.
The frequency of AA people in a population is simply p2.
Just put, the likelihood of an allele A with a frequency of p
appearing on both chromosomes of a diploid person is simply
the product of the probabilities, i.e., p2. Similarly, aa is q2, and
Aa 2pq. As a result, p2 + 2pq + q2 = 1.
When measuring frequency, the actual value varies,
indicating the level of evolutionary changes.
Change of frequency in alleles (Hardy-Weinberg
equilibrium) in a population resulted due to evolution.
Factors Affecting Hardy-Weinberg principle are:
(i) Gene migration/gene flow
(ii) Genetic drift
(iii) Mutation
(iv) Genetic recombination
(v) Natural selection
During genetic drift, changes in allele frequency might be so
diverse in a population sample that they form a separate
species. The original drifted population becomes founder and
that effect is called founder effect.
Brief Account of Evolution
• The earliest cellular form of life evolved on
Earth some 2000 million years ago.
• Slowly, single-celled animals evolved into
multicellular forms, and by 500 million
years ago, invertebrates were developed
and active.
• Around 350 million years ago (mya), jawless
fish originated.
• Organisms began to spread from the sea to
the land. Fish with large and powerful fins
may travel on land and return to the water.
These lobefin creatures developed into the
earliest amphibians.
• These amphibians later evolved into
reptiles. They produce shelled eggs. The
planet was once dominated by reptiles of all
forms and sizes, including fish-like reptiles
such as Ichthyosaurs and terrestrial reptiles
such as dinosaurs. Tyrannosaurus rex was
the largest.
• Some of the reptiles developed into birds,
while others into mammals. Mammals were
viviparous and better at perceiving and
avoiding danger.
Origin and Evolution of Man
Dryopithecus: evolved in 15 mya. They were hairy and
walked like gorillas and chimpanzees. They were more apelike.
Ramapithecus: they were more man like.
Australopithecus: they lived in East African grasslands.
Discovered 2 mya. They hunted with stone weapons and ate
fruits.
Homo habilis: this was first human like. Its brain capacity
was 650-800cc. They did not eat meat.
Homo erectus: discovered 1.5 mya. They had a large brain
with a brain capacity of 900cc.
They ate meat.
Neanderthal man: it had a brain capacity of 1400cc and lived
near east and central Asia.
They used hides to protect their body and were the first to
bury their dead.
Homo sapiens: they arose in Africa and moved to other
continents and developed into different races.
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12th CLASS NOTES