Charles Darwin developed the theory of evolution by natural selection after observing that species evolve over generations through natural processes. His theory proposed that species share common ancestors and that traits within a population become more or less common through natural selection as organisms with beneficial traits are more likely to survive and reproduce. The theory can explain how antibiotic resistance has developed in bacteria, as bacteria with genetic mutations that allow survival despite antibiotics will pass on those resistance traits.

2. ESSENTIAL IDEA :
The diversity of life has evolved and continues to
evolve by natural selection
NATURE OF SCIENCE :
Use theories to explain natural phenomena – the
theory of evolution by natural selection can explain the
development of antibiotic resistance in bacteria

3. THEORY OF NATURAL SELECTION
•Charles Darwin, a biologist from England, set off
on the ship HMS Beagle to investigate species of
the island, in the 19th century.
•He soon developed a theory that would contradict
the creation of man
•He imply that all species derived from common
ancestors through process called natural selection

4. NATURAL SELECTION
The gradual process by which biological traits become
either MORE or LESS common in a population,
make them better adjusted to an environment, tend to
survive, reproduce and increase in number,
therefore, are able to TRANSMIT their essential
genotypic qualities to succeeding generations.

5. • The term was popularized by Charles Darwin who intended it
to be compared with artificial selection, now more commonly
referred to as selective breeding.
• Darwin accumulate facts to support the theory of evolution by
natural selection.
• Can only occur if one species varies.
• Mutation, meiosis and sexual reproduction cause variation
between individuals in a species.
• Natural selection is a key mechanism of evolution.
NATURAL SELECTION

6. • Darwin's Theory of Evolution is the widely held notion that all
life is related and has descended from a common ancestor: the
birds and the bananas, the fishes and the flowers -- all related
• Darwin's general theory presumes the development of life
from non-life and stresses a purely naturalistic (undirected)
"descent with modification". That is, complex creatures evolve
from more simplistic ancestors naturally over time
• As random genetic mutations occur within an organism's
genetic code, the beneficial mutations are preserved because
they aid survival -- a process known as "natural selection."
THEORY OF NATURAL SELECTION

7. • These beneficial mutations are passed on to the next
generation. Over time, beneficial mutations accumulate and
the result is an entirely different organism (not just a variation
of the original, but an entirely different creature).
• Natural selection acts to preserve and accumulate minor
advantageous genetic mutations. Suppose a member of a
species developed a functional advantage (it grew wings and
learned to fly). Its offspring would inherit that advantage and
pass it on to their offspring. The inferior (disadvantaged)
members of the same species would gradually die out, leaving
only the superior (advantaged) members of the species.

8. Darwin’s five theories were:
i. Evolution: Species come and leave through time, while they exist they
change.
ii. Common descent: Organisms are descended from one, or several common
ancestors and have diversified from this original stock
iii. Species multiply: The diversification of life involves populations of one
species diverging until they become two separate species; this has probably
occurred billions of times on earth!
iv. Gradualism: Evolutionary change occurs through incremental small
changes within populations; new species are not created suddenly.
v. Natural selection: Evolutionary change occurs through variation between
individuals; some variants give the individual an extra survival probability.

10. • Darwin observed in the natural world around him. He saw that
organisms produce more offspring than is required to replace
themselves, so population sizes should increase rapidly (think
about the number of frogspawn laid each year, or how many
eggs a spider lays). Fact #1 ; ‘super fecundity’(fertile)
• However Darwin saw for himself, and confirmed his
observation with others, that population numbers tend to stay
at about the same level (you don’t see a doubling of the
number of frogs or mice in your garden each year do you?):
that’s fact #2 ; ‘Steady population’

11. • Darwin found the answer with another fact: resources, such as
food, water or places to sleep or mate, are limited. Human
population was increasing at a rapid pace and would soon run
out of food, water and space. Fact #3 ; ‘Limited resources’
• Organisms who die as the consequences of this competition
were not totally random, Darwin found that those organisms
more suited to their environment were more likely to survive.
• ‘Survival of the fittest’ - organisms most suited to the
environment had more chance of survival.

12. • Next, Darwin made two other observations about individuals.
First he had come to the conclusion through his work on the
H.M.S. Beagle, when he was working on barnacles and later
pigeons, that individuals are unique and that individuals vary in
almost every aspect: that’s fact #4, ‘Individuals are unique’
• Fact #5 ; ‘Heritability of differences’. Darwin had taken to breeding
pigeons to investigate variability further. He performed many
crosses between different breeds of fancy pigeons to look at
whether their offspring had the same variations. He also collected
lots of observations from various animal and plant breeders to
help him draw out the conclusion that these individual differences
are heritable: they are passed on from parent to offspring.

13. • As the consequences, a changing environment would mean
different characteristics would be favourable in a changing
environment. Darwin believed that organisms had evolved to
suit their environments and occupy an ecological niche, where
they would be best suited to their environment.
• As the above indicates, those alleles of a species that are
favoured in the environment will become more frequent in the
genomes of the species, due to the organisms higher likeness
of surviving as part of the large species.

16. • Antibiotic resistance is a consequence of evolution via natural
selection.
• The antibiotic action give pressure; those bacteria which have
a mutation allowing them to survive will live on to reproduce.
• They will then pass this trait to their offspring, which will be a
fully resistant generation.
• Some bacteria have developed resistance to antibiotics that
were once commonly used to treat them
ANTIBIOTIC RESISTANCE IN BACTERIA