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

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

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.

• 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

• 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

• 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.

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.

• 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’

• 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.

• 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.

• 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.

• 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