4.6.3 The development of understanding of genetics and evolution

4.6.3.1 Theory of evolution (biology only)

Theories of Evolution

• Theories of evolution have been bandied around from around the 18th century.
  • Before this period of time, the general understanding was that creationism led to all of the organisms around us.
  • In the 1700s, theories began to form.
  • The current theory that we follow is that of Charles Darwin.

Darwin’s Theory of Evolution

• Darwin journeyed to the Galapagos Islands and spent long periods of time observing life on these islands.
• He proposed the theory of natural selection.

Natural Selection

• Individual organisms in a certain species show more variation for a certain characteristic.
  • Some organisms in a species may have more variation than others for a certain characteristic, for example some giraffes may have longer necks than others

• Individuals with characteristics most suited to the environment are more likely to survive to breed successfully.
  • They will survive for longer such as if a lion is stronger, it will survive for longer and so will be able to breed more.

• The characteristics that have enabled these individuals to survive are then passed onto the next generation.
  • As the parents have a genetic advantage, they will pass this onto their offspring.
  • This will allow them also to survive for longer to reproduce. These organisms are the ‘fittest.’

Reaction to Darwin’s Theories

• Darwin received a frosty reception to his critical work ‘On the Origin of Species, released in 1859.
• He upset many creationists, who believed that the theory challenged their notion that God created all of the plants and animals that raised on Earth.

Reaction to Darwin’s Theories

• There were other factors that initially caused Darwin problems.
  • Understanding of genes was still in its infancy.
• The lack of evidence was Darwin’s greatest problem.
  • It meant that Darwin could never truly gain the recognition he deserved for his theory  in his lifetime.

Lamarck’s Theory of Evolution

• Lamarck’s theory was known as the inheritance of acquired characteristics.
  • Inheritance of acquired characteristics stated that if the parents had changes in their lifetime, they would be passed on to the offspring.

4.6.3.2 Speciation (biology only)

Competitive Scientists

• Darwin was in competition with another scientist called Alfred Wallace.
  • He independently published his own theories regarding natural selection and evolution.
  • However, he is most famed for his ideas on speciation.

Competitive Scientists

• Wallace proposed a theory of natural selection at the same time as Darwin.
• Theory of Speciation: Natural selection can lead to formation of a new species if there is a split in the population.
• For example, geographical isolation could separate two populations of monkeys over two islands.

1-1 GCSE Biology Tutoring

Boost your Biology exam scores with personalised lesson plans, tailored to your needs

Book a FREE Consultation

4.6.3.3 The understanding of genetics (biology only)

Genetics Basis

• Mendelian genetics forms the basis of our understanding of genetics.
  • He carried out experiments breeding plants in the mid 19th century.
  • He worked out the understanding of dominance in plants and monohybrid inheritance.

Genetics Basis

• Certain characteristics are controlled by only one gene.
  • These characteristics are affected by monohybrid inheritance.

Genetics Basis

• To investigate this, he looked at the difference between smooth and wrinkled peas to work out which were dominant and recessive characteristics.
• Over time, experiments worked out that Mendel’s units were in fact linked to chromosomes and they were actually the first understanding of what genes were.

4.6.3.4 Evidence for evolution

Evolution Evidence

• The general understanding is that fossils and antibiotic resistance can be used to prove evolution.
• Now, although creationist beliefs are still prevalent, the most commonly believed doctrine is that of Darwin’s Theory of Evolution by Natural Selection.

Evolution Evidence

• The way that genes are passed onto offspring, with similar characteristics seen between generations of organisms is proof of natural selection.
• Usually the characteristics that provide a survival advantage are passed on.

4.6.3.5 Fossils

Creation of Fossils

• Fossils are a product of the preservation of the remains of dead organisms over the course of millions of years.
• Certain parts of organisms do not decay.
  • Through weathering, these remains then can turn to rock.

Creation of Fossils

• In order for decay to occur, certain temperatures, oxygen content and water are needed.
• Some environmental conditions can lead to decay, for example when animals are stored in peat, ice, tar and amber, they can become trapped away from the required oxygen, water and temperatures.

Fossils as Evidence

• As seen in Darwin’s theory of evolution, simple life forms developed into more complex ones.
• Some of the oldest life forms had soft body forms.
  • This means that there was very little else left behind over time.
  • Geological activity, such as tectonic plate movement and earthquakes have destroyed the majority these fossils.

Fossils as Evidence

• By watching the developments of fossils over time and comparing and contrasting their ages, scientists can track the development of life over time.
  • This is difficult and involves conjecture, however can be used to get a brief understanding of development, pending further research.

Evolutionary Trees

• The two trees above can be used to map evolutionary relationships between organisms.
• In the second graph, all of the organisms have the same common ancestor.
  • Each branch represents speciation.
  • As all of the organisms come from the same first branch, they show that they are all from the same ancestor.

GCSE Biology Online Course

Covering every topic in the GCSE syllabus

Buy Now£29

4.6.3.6 Extinction

Extinction

• Extinction occurs when all of the members of a species die.
  • This occurs with dinosaurs, after the catastrophic event of the asteroid.
  • It occurs when individuals are no longer adapted to the surroundings.
• This happens when there are new predators, diseases or more successful, better adapted competitors, thus removing their food source.
  • A catastrophic event, along with changes to the environment over time can lead to extinction.

• Extinction has happened to many organisms.
  • The woolly mammoth, dodo, passenger pigeon and quagga are just a few examples of organisms that have become extinct.

4.6.3.7 Resistant bacteria

Bacterial Reproduction

• Bacteria have an incredible ability to reproduce at a truly quick rate.
  • This has allowed them to evolve rapidly, with whatever abilities were required.

• Mutations occur rapidly and randomly.
  • Sometimes when they occur, they provide bacteria with a selective advantage.
  • This advantage could be resistance to antibiotics.

Bacteria and Antibiotic Resistance

• Bacteria that are resistant to antibiotics will survive for longer than bacteria that is not resistant.
  • They will therefore reproduce more and then survive for longer, increasing the population of the resistant strain.

MRSA

• MRSA is an example of an antibiotic resistant strain of bacteria.
  • The abbreviation stands for Methicillin Resistant Staphylococcus aureus.
  • This means that the bacteria are resistant to the antibiotic Methicillin, which is one of the stronger varieties.
• There are many methods for reducing the rates of development of antibiotic resistant strains of bacteria.
• These include:
  • The correct prescription of antibiotics.
  • The course of antibiotics must be completed.
  • A reduction in the use of agricultural antibiotics.

Prescriptions

• Antibiotics must only be prescribed when necessary.
  • This means that they are not required in those with viral infections or non-serious infections.

Courses

• If the course of antibiotics is not completed, there is an increased risk that not all of the bacteria is eliminated.
• This can lead to more and more bacteria being present that can mutate and become resistant.

Agricultural Antibiotics

• Antibiotics are widely used in agriculture.
  • Vancomycin, for example, is used often to promote growth in cattle, pigs and chicken.
  • This use also can lead to an increase in antibiotic resistance as there is an increased chance of mutation occurring.

New Antibiotics

• With all of this in mind, you may wonder, why not begin to develop new antibiotics.
  • Pharmaceutical companies stand to gain very little money from providing this service.
  • Moreover, this research takes a lot of time and is superseded by the newer strains.