Evidence for Evolution

Fossils

Fossils are the remains of ancient organisms that are found in rocks. They show what organisms looked like millions of years ago and can be used to work out how much they have changed and evolved. 

Fossils can be formed in 3 different ways:

1. Parts of organisms that will not decay easily, like bones, shells and teeth, eventually get replaced by minerals. The minerals will form rocks with the same original shape. The surrounding sediments also turn to rock but the fossil will still be distinct from the rest of the rock.
2. Soft material like clay can harden around whole organisms, traces of organisms (e.g. footprints), burrows or rootlet traces, forming a cast. 
3. When certain conditions are lacking, decay cannot happen and organisms are preserved. Examples include ice, peatbogs, amber and tar pits.

Fossils found deeper in the soil are generally from more simple organisms. This supports Darwin’s theory of evolution that all organisms evolved from these simple life forms. 

However, the fossil record is incomplete. This is because many early forms of life were soft-bodied so left very few traces behind and many of the fossils that were made have been destroyed by geological activity.

Evolutionary Trees

Antibiotic Resistance in Bacteria

Bacteria reproduce very quickly in a process called by binary fission. This means that they evolve rapidly.

Mutations often occur in the DNA of bacterial pathogens. Some of these mutations lead to changes in characteristics of the bacteria and may even cause the bacteria to become resistant to certain antibiotics. Due to their high rate of reproduction, entire antibiotic-resistant strains can evolve very quickly.

Antibiotic resistance is very beneficial to the bacterial pathogen as it will not be killed by antibiotics, can reproduce a lot more and the population can grow. However, for humans or other hosts, antibiotic resistance cause big problems because the antibiotics that are used to treat people with bacterial infections will no longer work. This means infected people continue being ill and spread the disease to more people.

Scientists try to develop new antibiotics that bacterial strains are not resistant to but the process is expensive and slow. Also, some ‘superbugs‘ are resistant to all known antibiotics. MRSA is a ‘superbug‘ that usually affects vulnerable people in hospitals and can be fatal. 

Preventing the evolution of antibiotic resistance:

• Overuse of antibiotics has caused antibiotic resistance to develop rapidly so doctors should avoid inappropriate prescribing of antibiotics e.g. in non-serious infections or viral infections.
• To make sure antibiotics definitely kill the bacterial pathogens so they do not mutate and develop resistance, patients must complete the full course of antibiotics. 
• Antibiotics are often used in farming, to prevent illness and increase growth rate. Bacteria in the animals can also can develop resistance to the antibiotics if overused and these resistant strains can be passed to humans when meat is consumed. Using less antibiotics in farming will help to reduce the amount of antibiotic resistant bacterial strains.