Back to B6 home
B6 I) Natural Selection
B6 I) Natural Selection
Darwin’s theory of evolution stated that all species of living things have evolved from simple life forms that first developed more than 3 billion years ago.
Natural Selection
Charles Darwin came up with a theory about evolution called evolution by natural selection. Darwin observed that there is a wide variety of different characteristics within a species (all of the different organisms within a species had slightly different phenotypes). He also observed that all of these individuals compete for limited resources like food, water, light for plants etc. He then concluded that organisms that had the best characteristics were more suited to obtain these limited resources, thus meaning that they are more likely to survive. As these organisms are more likely to survive, they are more likely to reproduce, which means that their characteristics will be passed onto future generations – this will result in these characteristics becoming more prevalent (common) in the species.
Any characteristic that isn’t favourable would mean that the individual would be less able to obtain these limited resources, thus meaning that they are less likely to survive (more likely to die). As this individual is more likely to die, they will not reproduce, which means that they will not pass their characteristics onto future generations. This will mean that these characteristics will become less prolific (common) in the species.
Giraffe Example
Let’s now suppose that there is a mutation that results in a giraffe having a slightly longer neck. The longer necked giraffe will be able to reach higher up leaves on trees, which means that it is able to get plenty of food. This increases the chances of survival for the giraffe, which means that it is more likely to reproduce and pass on these longer necked genes onto future generations. This will result in there being a greater number of giraffes with longer necks in the population.
The giraffes with shorter necks in the population will now have characteristics that are less favourable. This is because the shorter necked giraffes will be unable to reach as high in trees, which may mean that they won’t be able to get sufficient food for survival, which could result in the shorter necked giraffes dying. As the shorter necked giraffes die, they won’t reproduce and therefore won’t pass their genes onto future generations. This will result in giraffes with shorter necks becoming less prolific in the population.
Charles Darwin came up with a theory about evolution called evolution by natural selection. Darwin observed that there is a wide variety of different characteristics within a species (all of the different organisms within a species had slightly different phenotypes). He also observed that all of these individuals compete for limited resources like food, water, light for plants etc. He then concluded that organisms that had the best characteristics were more suited to obtain these limited resources, thus meaning that they are more likely to survive. As these organisms are more likely to survive, they are more likely to reproduce, which means that their characteristics will be passed onto future generations – this will result in these characteristics becoming more prevalent (common) in the species.
Any characteristic that isn’t favourable would mean that the individual would be less able to obtain these limited resources, thus meaning that they are less likely to survive (more likely to die). As this individual is more likely to die, they will not reproduce, which means that they will not pass their characteristics onto future generations. This will mean that these characteristics will become less prolific (common) in the species.
Giraffe Example
Let’s now suppose that there is a mutation that results in a giraffe having a slightly longer neck. The longer necked giraffe will be able to reach higher up leaves on trees, which means that it is able to get plenty of food. This increases the chances of survival for the giraffe, which means that it is more likely to reproduce and pass on these longer necked genes onto future generations. This will result in there being a greater number of giraffes with longer necks in the population.
The giraffes with shorter necks in the population will now have characteristics that are less favourable. This is because the shorter necked giraffes will be unable to reach as high in trees, which may mean that they won’t be able to get sufficient food for survival, which could result in the shorter necked giraffes dying. As the shorter necked giraffes die, they won’t reproduce and therefore won’t pass their genes onto future generations. This will result in giraffes with shorter necks becoming less prolific in the population.
Development Over Time
Darwin theory of natural selection was unable to explain why the differences in characteristics in organisms occurred and how they were passed onto future generations. This is because knowledge of genetics and mutations was not known when Darwin was coming up with his theories. Increases in scientific knowledge has meant that we can now explain why the differences in characteristics occur and how they are passed onto future generations.
Also, we have found lots of evidence that supports Darwin’s theory of evolution by natural selection. Some of the evidence for his theory is from fossils, which are preserved remains, impressions or traces of any once living organism. By looking at fossil records, we can see how organisms have developed/ changed over time.
Some more evidence for evolution by natural selection has come from bacteria that are now resistant to antibiotics. The bacteria became resistant to antibiotics because of a mutation (a change in an organism’s DNA/ genes). This mutation allows the bacteria to survive despite the presence of antibiotics. As the antibiotic resistant bacteria survives, it reproduces and passes the antibiotic resistant gene onto future generations, which results in more of the offspring being resistant to antibiotics – antibiotic resistance becomes more common in the population (the bacteria that are not resistant to the antibiotics will not survive, which means that they will not reproduce and therefore will not pass their genes onto future generations. This results in bacteria that are not resistant to antibiotics becoming less prolific in the population).
Darwin theory of natural selection was unable to explain why the differences in characteristics in organisms occurred and how they were passed onto future generations. This is because knowledge of genetics and mutations was not known when Darwin was coming up with his theories. Increases in scientific knowledge has meant that we can now explain why the differences in characteristics occur and how they are passed onto future generations.
Also, we have found lots of evidence that supports Darwin’s theory of evolution by natural selection. Some of the evidence for his theory is from fossils, which are preserved remains, impressions or traces of any once living organism. By looking at fossil records, we can see how organisms have developed/ changed over time.
Some more evidence for evolution by natural selection has come from bacteria that are now resistant to antibiotics. The bacteria became resistant to antibiotics because of a mutation (a change in an organism’s DNA/ genes). This mutation allows the bacteria to survive despite the presence of antibiotics. As the antibiotic resistant bacteria survives, it reproduces and passes the antibiotic resistant gene onto future generations, which results in more of the offspring being resistant to antibiotics – antibiotic resistance becomes more common in the population (the bacteria that are not resistant to the antibiotics will not survive, which means that they will not reproduce and therefore will not pass their genes onto future generations. This results in bacteria that are not resistant to antibiotics becoming less prolific in the population).
General Explanation for Evolution by Natural Selection
Here is the general explanation of evolution by natural selection. Mutations in the genetics of organisms leads to variation in the population. Any advantageous mutation means that the organism is more suited to their environment and are therefore more likely to survive. If they are more likely to survive, they are more likely to reproduce and pass these advantageous genes/ characteristics onto future generations – this will result in these characteristics becoming more prolific (common) in the species. Any disadvantageous mutation means that an organism is less suited to their environment and are therefore less likely to survive. If they are less likely to survive, they are less likely to reproduce and pass these disadvantageous genes/ characteristics onto future generations – this will result in these characteristics becoming less prolific (common) in the species.
Here is the general explanation of evolution by natural selection. Mutations in the genetics of organisms leads to variation in the population. Any advantageous mutation means that the organism is more suited to their environment and are therefore more likely to survive. If they are more likely to survive, they are more likely to reproduce and pass these advantageous genes/ characteristics onto future generations – this will result in these characteristics becoming more prolific (common) in the species. Any disadvantageous mutation means that an organism is less suited to their environment and are therefore less likely to survive. If they are less likely to survive, they are less likely to reproduce and pass these disadvantageous genes/ characteristics onto future generations – this will result in these characteristics becoming less prolific (common) in the species.
New Species
Over extremely long periods of time, the phenotype of organisms change so much due to natural selection that a new species is created. This process is known as speciation Different species are unable to reproduce with each other to produce fertile offspring. For example, a horse and a donkey cannot reproduce to produce fertile offspring (in this example, a horse and a donkey can produce offspring, but the offspring will not be fertile).
Over extremely long periods of time, the phenotype of organisms change so much due to natural selection that a new species is created. This process is known as speciation Different species are unable to reproduce with each other to produce fertile offspring. For example, a horse and a donkey cannot reproduce to produce fertile offspring (in this example, a horse and a donkey can produce offspring, but the offspring will not be fertile).
Extinction
Extinction is when a species does not exist anymore. The most famous example of an animal that is extinct is a dodo. There are 5 main different reasons for extinction, which are:
Extinction is when a species does not exist anymore. The most famous example of an animal that is extinct is a dodo. There are 5 main different reasons for extinction, which are:
- New diseases completely kill off a species
- New predators hunt the organisms and kill them
- New competitors that are better suited to the environment out compete the organisms for resources (food, space and water)
- The environment changes too quickly, which means that the organisms cannot survive in the new conditions (e.g. climate change)
- A single catastrophic event like a collision between an asteroid and the earth (made the dinosaurs extinct) or a large volcanic eruption (a large volcanic eruption would also affect the climate/ environmental conditions)