**Directional Selection**

Directional selection is a type of natural selection that favors individuals with traits at one extreme of the phenotypic range. This means that individuals with extreme variations of a particular trait have a higher chance of survival and reproduction compared to individuals with average or intermediate traits. Over time, this leads to a shift in the average phenotype of the population towards the favored extreme.

**Example:**
- In a population of giraffes, if longer necks provide an advantage in reaching food sources (such as leaves on tall trees), individuals with longer necks will have a higher chance of survival and reproduction compared to individuals with shorter necks. This will lead to a gradual increase in the average neck length of the population over generations.

**Disruptive Selection**

Disruptive selection is a type of natural selection that favors individuals with extreme traits on both ends of the phenotypic range, while individuals with average or intermediate traits are selected against. This leads to the splitting of a population into two distinct groups with different phenotypes.

**Example:**
- In a population of birds, if large beaks are advantageous for cracking hard seeds, and small beaks are advantageous for feeding on soft fruits, individuals with either large or small beaks will have higher chances of survival and reproduction compared to individuals with intermediate-sized beaks. As a result, the population may split into two groups, with one group having large beaks and the other group having small beaks.

**Balancing Selection**

Balancing selection is a type of natural selection that maintains genetic diversity in a population by favoring individuals with different phenotypes. This occurs when multiple alleles for a gene are actively maintained in a population over time.

**Example:**
- In a population of humans, the sickle cell trait is an example of balancing selection. Individuals who are heterozygous for the sickle cell gene have an advantage in regions where malaria is prevalent. They are less likely to develop severe forms of malaria compared to individuals without the sickle cell gene or individuals with two copies of the sickle cell gene. As a result, the sickle cell trait is maintained in the population.

**Stabilizing Selection**

Stabilizing selection is a type of natural selection that favors individuals with intermediate traits, while individuals with extreme traits on either end of the phenotypic range are selected against. This leads to a reduction in genetic diversity and a narrowing of the phenotypic range.

**Example:**
- In a population of birds, if medium-sized beaks are advantageous for accessing a wider range of food sources, individuals with medium-sized beaks will have a higher chance of survival and reproduction compared to individuals with very small or very large beaks. This will result in a decrease in the frequency of individuals with extreme beak sizes and an increase in the frequency of individuals with intermediate beak sizes.