Natural selection is a phenomenon wherein nature, in the wild ,selects traits favourable to the species in its environment.
genetic drift is a random change in the frequency of certain genes in a population over generation or the random changes in the gene frequency occuring by chance alone.
geographical isolation means change in topography and it doesn't play any role in the speciation of asexually reproducing animals and self pollinating plants.

**Natural Selection:**

Natural selection is a fundamental concept in biology that refers to the process by which certain traits or characteristics become more or less common in a population over time. It is driven by the interaction between genetic variation within a population and the environment in which the population exists.

**Mechanism of Natural Selection:**

The mechanism of natural selection involves several key components:

1. **Variation:** Within a population, individuals possess genetic variations that result in different traits or characteristics. These variations can be inherited from their parents or arise from genetic mutations.

2. **Selection Pressure:** The environment exerts selective pressures on the individuals within a population. These pressures can include factors such as predation, competition for resources, or changes in climate.

3. **Differential Reproduction:** Individuals with advantageous traits have a higher likelihood of survival and reproduction compared to individuals with less favorable traits. As a result, the genes associated with advantageous traits become more common in the population over successive generations.

4. **Inheritance:** The advantageous traits are passed down to offspring through genetic inheritance, and the process of natural selection continues.

**Genetic Drift:**

Genetic drift refers to the random fluctuation of allele frequencies in a population over time. Unlike natural selection, which is driven by selective pressures, genetic drift is a result of chance events.

**Factors Contributing to Genetic Drift:**

1. **Population Size:** Genetic drift is more pronounced in smaller populations, as chance events have a greater impact on allele frequencies.

2. **Founder Effect:** When a small group of individuals migrates or becomes isolated from the larger population, the resulting population may have limited genetic diversity due to the alleles present in the founding individuals.

3. **Bottleneck Effect:** Following a significant reduction in population size, genetic diversity decreases due to the loss of alleles. The surviving population may exhibit different allele frequencies compared to the original population.

**Geographical Isolation:**

Geographical isolation is a type of reproductive isolation that occurs when physical barriers, such as mountains, rivers, or oceans, separate populations of a species. This isolation prevents gene flow between the separated populations.

**Effects of Geographical Isolation:**

1. **Genetic Divergence:** Geographical isolation can lead to genetic divergence between separated populations. Over time, the populations may accumulate genetic differences, which can result in the formation of new species.

2. **Inbreeding:** Geographical isolation limits the pool of potential mates, increasing the likelihood of individuals within a population breeding with close relatives. This can lead to inbreeding depression, which reduces the fitness and overall health of the population.

3. **Adaptive Radiation:** Geographical isolation can also promote adaptive radiation, where populations in different environments face distinct selective pressures. This can lead to the evolution of diverse adaptations and the emergence of multiple new species.

In summary, natural selection is the process by which advantageous traits become more common in a population over time, driven by selective pressures. Genetic drift, on the other hand, refers to random fluctuations in allele frequencies due to chance events. Geographical isolation occurs when physical barriers separate populations, leading to genetic divergence and potential speciation.