Final answer:
Genetic variation in natural populations was traditionally measured by genetic drift, the Hardy-Weinberg principle, and geographical variation. These concepts help understand the genetic structure and distribution of genotypes, indicating how populations may adapt to their environments.
Step-by-step explanation:
The early views on genetic variation in natural populations largely revolved around the extent of genetic diversity and the processes influencing it, such as genetic drift, natural selection, and geographical isolation. The Hardy-Weinberg principle provides a mathematical baseline for comparing non-evolving and evolving populations to determine which evolutionary forces might be at play if there are deviations from expected allele frequencies.
For example, considering two separated populations of flowers with different counts of blue and red flowers, the changes in allele frequencies might indicate the effect of genetic drift or natural selection. Population 1, with a significant decrease in red flowers compared to blue, could imply genetic drift due to its small population size affecting the genetic structure. In contrast, Population 2 might suggest natural selection if the proportion of red flowers has remained substantial despite the large population size. Additionally, geographical variation, defined as differences in phenotypic variation between geographically separated populations, plays a critical role in this diversification process. The concepts of genetic variance, the gene pool, and population carry, highlight the importance of allele and genotype distribution across different environments which could lead to adaptations within populations.