2(a) Explain the concepts of Genetic Drift and Founder Effect with suitable anthropological examples.

Introduction

Genetic drift is a random change in allele frequencies in small populations due to chance events rather than natural selection. Introduced by Sewall Wright (1931), it explains evolutionary changes that occur without adaptive value. One of its important offshoots is the Founder Effect, which occurs when a new population is established by a small number of individuals, leading to reduced genetic variation and sometimes unique genetic characteristics.

Body

1. Genetic Drift

• Origin and Theory – Coined by Sewall Wright (1931), genetic drift describes random fluctuations in allele frequencies across generations, particularly in small or isolated populations.
• Mechanism – Alleles may increase or decrease in frequency purely by chance; once an allele is lost, it cannot reappear unless by mutation.
• Anthropological Example – The Tristan da Cunha islanders, settled by a few families in the early 19th century, exhibited a high frequency of retinitis pigmentosa due to genetic drift acting in a small, isolated population.

2. Founder Effect

• Definition – Proposed by Ernst Mayr (1942), the Founder Effect occurs when a small subset of a larger population establishes a new colony, carrying only a fraction of the genetic variation from the original population.
• Consequences – Reduced genetic diversity, fixation of certain alleles, and sometimes emergence of rare genetic disorders.
• Anthropological Examples –
  • Amish Community (USA): High incidence of Ellis–van Creveld syndrome (short-limbed dwarfism and polydactyly) due to limited founders.
  • Finnish Isolates: The Finnish population demonstrates several rare recessive disorders (“Finnish Disease Heritage”) arising due to founder effects and isolation.
  • Andaman Islanders: Genetic studies show low diversity and drift effects due to long-term isolation and small population size.

3. Interaction with Natural Selection

• While natural selection is directional and adaptive, genetic drift is random and non-adaptive.
• In small populations, drift may override selection by fixing or eliminating alleles irrespective of their adaptive value.
• Wright’s shifting balance theory emphasized the interplay between drift and selection in evolutionary change.

Contemporary Studies

“Genetic drift reminds us that evolution is not always purposeful — sometimes it is the story of chance, not choice.”

Conclusion

Genetic drift and founder effect demonstrate that evolutionary change is not solely driven by natural selection. Their influence is most visible in small, isolated populations — shaping genetic diversity, disease patterns, and anthropological variation. These concepts form a key bridge between genetics and population anthropology, deepening our understanding of microevolutionary processes.