Q. 87 A population of Bees develops resistance to pesticides and the trait gets fixed within a few
generations. This is an example of
(A) macroevolution.
(B) disruptive selection.
(C) stabilizing selection.
(D) microevolution.
This SEO-optimized article breaks down a key biology question on bee populations developing pesticide resistance, highlighting the correct answer and detailing all options. Ideal for students studying evolution, genetics, and population biology.
Rapid evolution in action: A bee population gains pesticide resistance and fixes the trait in just a few generations. This scenario from biology exams tests your grasp of evolutionary concepts. Let’s dive into the correct answer and unpack every option with real-world ties to genetics and natural selection—perfect for students prepping for NEET, CSIR NET, or undergrad evolution courses.
The Correct Answer: (D) Microevolution
Bee populations developing pesticide resistance that becomes fixed quickly exemplifies microevolution. Microevolution refers to small-scale changes in allele frequencies within a population over short timescales, often observable within generations.
Here, a mutation conferring resistance spreads rapidly due to strong natural selection—pesticide-sensitive bees die, while resistant ones survive and reproduce. This shifts the population’s gene pool toward the resistance allele until it’s fixed (nearly 100% frequency). Classic lab and field studies, like those on Apis mellifera (honeybees), show this happening in 5-10 generations under pesticide pressure. It’s microevolution because it occurs within a species, not creating new ones.
Unlike broader changes, microevolution builds the foundation for larger patterns. In plant biology or microbiology contexts (e.g., antibiotic resistance in bacteria), this mirrors how populations adapt locally without speciating.
Option (A) Macroevolution: Big-Picture Evolutionary Shifts
Macroevolution involves large-scale patterns like speciation, mass extinctions, or major morphological changes over geological timescales (thousands to millions of years). Think Darwin’s finches diversifying into new species or the transition from fish to tetrapods.
Pesticide resistance in bees doesn’t qualify—it’s a single-trait adaptation within one population, not forming new species or altering bee taxonomy. No macro-scale divergence here; it’s confined to genetic tweaks in existing bees.
Option (B) Disruptive Selection: Favoring Extremes
Disruptive (or diversifying) selection pushes a population toward phenotypic extremes, reducing intermediates. For example, medium-sized beak sizes in finches might decline if small seeds favor tiny beaks and large seeds favor big ones, potentially splitting the population.
Bee resistance isn’t disruptive: Pesticide kills the susceptible “normal” phenotype, favoring one extreme (resistance). This creates a unimodal shift to resistance, not two peaks. If anything, it’s directional, not disruptive.
Option (C) Stabilizing Selection: Preserving the Average
Stabilizing selection favors average traits, weeding out extremes to maintain population stability. Human birth weight illustrates this—too small or too large reduces survival, so mid-range weights dominate.
In bees, pesticide resistance does the opposite: It eliminates the average (susceptible) bees, shifting the mean toward resistance. No stabilization; the trait frequency skyrockets, destabilizing the original population norm.
Why This Matters in Genetics and Research
This question underscores directional selection driving microevolution, a hotspot in population genetics. For researchers in Jaipur’s biotech hubs or Rajasthan’s agrotech scene, understanding this combats pesticide overuse in crops like mustard or cotton, where bee resistance threatens pollination. Tools like Hardy-Weinberg equations quantify it: If initial resistant allele p=0.01, selection can fix it fast via p′=p+spq/1−sq (where is selection coefficient).
Key takeaway: Microevolution like this fuels agriculture challenges and antibiotic crises—vital for molecular biology and ecology studies.
