Which of the following is NOT an example of evolution?
(a) Beak size in a population of birds becomes larger from one generation to the next because larger beaked birds had higher reproductive success and passed the trait to their offspring
(b) Over long periods of time whales gradually lost their hindlimbs
(c) When traveling to high altitude, human physiology changes to accommodate lower oxygen levels
(d) All of the above are examples of evolution
The correct answer and explanation is :
The correct answer is (c) When traveling to high altitude, human physiology changes to accommodate lower oxygen levels.
Explanation:
Evolution refers to a genetic change in a population over generations. It involves heritable changes in traits due to mechanisms like natural selection, mutation, genetic drift, or gene flow. Crucially, evolution happens across generations and involves changes in the genetic makeup of a population — not just temporary changes in individuals.
Let’s break down each option:
- (a) describes an example of natural selection driving evolutionary change. Birds with larger beaks have a reproductive advantage, pass their genes to offspring, and over generations, the population’s average beak size increases. This is evolution by natural selection.
- (b) is a classic example of evolutionary change over millions of years. Fossil evidence shows that ancient whale ancestors had hindlimbs, but as they adapted to aquatic life, these limbs reduced and nearly disappeared — a gradual, genetic change across many generations.
- (c) refers to physiological acclimatization, not evolution. When an individual travels to a high-altitude environment (like the Himalayas or Andes), their body adapts by producing more red blood cells to cope with lower oxygen. However, these changes are temporary and not genetic; they do not get passed to offspring. Once the individual returns to sea level, their physiology can return to normal. Since evolution involves genetic change passed through reproduction, (c) is not an example of evolution.
- (d) is incorrect because not all the examples given (specifically (c)) are examples of evolution.
Thus, (c) is the best answer because it describes a short-term, non-heritable, individual adjustment, not a population-level genetic change over time.