Which statement correctly describes the role of chance in evolution? (4 points)
Mutations result in genetic variation for natural selection to occur.
Evolution by natural selection proceeds by an accumulation of changes that occur by chance.
New alleles by random changes can only occur through genetic drift.
An allele that increases evolutionary fitness cannot be lost from a population by chance occurrence.
The Correct Answer and Explanation is:
Correct Answer:
Evolution by natural selection proceeds by an accumulation of changes that occur by chance.
Explanation (300+ words):
The role of chance in evolution is a fundamental and fascinating concept in biology. While natural selection is often described as a non-random process that favors traits beneficial for survival and reproduction, the raw material upon which natural selection acts—genetic variation—arises primarily through random events.
The correct statement, “Evolution by natural selection proceeds by an accumulation of changes that occur by chance,” highlights that random mutations, genetic recombination, and random allele frequencies (due to processes like genetic drift) contribute to the genetic variation within populations. These random changes create diversity in traits, and this diversity is crucial for evolution to occur.
Let’s break this down:
- Mutations are changes in the DNA sequence. These can be caused by errors during DNA replication or by environmental factors. Importantly, mutations occur randomly—they are not directed toward an organism’s needs.
- Genetic recombination during meiosis (e.g., crossing over) is also a random process that shuffles genes and contributes to variation.
- Genetic drift refers to random changes in allele frequencies, especially in small populations. Even beneficial alleles can be lost, and harmful alleles can increase in frequency due to chance events.
Thus, while natural selection is not a random process—since it systematically favors traits that increase fitness—the input it depends on (mutations and variation) is random. Evolution is a combination of random (chance) and non-random (selection) processes.
Let’s also rule out the other options:
- “Mutations result in genetic variation for natural selection to occur.” — This is true, but it doesn’t directly describe the role of chance in evolution.
- “New alleles by random changes can only occur through genetic drift.” — This is incorrect; new alleles arise by mutation, not genetic drift.
- “An allele that increases evolutionary fitness cannot be lost from a population by chance occurrence.” — This is false; even beneficial alleles can be lost due to genetic drift, especially in small population?