Explain how natural selection leads to evolution, including the roles of variation, heritability, differential reproduction, and environment.

Explain how natural selection leads to evolution, including the roles of variation, heritability, differential reproduction, and environment.

• A. Variation is random and never inherited; evolution is driven by chance alone.
• B. Variation exists, is heritable, differential reproduction occurs, and environment drives allele frequencies over generations.
• C. All individuals have identical traits; evolution occurs only due to luck.
• D. Evolution requires no heritable variation.

Answer: (B)

The main idea is that evolution happens when differences among individuals that can be inherited affect who leaves offspring. Variation provides the raw material—different genetic differences among individuals. If those differences are heritable, offspring tend to resemble their parents for the traits in question. In any environment, some variants give individuals a higher chance of surviving and reproducing; those advantageous traits become more common in the next generation, so the population’s genetic makeup shifts over time. Repeating this across many generations, the environment continually shapes which traits are favored, leading to adaptation and evolution. Why this fits best: it integrates all four elements—variation, heritability, differential reproduction, and environment. Variation without inheritance wouldn’t accumulate changes across generations. Without differential reproduction, advantageous traits wouldn’t increase in frequency. Without the environment shaping which traits are advantageous, there’d be no consistent direction to change. And without heritable variation, selection wouldn’t produce lasting evolutionary change. Other options are inconsistent with how evolution works. One claims variation isn’t inherited and that evolution is driven by chance alone, ignoring how heredity and fitness differences guide changes over generations. Another says all individuals are identical, which eliminates the very variation selection acts on. The last claims evolution doesn’t need heritable variation, which contradicts the mechanism by which populations adapt over time.

The main idea is that evolution happens when differences among individuals that can be inherited affect who leaves offspring. Variation provides the raw material—different genetic differences among individuals. If those differences are heritable, offspring tend to resemble their parents for the traits in question. In any environment, some variants give individuals a higher chance of surviving and reproducing; those advantageous traits become more common in the next generation, so the population’s genetic makeup shifts over time. Repeating this across many generations, the environment continually shapes which traits are favored, leading to adaptation and evolution.

Why this fits best: it integrates all four elements—variation, heritability, differential reproduction, and environment. Variation without inheritance wouldn’t accumulate changes across generations. Without differential reproduction, advantageous traits wouldn’t increase in frequency. Without the environment shaping which traits are advantageous, there’d be no consistent direction to change. And without heritable variation, selection wouldn’t produce lasting evolutionary change.

Other options are inconsistent with how evolution works. One claims variation isn’t inherited and that evolution is driven by chance alone, ignoring how heredity and fitness differences guide changes over generations. Another says all individuals are identical, which eliminates the very variation selection acts on. The last claims evolution doesn’t need heritable variation, which contradicts the mechanism by which populations adapt over time.