Evolution Requires Genetic Changes
Definition
Evolution
Evolution is defined as a change in the heritable characteristics of a population over time.
Only traits that are genetically inherited (passed from parent to offspring via DNA) contribute to evolution.
Heritable vs. Acquired Characteristics
- Heritable traits: encoded in DNA, subject to mutation, recombination, and natural selection.
- Acquired traits: result from environmental influence or learning during an organism’s lifetime.
- Heritable traits: darker fur color in moths due to a genetic mutation.
- Acquired traits: a tennis player develops stronger bones and muscles in their dominant arm.
Acquired traits cannot be passed to offspring.
Darwinian Evolution (Natural Selection)
Definition
Natural selection
Natural selection is the process where individuals with traits better suited to their environment have higher reproductive success, passing these traits to the next generation.
Charles Darwin’s theory of evolution by natural selection explains how populations change:
- Variation exists in populations due to random mutations, crossing over, independent assortment, and random fertilization.
- Overproduction of offspring means competition for resources (food, space, mates).
- Selection pressures (predation, disease, climate, competition) affect survival chances.
- Individuals with advantageous heritable traits survive and reproduce more successfully.
- These traits (alleles) become more common in the population over time.
Lamarckism and Its Falsification
- Jean-Baptiste Lamarck proposed that acquired characteristics (traits gained during an organism’s lifetime) could be inherited.
- No mechanism exists for changes in muscle use, behavior, or environment-driven traits to alter DNA in gametes.
Giraffes stretched their necks to reach higher leaves, and this lengthened neck was passed to offspring.
NoteModern genetics, which was unavailable during Darwin’s time, has confirmed that evolution occurs through changes in DNA within populations, not through the inheritance of acquired traits.
TipIf asked to compare Darwin and Lamarck, always emphasize inheritance of heritable vs. acquired traits.
