Final answer:
The major downside of artificial selection in crops like broccoli and cabbage from the wild mustard plant is decreased genetic diversity, leading to potential vulnerabilities. While artificial selection is driven by human choices and differs from natural selection, it still provides evidence for evolution by selection pressures.
Step-by-step explanation:
The primary consequence of artificial selection such as that which created crops like broccoli, cauliflower, kale, and cabbage from the wild mustard plant, is decreased genetic diversity. This decrease in diversity can lead to increased vulnerability to diseases and pests because the crops become more genetically uniform. Although artificial selection can lead to attributes like enhanced growth rate or improved nutritional value, it sometimes comes at the cost of reduced genetic variance within the species. This mirrors the issues faced during the Irish potato famine where lack of crop diversity resulted in massive crop failure and widespread famine. Additionally, artificial selection can potentially decrease the pool of genetic traits that could be valuable for future adaptations and survival.
Artificial selection is similar to Darwin's conception of natural selection in that both processes result in changes in the traits of populations over time. However, while natural selection is driven by survival advantages within a given environment, artificial selection is driven by human preferences. Despite this difference, artificial selection can serve as evidence for evolution by natural selection by illustrating how selection pressures (in this case, human-induced) can lead to significant changes in organisms over generations. This demonstrates the adaptability and plasticity of genetic traits within populations.