Which of the listed examples is a current hypothesis regarding the Cambrian explosion?

• A. An increase in atmospheric CO₂ led to an explosion of plants and life-forms that fed on plants.
• B. Increased numbers of predator species led to a dramatic decline in prey species.
• C. A rise in atmospheric nitrogen led to success of large animals with higher metabolic rates.
• D. All of the listed responses are correct.
• E. Evolution of the Hox gene complex provided developmental flexibility.

Answer: (E)

Verified step by step guidance

1. Understand the Cambrian explosion: The Cambrian explosion refers to a period approximately 541 million years ago when there was a rapid diversification of life forms on Earth, particularly the emergence of most major animal phyla.
2. Identify the role of the Hox gene complex: The Hox gene complex is a group of related genes that control the body plan of an embryo along the head-tail axis. These genes are crucial for determining the identity and arrangement of body segments.
3. Evaluate the hypothesis: The hypothesis that the evolution of the Hox gene complex provided developmental flexibility suggests that changes in these genes allowed for more complex body structures and diversity in organisms, contributing to the rapid diversification seen during the Cambrian explosion.
4. Compare with other hypotheses: The other options provided (increase in atmospheric CO2, increased predator species, rise in atmospheric nitrogen) do not directly relate to the genetic and developmental changes that could lead to the diversity of body plans seen in the Cambrian period.
5. Conclude the reasoning: The hypothesis regarding the evolution of the Hox gene complex is considered a current and plausible explanation for the Cambrian explosion because it directly addresses the genetic mechanisms that could lead to increased complexity and diversity in animal forms.