Question

Which of the following was probably the least important factor

in bringing about the Cambrian explosion?

(A) the emergence of predator-prey relationships

(B) an increase in the concentration of atmospheric oxygen

(C) the movement of animals onto land

(D) the origin of Hox genes

Short answer

(A) The option “the emergence of predator-prey relationships” is false.

(B) The option “an increase in the concentration of atmospheric oxygen” is false.

(C) The option “the movement of animals onto land” is true.

(D) The option “the origin of Hox genes” is false.

Step-by-step solution

Evolution of animals

The animals are eukaryotes that first originated in the Neoproterozoic era. These animals had small body structures without any skeletal tissues; that is, the initial animals were soft-bodied (termed). The change in environmental conditions and the passage of time led to the slow evolution of animals.

Explanation of option ‘(A)’

In the Cambrian age, prey animals developed protective measures such as an exoskeleton, and the predator animals evolved to locomote; these changes resulted in a new pattern of prey-predator relationship. The new relationship was favored by nature and led to the decline of Ediacaran fauna.

Thus, this statement contains an important factor related to the Cambrian explosion.

Therefore, the given option is false.

Explanation of option ‘(B)’

The atmospheric content of oxygen before the Cambrian period was relatively low, and the elevation in oxygen levels favored the diversification of animals and the emergence of organisms with greater body size and a higher rate of metabolism.

Thus, the Cambrian explosion was favored by increased levels of atmospheric oxygen.

Therefore, the given option is false.

Explanation of option ‘(C)’

The animals too evolved in marine habitat and slowly evolved to colonize land habitat. This modification was first observed by the emergence of arthropods in the Cambrian age, but it did not increase or decrease the diversity of animals. The explosion of animals occurred a little after land colonization.

Thus, the movement of animals onto and did not affect the Cambrian explosion to a large extent.

Therefore, the given option is true.

Explanation of option ‘(D)’

The structural as well as the physiological aspect of every organism, is influenced by genomic content. The emergence of Hox genes in the genome of new organisms favored diversification and resulted in the development of various animal groups.

Thus, Hox genes do influence the Cambrian explosion.

Therefore, the given option is false.