Scientists have several hypotheses for why the Cambrian explosion occurred. Explain three of the hypotheses. What will be an ideal response?

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1. It is more likely that the Cambrian explosion was a combination of factors, both biologic
and geologic. For example, geologic evidence indicates that Earth was glaciated one or more
times during the Proterozoic, followed by global warming during the Cambrian. These global
environmental changes may have stimulated evolution and contributed to the Cambrian
explosion.
2. Others would argue that a change in the chemistry of the oceans favored the evolution of
mineralized skeletons. In this scenario, an increase in the concentration of calcium from the
Neoproterozoic through the Early Cambrian, in part due to volcanism along mid-oceanic
ridges, allowed for the precipitation of calcium carbonate and calcium phosphate, compounds
that make up the shells of most invertebrates
3. Another hypothesis is that the rapid evolution of a skeletonized fauna was a response to the
evolution of predators. A shell or mineralized covering would provide protection against
predation by the various predators evolving during this time. The conflict between predators,
whose goal is to consume prey, and prey, whose goal is to avoid becoming a meal for a
predator, is one of the strongest factors in natural selection.
4. A further line of research related to the Cambrian explosion involves what are known as
homeobox or, simply, Hox, genes. These are sequences of regulatory genes that control the
development of individual regions of the body, and thus the basic body plan in organisms.
Studies indicate that the basic body plans for all animals were apparently established by the
end of the Cambrian explosion, and only minor modifications have occurred since then