Question

The astonishing internal complexity characteristic of most animals became possible following the evolution of ______.

Options

• ectoderm

• myoderm

• mesoderm

• endoderm

Answer 1

The astonishing internal complexity characteristic of most animals became possible following the evolution of mesoderm.

Explanation:

The astonishing internal complexity of most animals became possible after the evolution of the mesoderm, which is the middle germ layer that gives rise to muscles, bones, the circulatory system, and other internal organs, enabling complex body structures and functions. This complexity is not associated with ectoderm, myoderm (not a germ layer), or endoderm to the same extent.