The last common ancestor of all animals was probably a _____.

• A. flagellated protist
• B. unicellular fungus
• C. multicellular plant
• D. photosynthetic bacterium

Answer: (A)

Verified step by step guidance

1. Understand the question: The problem is asking about the last common ancestor of all animals, which requires knowledge of evolutionary biology and the characteristics of early life forms.
2. Recall that animals are part of the domain Eukarya, which includes organisms with complex cells containing a nucleus and organelles. The ancestor of animals must also belong to this domain.
3. Consider the characteristics of early animals: Animals are multicellular, heterotrophic (consume organic material for energy), and lack cell walls. Their ancestor would likely share some of these traits but may not yet be multicellular.
4. Review the evolutionary relationships: Molecular and fossil evidence suggests that animals evolved from a group of protists called choanoflagellates. These are flagellated protists that are unicellular or colonial and share similarities with the cells of sponges, the simplest animals.
5. Conclude that the last common ancestor of all animals was most likely a flagellated protist, as this aligns with the evolutionary evidence and the characteristics of early animal life forms.