What type of protists are considered the ancestors of animals?

Protozoa are considered the ancestors of animals due to their cellular organization and evolutionary history. They are primarily unicellular organisms that share several key characteristics with early multicellular animals.

The evolutionary lineage of animals is believed to trace back to single-celled protozoans that lived in aquatic environments. Certain groups of protozoa, such as choanoflagellates, are closely related to the most basal forms of animal life and display similarities in cellular structure and method of feeding with early multicellular organisms. This close relationship is further supported by molecular studies, which show that animals and choanoflagellates share homologous genes and have similar cell types.

In contrast, plants and fungi represent entirely different evolutionary branches. While both groups are important in their own right, they originate from different ancestral lines and do not share the same lineage as animals. Algae, though they are photosynthetic and play a crucial role in ecosystems, are not direct ancestors of animals and are more closely related to plants than to the animal lineage. Thus, focusing on protozoa illuminates the evolutionary connections that link them as the ancestors of animals, highlighting their significance in the context of evolutionary biology.