by SEAN B. CARROLL
“Recent studies suggest that choanoflagellates are cousins to all animals in the same way that chimpanzees are cousins to humans. From left, a choanoflagellate colony, feeding cells of sponges that resemble choanoflagellates and a choanoflagellate with its long flagellum and collar of filaments. There can be millions of choanoflagellates in a gallon of sea water.” PHOTOS/Mark Dayel & Scott Nichol
For most of the first 2.5 billion years of life on Earth, most species were microscopic, rarely exceeding one millimeter in size, and unicellular. Many different kinds of larger life forms, including fungi, animals and plants, subsequently evolved independently from separate single-celled ancestors.
…
Scientists are eager to understand how transitions from a unicellular to multicellular lifestyle were accomplished. Reconstructing events that happened more than 600 million years ago, in the case of animals, is a great challenge. Ideally, one would have specimens from just before and immediately after the event. But the unicellular ancestor of animals and those first animals are long extinct. So information has to be gleaned from living sources.
The New York Times for more