In Search of the First Animals


All animals–from corgis to Greenland sharks, from dog ticks to toucans to you–descend from a common ancestor. The fossil record of animals, which runs back over 600 million years, can help us travel back some of the way through animal evolution towards the origin of the kingdom. But those early rocks contain precious few remains of animals, and so fossils alone can’t tell us what our common animal ancestor looked like.

Scientists can add to their supply of clues by studying living animals. And it now looks as if some of the most important clues to how animals got their start come from a beautiful creature called the comb jelly. This video from the Monterey Bay Aquarium is a good introduction to their luminescent loveliness.

In the past, a lot of scientists would not have put so much importance on comb jellies. If you asked them (as I did) how animals evolved, they’ve sketch out a version of events that runs like this:

1. Before multicellular animals evolved, their ancestors were single-celled protozoans that may have formed colonies. Our DNA shows that our closest non-animal relatives are critters called choanoflagellates. I wrote about our single-celled cousins in the New York Times.

2. Our ancestors then crossed the line from colonial life to life as multicellular creatures. They became the first animals.

3. The animal lineage then started to split into new branches. Many branches are now extinct. Among living animals, the first split divided the ancestors of today’s sponges from all other species.

Written By: Carl Zimmer
continue to source article at


  1. From my layman’s point of view, it seems like the majority of genetic comparisons confirm phylogenetic trees based on morphology, with a slight readjustment here and there. But this is quite a big one isn’t it?

Leave a Reply