About 10 years ago, I had the opportunity to view a set of videos called "The Shape of Life." It was an amazing journey because it suggested that the earliest animal ancestor of human beings was the sponge. I watched this video several times, because I had trouble wrapping my mind around this finding. It was an excellent set of videos that I still highly recommend. The mind-boggling conclusion that we are descendants of sponges was reinforced in my mind back in November, 2004, when I read a fascinating article about our ancestors in discover magazine, pulling out the article: "This Is Your Ancestor." It is a story of an evolutionary microbiologist named Mitchell Sogin, who wanted to know the animal from which all other animals came. He extrapolated backwards from today's oldest known species: jellyfish, sea anemones, sponges, mollusks and starfish.  When he grouped each of these organisms according to their first appearance on Earth, the most likely candidate appeared to be the sponge. As the Discover article points out, sponges don't look much like animals, though they are truly animals, not plants, and there are 9,000 species of sponges on the planet.

Sponges are multicellular, but the cells don’t add up to much: no tissues, muscles, organs, nerves, or brain. But this simplicity can be deceptive. Some sponges come armed with glasslike skeletal spikes, microscopic and as beautiful as snowflakes. . . . Sponges are the earliest, most primitive multicelled animal, Sogin says. Some scientists believe the ability to grow different cell types started animals on the evolutionary road to becoming humans. With just a few kinds of cells, only loosely connected, the sponge manages to produce a variety of as symmetrical shapes, from cups and fans to tubes and piecrust shapes. Sponges survive handsomely on their own and can even shelter other sea creatures… Sponges are also the earliest sexual re-producers; most are hermaphroditic, producing both eggs and sperm which they release into the water.… Sponges don't just sit still-many actually move… One sponge moves 4 millimeters a day.

Sogin used an innovative ribosomal RNA analysis and he worked at it for more than 20 years. His conclusions are stunning:

The sponge was indeed at the base of animal lineage, and just above it were the cnidarians, such as jellyfish, anemones and corals. They, like the sponge, have a saclike body form. They developed tentacles and an opening like a mouth at one end. But there were other forms of life lower down the line of descent that scientists might not have expected. Suddenly, they made sense. One of the sponges cell types is the distinctively shaped choanocyte, a cell equipped with a tiny long filament, called a flagellum, surrounded by a collar studded with even tinier hairs called microvilli. Thousands of these flagella beat constantly at the water and move it past the sponges feeding cells. As it happens, Sogin found that the sponges' immediate evolutionary predecessors are the choanoflagellates, which represent what life would have looked like just before animals in the form of sponges emerged. Scientists had long suspected that the choanoflagellates could have been the nearest things to animals without actually being animals.

The Discover article then points out that the only thing older than the choanoflagellates in the same line of organisms are the fungi.  Sogin has determined that "fungi and plants are very different from each other, and fungi are actually more closely related to animals. [W]e share a common, unique evolutionary history with fungi." The same article points out that this common evolutionary heritage of fungi and animals explains "why fungal infections are so difficult to treat--they're more like us than we thought. They are similar targets." Therefore, the next time you see a sponge, show some respect, since sponges are the first multicellular animals, and "all the other animals emerged from this imple architecture and are built upon this platform." What animal would be find a bit upstream from sponges? Worms, another of our ancestors. Worms are "the first creatures with bilateral symmetry." The worm, along with fungi and sponges, organisms highly deserving of your respect because they are in your line of ancestry. For more about sponges, see my 2006 post titled "My Life as a Sponge." For a quick ride down the evolutionary highway, visit this post.