Recently, geneticists obtained a remarkable result: sponges, the oldest form of multicellular life known, can harbor between 18,000 and 30,000 genes, a range comparable to that of humans, fruit flies, roundworms, and many other animals. Since the sponge was taken from Australia’s Great Barrier Reef and I’m presently here in a conference, I felt compelled to reflect about this. Considering that sponges have been around for over 500 million years, possibly even a billion years, many scientists believe they form the base of the evolutionary branch in the tree of life that led to animals. In other words, don’t think of humans as coming from monkeys; we, and every other kind of critter out there, came from sponges, the cousins of the porous yellowy objects you use to scrub yourself in the shower.
It may be a bit strange to think of such simple beings as our ancestors. After all, sponges don’t have skin tissue or nerve cells. However, sponges do have genes that can encode the proteins that nerve cells use to communicate or the ones needed for skin tissue. It’s all there, even if in some kind of inactive, dormant state.
Apart from being a fabulous demonstration of the investigative power of modern molecular biology, the discovery brings out another interesting point. If sponges had all this genetic apparatus over half a billion years ago or even more, where did it come from? If one adopts a reductionist approach to the evolution of life, it’s natural to suppose that the first life forms were simple, that is, they had a small number of genes. The jump in complexity from a few genes to thousands is highly nontrivial.
Creationists are going to love this.
“Ha!” they’ll say with glee, “how could something like this happen without the agency of purposeful engineering? Clearly, there was some serious tweaking with primitive life forms to get to this level of complexity.” I predict that the argument for the implausibility of the eye will be taken a notch further down the evolutionary ladder.
Biologists, and I hope my distinguished co-bloggers will come in to say hi and set me straight, should easily dismiss any of this nonsense. There is something fundamentally perverse in using scientific evidence at hand as proof of a final argument. What I mean is that one cannot take the data known at present as all the data that can be gathered in order to make a definitive statement. In science, data gathering is an on-going process. Darwin was also attacked for the “missing links” in the fossil record. People wanted a continuous, movie-like progression of life forms, without the jumps that necessarily exist.
This kind of continuity is impossible for at least two reasons. First, there is no way that fossils from all species that existed in the past should have been preserved all the way to the present. Some would decay and others could never fossilize. And even if they could have been preserved, finding them all is virtually impossible; some are forever lost in the depths. Second, there is the punctuated equilibrium hypothesis of Niles Eldredge and Stephen Jay Gould, according to which life evolves in tandem with Earth’s environmental drama. Huge cataclysms, from asteroid impacts to massive volcanic eruptions, could have disrupted life so as to act as an effective reset button. Given the abrupt change in conditions, there would be a necessary discontinuity: only the real freaky mutants would survive…
In other words, taking the genetic complexity of sponges as evidence for purposeful tampering is like getting to a movie halfway and refuse to admit you missed half of it. Since they lack a skeleton, sponges and jelly-like species don’t fossilize. So, it’s quite plausible that what we are able to see now is only half the movie. Probably, there were simpler life forms, even multicellular ones like proto-sponges, with a smaller number of genes. The jump in combinatorial possibilities as the genetic code becomes more complex is highly nonlinear.
As in archeology and in cosmology, we have to accept the fact that we will never watch the whole movie. Scenes will always be missing, and the challenge we face is to make sense of the past with only fragmented information. The beauty of science is that we can.