How Scientists Think About the Limits of Evolution
Darwin's theory showed how natural processes could give rise to a diversity of life that had previously appeared inexplicable – even magical. With natural selection, scientists suddenly had a unified framework within which to understand the anatomy and behavior of living things. But a couple of looming questions remain unanswered even today. How did life begin? And how and why did cells give up independent living and start glomming together into complex organisms like us?
It would be misleading to view either of these open questions as signs of a fatal flaw in the theory of evolution by natural selection. Einstein's theory doesn't explain everything in physics, either, which is one of the reasons there are still jobs for physicists.
I'm near the end of an intense, week-long meeting in which scientists from different disciplines are converging from around the world to consider this question of how and why single cells started to cooperate. It's not just a matter of cells sticking together – in us they also have to abide by a division of labor. Some cells become bone, some muscle, some neurons, and only a few, the eggs and sperm that are able to live on in a new generation.
There are lots of different approaches people are bringing to the table. Some are studying life forms with only a few different kinds of cells, such as a type of algae called volvox. Others look at slime molds and certain types of social bacteria and amoebae that can live independently, then form structured, plant-like stalks, and then go their separate ways again.
The conference is called Cooperation and Major Evolutionary Transitions – a title that reflects the current thinking that there's a connection between different types of cooperation, whether among cells in our bodies, bees in a hive, or employees in corporations.
Despite the popular association with Darwin's theory and competition, "red in tooth and claw", his concept of natural selection can explain a host of selfless behavior once 20th century scientists added genes to the picture.
Looked at from the point of view of the genes, all kinds of altruistic acts started to make sense – a gene that endowed parents with the urge to protect offspring might survive and flourish over rival genes that did not, since their well-protected offspring would stand a greater chance of living long enough to pass those genes on.
This gene-centered view was what Richard Dawkins popularized in his 1976 book The Selfish Gene. Many people reacted negatively to the title and never read enough to realize that the book shows how natural processes alone can give rise to selflessness. The scientific concept at its center is often called kin selection because altruism is connected with shared genes – and we share the most genes with our kin. The cells within your body are the ultimate kin since, for the most part, they share all the same genes.
What I've learned at this conference is that science is pretty good at explaining how cooperative groups of animals or cells can keep from falling apart, but it hasn't done as much to explain how these groups form in the first place.
There's still no complete story of how single-celled organisms make the leap to becoming cells that cooperate to form a body, working together as a cat or oak tree or mushroom. Scientists see evidence that such a "transition" to multi-celled living happened at least 25 times independently in the history of life. In most living things with a variety of cells, there are special "germ" cells that retain the ability to start a new individual. They alone can live independently. But how do they know to start making a new animal or plant rather than just reverting to their ancestral state of free living?
One thing that's agreed upon is the answers will work within a Darwinian framework. Something new may come into the picture, but it will be a natural process, not a supernatural one. There are always going to be gaps in science, and attempting to plug them with "intelligent design" or other supernatural answers only serves to halt inquiry.
And so as we approach our next Darwin day later this month, it's important to remember that it's not a battle of one type of dogma over another. No form of creationism offers a scientific alternative to evolution. Schools should teach the current state of knowledge not because it holds all the answers but because it holds the best answers we have to date, and because the current state of science tells us where to launch new investigations. The task of understanding the world is far from over.