I am still awed by the heroic stories of Wesley Autrey and Sergeant Tommy Rieman, both of whom were honored by the President during his State of the Union address. This is a level of altruistic behavior that far surpasses the one exhibited by social insects.
In insect society, altruism is enforced and deviation from the altruistic norm is punished. A worker bee has perfectly functional ovaries but will refrain from laying eggs and will devote her life to foraging, for the good of the community. Eggs laid by the occasional rebellious worker will be simply eaten by other members of the community. So, what’s the point? She might as well obey the rules. Yes, a bee will also sacrifice her life in defense of the hive by stinging the aggressor and leaving the sting in his body and die. This behavior, however, not volitional, is totally automatic, fueled by nerves, hormones, and pheromones.
The evolutionary roots of altruistic behavior
Obviously, we can only speculate on “how did it all start?”; what is the biological matrix that allowed this phenomenon to take shape and come to its ultimate expression in a soldier shielding his buddy from machine gun fire with his own body?
My own pet theory is that it all started with cooperation, and that is a truly ancient trait of living organisms. There is much suggestive evidence that the beginning of life on earth was in the form of unicellular organisms swimming in a primordial soup. Most likely, individual cells bumped into each other quite randomly and stayed stuck together by virtue of their oily, lipid membranes. As the number of cells in this agglomeration increased, different cells found themselves in different environments. Some were located in the interior, others in the outer layer, and still others in between.
These shapeless, “dumb” blobs could have lived happily ever after if not one, or several, of them began to have cells that performed some functions better than their neighbors, while other functions were performed better by the neighbors. For example, it is quite plausible that some outer cells that possessed flagella (little whips) or cilia (little hairy projections) were better at swimming or collecting more food by beating and directing the surrounding soup to the interior of the agglomerated mass. And if some cells in the interior had a somewhat better capacity to take in the soup, filter it, and retain some nourishing substances, and maybe somewhat later “learn” how to digest them, then we have division of labor—and this is not a shapeless mass of cells anymore, it is a colony. Or a society, if you will.
As the division of labor advanced and specialization deepened, cells became less and less “individualistic”, so to speak—looking after their own interests, and more and more “selfless”. Of course, I am anthropomorphizing here, but it makes the point. In this environment, it does not take a great stretch of the imagination to speculate that some cells would specialize to sacrifice themselves for the good of the colony. Is there any evidence for this wild speculation?
Those amazing neutrophils
When we are invaded by microbes (and we are indeed constantly under attack), our first line of defense is white blood cells, called neutrophils.
They will engulf, swallow, and kill the invaders, and normally will die within 24 hours after performing this lifesaving act. Coming to think of it, this has the ring of altruistic behavior to it. But there is more.
Arturo Zychlinsky and his colleagues from the Max Planck Institute in Berlin have published a fascinating report in the January 22nd issue of the Journal of Cell Biology (Fuchs et al, J. Cell Biol. Vol.176, pp. 231-241, 2007). They describe a newly discovered mechanism of neutrophilic defense; I would call it the Samson Defense. This playboy of the Eastern world was blinded and tortured by the Philistines. But rather than endure the indignity, he used his great physical strength to bring down the temple upon himself and his tormentors. The neutrophils do the same.
While many of the neutrophils simply perform their duty in the conventional way by engulfing and internalizing the invaders, others, for unknown reasons, commit suicide and take the invading hordes with them.
How do they do it?
Fuchs and his colleagues observed that the process begins by the breakup of the nuclear membrane. Once this is accomplished, the nuclear chromatin (the material that makes up the chromosomes, DNA, and its protein coating) leaks out into the cytoplasm. While this is happening, the membranes that surround granules that reside in the cytoplasm disintegrate as well. These granules are deadly to microbes; they are made up of enzymes that wreak havoc with their structure and kill them. The chromatin now binds with the granules and together they organize themselves into a mesh or network.
Finally, the neutrophil’s cell membrane disintegrates and the mesh gets outside the cell, or more accurately, the ghost of the cell since it had died when all its internal structure disintegrated. But the mesh serves as a trap for the microbes. Once they get enmeshed in the sticky net, the deadly enzymes of the granules finish the job.
So there you have it. A cell sacrificing itself, with no benefit for itself, for the good of the “society” of cells that make up the organism. It keeps fighting the invading microbes after it has long died. And it doesn’t even get a silver medal or a purple heart for this heroic feat.
Just think of it: Here is an unbroken, albeit mechanistically ever more complex, line of courageous and selfless behavior that started in some lowly cells close to a billion years ago, became a part of us hundreds of thousands of years ago, and somehow led to the heroic sergeant—fascinating and awe-inspiring.