Can death ever be a good thing from an evolutionary perspective? Even though natural selection is all about survival and reproduction, the death of individual cells within a multicellular organism can be beneficial. For example, as the organism grows or when in stressful environments, some cells are no longer needed. Without the ability to kill off such cells organisms suffer. Indeed, such an inability leads to cancer. And so it is not surprising that plants and animals regularly kill off unneeded cells. In fact, their cells have an elaborate and sophisticated programmed cell death (PCD) apparatus. When the signal is given an amazing process of dis assembly begins where the cell's molecular structures are chopped up in an orderly manner. Like the engineers who know just where to dynamite a bridge, the PCD apparatus destroys the cell with remarkable efficiency.
PCD is yet another example of biology's elaborate and sophisticated designs that evolution struggles to explain. But new research has added yet more trouble for evolution. It turns out that PCD in plants and in animals have some similarities that further indicate, from an evolutionary perspective, that PCD was present in the common ancestor of plants and animals.
But the common ancestor of plants and animals was not a multicellular organism--it was a unicellular organism. Why would evolution design a cell that can kill itself?
It is yet another example of an evolutionary expectation gone wrong. And, in turn, evolutionists will react with another silly just-so story. Perhaps it will go something like this:
Competition for resources was fierce even in the early phases of evolutionary history. Before cells aggregated to form multicellular life, they existed in tightly knit communities, which provided various benefits including easier defense against predators, reduced susceptibility to environmental threats, and the facilitation of resource sharing as an insurance against the spatial or temporal resource famines that cells going it alone might face.
The cost of such cellular communities was that particular cells may need to be sacrificed occasionally for the good of overall community. For instance, perimeter cells facing environmental threats would have an increased chance of death and so their resource consumption would be inefficient. Better for them to cease consumption and conserve resources needed by the remainder of the community. Also, cells in the crowded interior of the community may occasionally face resource deficits and, again, cell death would improve the fitness of the remainder of the community.
These scenarios parallel the altruism that has been observed in insect communities, and there is no reason such evolutionary dynamics were not present in the unicellular world. This is an instance where evolutionary theory sheds light on itself, as what we learn about the evolution of observable extant species may apply to the evolution of unobservable, deep-time, species.
Of course the evolution of unicellular PCD relied on environmental signals to initiate the PCD. Such signals could not be too predominant or community wide, for they would have the potential to kill off the entire community. Nor could the PCD signaling be too rare. Most importantly, of course, the selected PCD signals would need to correlate with threats and stresses that could be countered with PCD. Resource concentration reduction is an obvious candidate PCD signal, but our research investigates several other, more subtle and more discriminating, environmental signals which could have led to the evolution of PCD in early life.
See how easy bad science is? One could get used to it.
