IN MIDSUMMER, many insects acquire the power of flight, and swarm out to pair. Vast numbers fail to be fertilised, and perish. In the same way these unicellular organisms swarm out, free and unhindered, each striving with all its might to be the parent of a new generation.
They are like a lot of factory hands in a big city, hardened by rough usage; deafened by the ceaseless noise; blunted by the endless monotony. They are all tied to their own trade and their own job. Only a few of them retain their original humanity and geniality. And yet these wheels in the industrial machine, and indeed all of us, sprang, long, long ago, from all-round men who lived a natural life, formed family groups to fight the battle of life for themselves, hunted or cultivated their food in the open air, acquired knowledge, not from books or newspapers but from their own experience of life, cured themselves when they were sick, and comforted themselves when they were sad or terrified.
This illustration from the history of the human race gives a clear picture of the evolutionary history of cell-life too. Our adult cells have long since forgotten that the primordial cells, from which in the course of evolution all higher species have developed, had to perform all functions, though in an elementary fashion, for themselves. In these unicellular organisms each cell had the power of changing its position, of ingesting food, of excreting waste-products, of growth, and division. If the two cells resulting from such a division became quite separated the division was equivalent to reproduction.
It is very different now. In our multicellular organisms, all the cells of which that gigantic cell-colony, our body, is composed, have long since lost this plurality of function, and become altered in various ways. They have become specialised to fulfil various special functions. The cells of the epidermis have become horny to form a covering, the skeleton has become hardened to form a support, the muscle-cells have become woven into elastic strands for the purpose of movement, the whole and all its parts are surrounded and joined together by connective tissue. We have quite forgotten the autonomy and independence of the single cell; we can no longer realise it.
But now, when we see this new generation of unicellular organisms swarm out from the profoundest depths of our being, we are once more reminded of it. We are transported again to that primitive period, the period of unicellular organisms. There is a new generation of free-born single cells, consisting of almost fluid protoplasm, possessing the same embryonic character as the cells from which the whole course of our evolution began, as yet quite undifferentiated for special functions, a raw material still young and available for any purpose.
These cells, however, are too delicate and too feeble to be able to continue their existence independently. In the first rapture of the nuptial flight they pair at the earliest opportunity. So they double their energy and their useful elements by conjugating in couples.
But the fertilised egg-cell (zygote) at first still requires parental care, in order that a multicellular organism may develop by vegetative cell-division from the unicellular organism.
So the history of evolution continually manifests periodicity, an alternation of generations, first a sexual generation of unicellular organisms, then a vegetative generation of multicellular organisms. The life of these unicellular organisms is brief, but full of bliss; it is a nuptial flight. Then again follows a vegetative period of growth which naturally lasts far longer.
Man, however, has no simple structure of vascular bundles and no axillar defects like plants. The possibility of regeneration after wounding is very limited. We may be glad if our wounds even heal up. In man, it is solely the sexual reproductive cells which have undertaken the reproduction of the species. They can only do so by swarming out.