Unlike the herd of gnus, a flock of Merino sheep does its grazing on a more or less confined area. It is kept there by shepherds and their dogs, and depends on some human assistance at lambing and for shelter and fodder when the winter is too hostile. Man repays himself with wool and meat with some breeds being better at furnishing wool, others meat. Two Merino ewes of the same age look much the same, but a Merino is very different from a Blue-Face Leicester and from other breeds of only a little less charming names. The two breeds, and others who bear less charming names, specialise in somewhat different products and are adapted to different habitats (though the Merino can put up with almost any climate and miserable pasture).
Neither the herds of gnu nor the flock of sheep has any social structure to speak of; all individuals of the same age and gender are of equal rank and have equal access to the available grazing. Packs of wolves do have a social structures of sorts, but few animals are hierarchical. Neither species is acting purposefully to create or improve its own habitat. Apart from moles, foxes and badgers who burrow underground lodgings where the environment above ground suits then, the only habitat-builder animal is the beaver who makes lakes.
On the whole, the animal kingdom is characterised by great homogeneity, physical and behavioural uniformity within each species. This is, of course, what the evolutionary origin of the species, demonstrated by Darwin and his successors, leads us to expect. It is much less clear whether we should also expect the passive adaptation of each species to its environment and the almost total absence (except in the beaver?) of deliberate attempts to alter and control it. Improving its environment by ploughing the waste land, clearing the bush, controlling and displacing the waters, and breaking paths for others to use, is typical only of one species: mankind. So is its tendency to have a social structure that is getting more elaborate as time passes.
Scientists and philosophers over the ages have amused themselves with proposing answers to the question: what essentially makes man a man and the animal an animal? Some of the answers—the sense of ridicule and of humour, shame, modesty, the privacy wanted for sex, forethought, a propensity for metaphysical thought—are interesting though not overwhelmingly strong. One that the present article commends is diversity within the species. A pair of young women randomly chosen, not from humanity as a whole or a nation, but from among the young women of a small town, is probably impossible to mistake for identical twins. The two women will be incommensurately more different from one another than the randomly chosen members of a pair of animals of a given animal species. If we add to physical characteristics the ways of interaction with others and a host of other things that only humans do man is more diversified by several orders of magnitude than any species of animal. The scope for a variety of social organisation and cooperation to evolve, compared to the much less varied scope for the same even within such a collaborative but un-diversified, uniform animal species as the ant or the bee, is enormous.
Curiously enough, there is a strong propensity in human thought to hold that for one reason or another, the material rewards accruing to men and women of widely and even wildly different capacities, talents and efforts should differ but very little, perhaps not much more than the grass one gnu manages to eat compared to the amount every other gnu grazing next to it gets to eat, always bearing in mind that one gnu is not noticeably cleverer or more intent on finding grass than the other.
Judaism and early Christianity insisted on equality of material wellbeing—in practical fact, equal poverty achieved by intense charity—is a moral rule religion orders us to obey. The sort of supporting argument, namely that God created all men equal was flagrantly contrary to evidence and experience, but held sway for many centuries. With its decline after the Enlightenment, two lay doctrines gained preponderance, Benthamite utilitarianism and Kantian "rightsism". One led to the egalitarian streak in welfare economics. The other to a soft-Left political philosophy characterised by appeals to social contracts and is also egalitarian. By the end of the 20th century, both these doctrines lost their shine as their logical basis was proved to be faulty, though like other outdated doctrines, their trace is still deeply marked in the habits of thought of the average intellectual. However, their place in the vanguard has oddly enough, been taken by evolutionary game theory. Oddly, because the popular view of Darwin and Darwinism has long used to be that he was only a little better than the devil, his teaching was cynical, cruel, and immoral and gave a pseudo-scientific licence to a capitalist free-for-all, survival of the fittest and the devil take the hindmost. Much to the surprise of some of us, we are now taught that evolutionary equilibrium is egalitarian and is really a set of benign social contracts in a kind of genetic disguise, yet entirely empirical and untainted by metaphysical affirmations.
Throughout all but the tail-end of pre-history, most of humanity eked out a precarious living by hunting game and gathering edible plants. We might say, by way of causal explanation, either that most of humanity recognised and chose hunting-gathering as the most efficient survival strategy, but equally well we might say that because hunting-gathering was the most efficient survival strategy, those who chose it eventually became the majority by way of their genes being transmitted to their descendants while the genes of the ones who had opted for another way of making a living, ill-adapted to the available environment, died out with them. Genes mutate, some of the new genes predispose to a wandering, others to a sedentary existence, but the latter get less of a chance to transmit their predisposition than the former, hence the hunter-gatherer dominance.
In the small hunter-gatherer band, members had unequal day-to-day success in hunting and gathering, but shared the meat, the berries and mushrooms equally. Techniques of preserving food were poor and carrying along stocks of preserved food were both awkward for the wanderer and unsafe if only some of the wanderers had such stocks while the rest went hungry. Hence the best use of the food was "share and share alike", the egalitarian rule. Sir Ken Binmore, the distinguished game theorist and philosopher, is convinced and would convince us that this rule, originating a very long way in pre-history, is "hard-wired" in us to this day and appears as the notorious "original position" in Rawls's Theory of Justice. Equal distribution, then, is not a utilitarian recommendation nor a moral imperative, but an empirical matter of genetic evolution.
It so happens, though, that in the last ten thousand or so years B.C., initially in Mesopotamia and the Nile Valley and subsequently over ever larger areas, the technique of sowing grain, waiting for its harvest and preserving some of it from one season to the next has proved vastly superior to hunting-gathering and radically replaced it. Moreover, the genetic survival of the sedentary agriculturist was not best served by share-and-share-alike. With other things equal, the hardest-working and cleverest agriculturist was more likely to produce a surplus to be saved and stocked than the less efficient, lackadaisical and unskilful one. The former, by accumulating and not sharing grain, had a better chance of safely raising his progeny than the latter. Like it or not, "selfishly" individualist maximising behaviour became the winner in the evolutionary process. Egalitarian distribution turned out to be obsolete as a survival strategy, and the "original position" had to fall back on some metaphysical affirmation for support.
For more on these topics, see the EconTalk podcasts Robert Frank on Inequality and Bruce Meyer on the Middle Class, Poverty, and Inequality. See also Distribution of Income, by Frank Levy, in the Concise Encyclopedia of Economics.
However, once individual maximisation and accumulation by the most successful has become the dominant evolutionary conduct, in most of the contemporary world there followed an accelerating capacity to produce wealth, undreamt of a mere century or two ago, as did the risk by environmental degradation or nuclear war. Share-and-share alike is a nostalgic ideal of some of us; persistent attempts to impose it on contemporary societies by the use of a collective choice rule that is almost pre-destined to favour it, cripple the wealth-creating capacity and probably leave the risks of great damage intact. Whether they make for a better world or a worse one is the sort of futile "what-is-the-meaning-of-life" kind of infantile question to which Buddha is reputed always to refuse to answer, an attitude we should respect and probably ought to imitate.
A million gnus, all alike and sharing the grass more or less equally, have never tried a different way of life, never started off a dizzying gnu civilisation and no one can say that they have lost something by leaving well alone. In any case, being all alike, they hardly had a choice in the matter. Mankind, a species of unparalleled diversity, has developed a civilisation in an accelerating rush and has hardly a choice in the matter. Trying to exercise a choice now and impose reversion to a distributive equality looks like a great mistake we shall one day soon learn to regret.