Rothbard introduces Herbert Spencer (1820-1903) in his essay “Herbert Spencer: Andreski & Peel”:

Herbert Spencer was a great and protean thinker, a self-taught genius who ranged over and systematically integrated vast realms of human thought: philosophy, politics, sociology, biology, and the other natural sciences. He was also one of the great libertarians in the history of thought, and his first, splendid work, Social Statics (1850) is still the best systematic exposition of libertarianism ever written…. Despite a few flaws, it stands today as a landmark, an inspiration, and a fountainhead of libertarian ideas. It was Spencer who coined the great libertarian “law of equal liberty,” and Spencer who penetratingly developed the vital contrast between “industrial” and “militant” (militarist) principles. Spencer’s seemingly naive optimism, his belief in the inevitable progress of mankind (in his early years) was undoubtedly overdrawn, but it rested on a sound insight that the free-market economy and the libertarian society were indispensable for the successful workings of an industrial world. Hence Spencer’s belief that, since society had been progressing in the direction of freedom and industrialization, it would continue to do so. Perhaps his optimism was only premature by a century or so.

Spencer, in short, more than any other figure, was “our Marx.” At the height of his career, in the middle and late nineteenth century, Spencer was acknowledged to be the greatest intellectual figure of his age, read and hailed widely by scientists, intellectuals, and the general public alike. Freedom-giant Henry Hazlitt referred to Spencer’s book, Man Versus the State (1884), as “One of the most powerful and influential arguments for limited government, laissez faire and individualism ever written.” In Hazlitt’s own Spencer-inspired book Man vs. The Welfare State (1969), Hazlitt writes:

…we are deeply indebted to Herbert Spencer for recognizing with a sharper eye than any of his contemporaries, and warning them against, “the coming slavery” [essay about socialism] toward which the State of their own time was drifting, and toward which we are more swiftly drifting today. …

In 1860, when Menger first attended the University of Vienna at 20 years old—23 years before Menger wrote the above—Spencer published one of his iconic masterpieces “The Social Organism” where we can see some of his brilliance, focus on what can only be called an “Organic Understanding of Social Phenomena,” methodological individualism, and likely influence on Menger:

…that societies are not artificially put together, is a truth so manifest, that it seems wonderful men should ever have overlooked it. Perhaps nothing more clearly shows the small value of historical studies, as they have been commonly pursued. You need but to look at the changes going on around, or observe social organization in its leading traits, to see that these are neither supernatural, nor are determined by the wills of individual men, as by implication the older historians teach; but are consequent on general natural causes. The one case of the division of labour suffices to prove this. It has not been by command of any ruler that some men have become manufacturers, while others have remained cultivators of the soil. In Lancashire, millions have devoted themselves to the making of cotton-fabrics; in Yorkshire, another million lives by producing woollens; and the pottery of Staffordshire, the cutlery of Sheffield, the hardware of Birmingham, severally occupy their hundreds of thousands. These are large facts in the structure of English society; but we can ascribe them neither to miracle, nor to legislation. It is not by “the hero as king,” any more than by “collective wisdom,” that men have been segregated into producers, wholesale distributors, and retail distributors. Our industrial organization, from its main outlines down to its minutest details, has become what it is, not simply without legislative guidance, but, to a considerable extent, in spite of legislative hindrances. It has arisen under the pressure of human wants and resulting activities. While each citizen has been pursuing his individual welfare, and none taking thought about division of labour, or conscious of the need of it, division of labour has yet been ever becoming more complete. It has been doing this slowly and silently: few having observed it until quite modern times. By steps so small, that year after year the industrial arrangements have seemed just what they were before—by changes as insensible as those through which a seed passes into a tree; society has become the complex body of mutually-dependent workers we now see. And this economic organization, mark, is the all-essential organization. Through the combination thus spontaneously evolved, every citizen is supplied with daily necessaries; while he yields some product or aid to others. That we are severally alive today, we owe to the regular working of this combination during the past week; and could it be suddenly abolished, multitudes would be dead before another week ended. If these most conspicuous and vital arrangements of our social structure have arisen not by the devising of any one, but through the individual efforts of citizens to satisfy their own wants; we may be tolerably certain that the less important arrangements have similarly arisen.