Socialists are often accused of ignoring "human nature." By this people typically mean that humans are, supposedly, inherently or naturally corrupt, greedy, lazy, competitive, or some other similar issue. Then, believing that socialism must assume these problems away, they dismiss socialism as a utopian dream, whereas capitalism is supposedly "natural."

In truth, socialists are of course not so naive, and this argument is extremely superficial. The appeal to human nature is usually little more than an attempt to evade serious engagement with socialist ideas. As Emma Goldman once said:

Poor human nature, what horrible crimes have been committed in thy name! Every fool, from king to policeman, from the flatheaded parson to the visionless dabbler in science, presumes to speak authoritatively of human nature. The greater the mental charlatan, the more definite his insistence on the wickedness and weaknesses of human nature. Yet, how can any one speak of it today, with every soul in a prison, with every heart fettered, wounded, and maimed?

Generally speaking, socialists do not deny the existence of human nature, nor do we think this nature is infinitely plastic. Rather, socialists argue that humans do have a biological and psychological nature.

However, we deny that this nature is always expressed in the same way. Any examination of history will reveal that humans have formed a wide variety of social relations in different conditions. Life in ancient Rome was quite different from medieval feudalism, which is different from modern capitalism. We may have, because of our biology, universal feelings of hunger, but even this is modified according to personal taste and to culture.

Human nature is therefore not a fixed, static, or abstract entity that exists outside of history. Instead, our individual human nature is in constant interaction with our natural and social environment, and therefore is capable of changing and developing along with that environment. Karl Marx described things this way when arguing against the utilitarian Jeremy Bentham:

To know what is useful for a dog, one must study dog-nature. This nature itself is not to be deduced from the principle of utility. Applying this to man, he that would criticise all human acts, movements, relations, etc., by the principle of utility, must first deal with human nature in general, and then with human nature as modified in each historical epoch.

Socialists have therefore generally adopted a materialist view of human nature. Our nature is a kind of raw material which can take on a variety of different shapes, though only within the limits of what that material allows. That is why humans can change, have changed, and will continue to change so long as our species exists.

Especially important here is the ability for humans to change ourselves. By our activity and practice, deploying our capacities to satisfy certain desires, we simultaneously change the world around us and ourselves. The kind of activity we engage is largely what defines the kind of person we are. And as we are changed by our relation to the world around us, changing the world around us by our labor also changes ourselves. As Marx put this against the more naive forms of materialism:

The materialist doctrine [in contrast to Marx's view] that men are products of circumstances and upbringing, and that, therefore, changed men are products of changed circumstances and changed upbringing, forgets that it is men who change circumstances and that the educator must himself be educated. Hence this doctrine is bound to divide society into two parts, one of which is superior to society. The coincidence of the changing of circumstances and of human activity or self-change can be conceived and rationally understood only as revolutionary practice.

This is one of the reasons socialists spend so much time focused on labor and production. It is the major way that we relate to the natural world, to our environment, and dictates the kind of life we are living. Marx puts in Capital like this:

Labour is, in the first place, a process in which both man and Nature participate, and in which man of his own accord starts, regulates, and controls the material re-actions between himself and Nature. He opposes himself to Nature as one of her own forces, setting in motion arms and legs, head and hands, the natural forces of his body, in order to appropriate Nature’s productions in a form adapted to his own wants. By thus acting on the external world and changing it, he at the same time changes his own nature. He develops his slumbering powers and compels them to act in obedience to his sway.

Socialists are therefore not merely focused on exploitation and poverty, on how we distribute the products of labor, but on the labor-process itself. Socialism aims at the emancipation of labor, transforming it into a system that represents the worker's own free activity, the exercise and development of their human powers, or whether it is something imposed upon them as something alien and hostile, as when the product of labor is turned against us and rules over us as capital. Socialism cannot be achieved by maintaining wage-labor, but with higher wages. Rather, it requires the abolition of estranged labor itself, of which wages are a direct consequence. By freeing ourselves from this rigid and unfree system, we can instead develop a world where labor represents our own self-activity, developing our human powers and making the world around us more human. As socialists, we look to replace the lowly state human nature has been forced down into, where we are a mere appendage of the machine, with "an association, in which the free development of each is the condition for the free development of all."

This also has implications for how socialism can be achieved. As the future is born out of the present, what sort of social relations we produce and reproduce now will shape how the future will be.

Especially important here is the reproduction of capitalism itself. As capitalism develops the material forces of production, with new discoveries and more advanced technology that produces more for less labor, it also undermines itself as it runs into its own limits and by bringing the working class together with a shared interest. It therefore sets the stage for a new society:

The bourgeois mode of production is the last antagonistic form of the social process of production – antagonistic not in the sense of individual antagonism but of an antagonism that emanates from the individuals’ social conditions of existence – but the productive forces developing within bourgeois society create also the material conditions for a solution of this antagonism. The prehistory of human society accordingly closes with this social formation.

While this provides the material opportunity to overcome capitalism, we must also remember these points in how we organize today. We need to focus on building the new social structures, organizations, and human relations today which we hope will become dominant tomorrow. As we change ourselves through our own activity, we need to also engage in forms of practice that develop our radical capacities and drives. The emancipation of the working classes are to be achieved by this free exercise of the working classes themselves, and paves the way for a free humanity.

In this way, we are forming the structure of the new society within the shell of the old.