How might a materialist and a Marxist today describe the human body?
It has been commonly understood that the theory of historical materialism proposed by Karl Marx is a psychological theory having to do with "man's drives and passions" and teaching that man's "greed for material satisfaction" is the driving force of history. However, scholar Erich Fromm (1961) points out that the above is actually a common misinterpretation of Marx. Instead, Fromm asserts that Marx did not view historical materialism as a psychological theory; instead, Marx uses historical materialism to propose an economic theory of production. According to Fromm, Marx argues that "the way man produces determines his thinking and his desires"; he does not propose that our "main desires are those for maximal material gain" ("Marx's Historical Materialism").
Since Marx's philosophy of historical materialism isn't based on material gains, he also doesn't define the human body as moving expressly for the sake of material gains. Marx asserted that "nature is man's inorganic body" (World Socialist Organization, "Karl Marx: Anthropologist"). It's also important to understand that Marx saw human beings as "active, living beings" who feel sensations, can think, and feel emotions, but he also saw human beings as being limited in what they can do and prone to conditioning and suffering ("Karl Marx"). Hence, in saying that "nature is man's inorganic body," he is saying that there is a direct interrelationship between man and nature. It is through man's interaction with nature that he produces things to fulfill his material needs, and the more mankind is able to successfully produce through labor, the more he is a happy, productive, and well-rounded human being.
Hence, according to Marx, the human body is a movable, thinking, feeling essence that does not act, or produce, simply to fulfill its material needs; instead, the way in which it produces directly influences the needs and thoughts of the human body. If we were to phrase this in terms of modern-day thought, we might say that the human body is designed to be able to fulfill any occupation, such as being a student, and fulfilling this occupation directly influences thoughts and feelings. For example, the more a devoted student studies and learns, the more the devoted student has a desire and need to study and learn.
In contrast, Marx objected to the "vulgar materialists" who reduce all of existence to simply material existence, to simply matter (University of Hawaii, R. J. Rummel, "A Humanism Between Materialism and Idealism"). Materialists believe that everything can be explained in a cause-effect relationship and that even our thoughts are simply "complex chemical reactions taking place in the brain" (New World Encyclopedia, "Materialism"). Hence, the materialists believe that even matter shapes our thoughts.
Therefore, in contrast to Marx, the materialist would see the human body as being composed of matter, such as molecules, and that what we perceive to be our thoughts and feelings are really just chemical reactions to the matter we interact with. Furthermore, the human body's sole aim is to interact with matter to fulfill greedy bodily needs. If we were to phrase this in terms of modern-day thought, we might say that the human body is built to acquire possessions, and the more we acquire those possessions, the more our thoughts and feelings are shaped.