The powers most frequently associated with natural man, with human beings as living parts of nature, are labor, eating and sex. Marx never drew up a full list of man's natural powers; nor is he concerned to remove the verbal cloak which hides some from public inspection. What he labels a ‘natural power’ in one place is referred to as an ‘animal function’ or a ‘physical need’ in another. These expressions are not exact equivalents, but they are so closely related that we may take the examples Marx offers for any one as examples for the other two. Animal functions are the processes that living creatures undergo and the actions they undertake in order to stay alive; while physical needs are the desires they feel for the objects and actions required to keep them alive and functioning. With certain qualifications drawn from our earlier discussion, we could say that natural powers are similar to animal functions and the relation between both of them and physical needs is similar to the relation between power and need. When Marx refers, therefore, to drinking and procreation as animal functions, we are justified in adding them – assuming we want to distinguish between procreation and sex – to our list of man's natural powers.

Marx's reference to the needs of animals and savages can be viewed in the same light as his reference to physical needs; both reflect natural powers.