The drums in the novel share a close link with the title. Drums are symbols of the rhythm of life. Their beat can be equated to the beating of a heart. Since the heart is central to our survival, its beating indicates that we are alive and once it stops, we die. The drums in the novel also signify the heart of the jungle. Its beating indicates that there is life and once the drums go silent, life has ceased.
In terms of the themes of greed and destruction depicted in the novel, the drums become an apt symbol for those who have become victims of so called civilized man's lust for material wealth. Drums are a token of their civilization: it is the means by which they communicate, celebrate, praise and show obeisance to their gods. If their culture is destroyed, the drums also die.
Furthermore, the drums symbolize the natives' distinct contrast to those who have invaded their culture and have come to oppress them. The invaders see them as primitive, uncivilized and savage. They arrogantly believe that they are introducing them to a better way of life when, ironically, they are the true savages for brutally oppressing, enslaving and exploiting those whom they have supposedly come to save.
In addition, the drums are a symbol of humankind's most basic nature. It signifies our own, inherent savagery, so aptly depicted in the novel. Once we are removed from so-called civilized norms, we too, become savage for we are, at the deepest level, innately feral.
The narrator, Marlowe, shares his sentiment about the drums in part one when he says:
Perhaps on some quiet night the tremor of far-off drums, sinking, swelling, a tremor vast, faint; a sound weird, appealing, suggestive, and wild—and perhaps with as profound a meaning as the sound of bells in a Christian country.
In this extract he essentially acknowledges that the sound of the drums may be just as significant in the lives of the natives as the sound of bells would be for a native in a supposedly civilized country. It is ironic that only he can come to this conclusion and essentially save himself from moral turpitude whilst others, such as Kurtz, never do and are overwhelmed by their depravity.
On a more literal level, the drums attest to the presence of a primitive people not yet under the control of "civilization." As they 'speak their own language,' so they also live by their own rules.
Even so, their vulnerability to the white man's influence and conviction of his natural superiority eventually lead them into a deeper degree of barbarism than they have ever known before.
On a more symbolic level, the drums symbolise the savage instinct in all men which can run rampart in absence of imposed controls or sanctions:
Kurtz's appalling moral corruption is the result not only of external forces such as the isolation and loneliness imposed by the jungle, but also, Conrad suggests, of forces that lie within all men and await the chance to emerge. Kurtz perhaps realizes the depth of his own moral corruption when, as he lays dying, he utters "The horror! The horror!" Marlow feels this realization transferred to himself and understands that he too, living in a lawless state, is capable of sinking into the depths of moral corruption The savage nature of man is thus reached at the end of the journey, not upriver, but into his own soul.