Initially, Marlow doesn't really think much about indigenous Africans. He's going to the Congo for purely selfish reasons—to make money exploiting the natives—so he doesn't regard them as anything more than a cash cow. There's a lot of money to be made out in the so-called Dark Continent exploring Africans, and Marlow's determined to grab his share.

After arriving in Africa, however, Marlow starts to see Africans in a completely different light. Wherever he looks, he cannot help but notice that the indigenous people are chained and enslaved, treated like animals by their colonial overlords. Though it's unlikely that Marlow has suddenly been converted into a firm believer in racial equality, he does at least see the native Africans as human beings rather than objects to be exploited, which is how most of his fellow colonialists see them.

In one particularly striking passage, Marlow is struck by an unforgettable sight as he travels up the Congo. As he sees some African men paddling, he notices from a distance "the white of their eyeballs glistening." This indicates that Marlow is able to see beneath their skin to behold their inner humanity—something that sets him apart from the common run of white European colonialists.

In Joseph Conrad's Heart of Darkness, Marlow's character sees the natives as a race of people who are being exploited by the white race.

When King Leopold II of Belgium established a colony in the African Congo, he proclaimed it was for humanitarian reasons—he wanted to enlighten the natives. While there was mention of bringing Christianity to them—and he even allowed Protestant missionaries to travel and live in the Congo—Leopold was motivated only by sheer greed.

When Marlow travels into the Congo, the Company has hired him to retrieve Kurtz, one of their best agents in securing ivory—in fact, there is some jealousy expressed toward Kurtz by others because no one can compete with the amount of ivory he exports from the Inner Station.

For Marlow, this begins simply as an assignment. He has never traveled to this part of the world before. Though there is some foreshadowing by the captain that takes Marlow to the Lower Station, nothing could prepare him for the way the white men are treating the indigenous people of what was then called the Congo.

Revulsion grows within him over the white man's dehumanizing colonization of the Congo. 

Marlow hears the natives described by the whites as "enemies" and "criminals," but he sees men who have been enslaved. They walk like they are zombies—even though their bodies live, their spirits are dead. Marlow is horrified. The men are "...connected together with a chain..." Their eyes "...stare stonily..." They walk past Marlow "with that complete, deathlike indifference..."

Marlow leaves the sight of the chain gang behind, trying to put them out of his mind. We can infer in the reading that he is struggling to maintain a semblance of self-control.

You know I am not particularly tender; I've had to strike and to fend off. I've had to resist and to attack sometimes—that's only one way of resisting—without counting the exact cost, according to the demands of such sort of life as I had blundered into. I've seen the devil of violence, and the devil of greed, and the devil of hot desire; but, by all the stars! these were strong, lusty, red-eyed devils, that swayed and drove men—men, I tell you.

This passage reveals that Marlow is struggling to maintain his composure in circumstances that make no sense. When he sees men...

...scattered in every pose of contorted collapse, as in some picture of massacre or pestilence...I stood horror-struck...

Marlow is not an innocent, untried youth. He has had to face hard times in his life, fighting "devils" of many kinds. This experience, however, has taken its toll.

Marlow cannot look at the natives as the violent Europeans do; he cannot abide how atrociously they are treated. Marlow does not see them as criminals, or lesser creatures. He recognizes not only that they are men, but that those who are driving them—enslaving them—are demons: "red-eyed devils."

Marlow's job is to bring Kurtz back. Had he needed the help of the natives, there is nothing to indicate that he would have treated them badly. Because Marlow is a man of some moral standing (demonstrated by his reaction), the treatment of the natives affects him deeply. This foreshadows the horror that still awaits him on the remainder of his journey. Unlike the Company men, the natives are not a means to Marlow's success or material wealth. They are flesh and blood as he is. And he is mortified not just by seeing what is happening to them, but in realizing there is little he can do about it.

In Joseph Conrad's Heart of Darkness, examine Marlow’s attitude toward the Africans. Is there any evidence that he is condescending toward them? Support with examples.

In Joseph Conrad's Heart of Darkness, I do not find any sense that Marlow is condescending toward the Africans. If anything, he is appalled at how the Europeans treat the natives. If he has difficulty with anyone, it is with the agents of the Company who see themselves as a vastly superior race, while exhibiting a total disregard for the population they have enslaved.

Marlow has been delivered into a part of the world where...

A prevalent feeling among Europeans...was that the African peoples required introduction to European culture and technology in order to become more evolved. 

"Someone had to do it," was the attitude, and the term "white man's burden" shows just how superior Europeans saw themselves by comparison to the indigenous people of the Congo. King Leopold II of Belgium decided there was great wealth to be had in Africa—so he established a colony there, and his agents "raped" the land and its people.

Marlow is new to this part of the world, but it does not take long for him be horrified by what he sees:

Revulsion grows within him over the white man's dehumanizing colonization of the Congo.

Marlow witnesses the treatment of enslaved men, chained like animals...

Six black men advanced in a file, toiling up the path...I could see every rib, the joints of their limbs were like knots in a rope; each had an iron collar on his neck...

Nearby, Marlow finds another group of men. Some, he feels, have come to this spot simply to die. While the Europeans act as if the natives are a threat. Marlow sees none of this, and he is repulsed by how they are abused:

They were dying slowly—it was very clear. They were not enemies, they were not criminals, they were nothing earthly now—nothing but black shadows of disease and starvation...[They were] scattered in every pose of contorted collapse, as in some picture of massacre or pestilence...I stood horror-struck...

When one man is blamed for the fire in a small shed, he is brutally punished.

The shed was already a heap of embers glowing fiercely. A n***r was being beaten near by. They said he had caused the fire in some way...he was screeching most horribly. 

Marlow's descriptions of how the natives are treated share only his horror and pain in watching "men" (for he sees them as men and nothing less) brutalized so casually by the Europeans.

It is for the Company's agents that Marlow seems to experience a sense of condescension. When the brickmaker begins to dig for information, Marlow is confused—then amazed...the man cares only for his own position with the Company, and how Kurtz and now Marlow (he thinks) have threatened that.

Marlow watches the pilgrims (agents) fire with wild abandon into the jungle simply to kill unseen natives. And another point, Marlow blows the steamboat whistle to frighten the "savages" away from danger:

I pulled the string of the whistle, and I did this because I saw the pilgrims on the deck getting out their rifles with an air of anticipating a jolly lark. At the sudden screech there was a movement of abject terror through that wedged mass of bodies. 'Don't! don't frighten them away,' cried someone on deck disconsolately. I pulled the string time after time.

Marlow suffers to see how the natives are treated. His disgust is directed at the Company men and their disregard for human life.