The Lost World is unified by the themes of discovery and reward. It is a noteworthy adventure novel because these themes are worked out in depth. Discovery is not only a theme but a literary technique in the novel. Ostensibly, the expedition to the jungles of Brazil is undertaken for the purpose of discovering unknown locales and animal life. However, the true motive of each of the explorers is more personal. Challenger's reward would be fame and the shaming of his detractors. Malone hopes to win the hand in marriage of Gladys Hungerton. Lord John Roxton is in quest of "masculine virility." And Professor Summerlee hopes to prove that "Professor Challenger is an absolute fraud."

Only Professor Challenger finds what he wants. He is so determined to have his way that he gives the impression that he would have built his own dinosaurs had he not found them. Malone's discoveries are more unexpected. He finds courage in himself, and his loss of Gladys emphasizes that his true reward is greater knowledge of himself.

But if prehistoric life existed upon the plateau, it was not superabundant, for we had no further glimpse of it during the next three days.
Another theme that underlies the experiences in The Lost World is that of evolution by natural selection. Dinosaurs and other ancient beasts survive on the plateau because they have been cut off for eons from the evolving life in the rain forests below. While they are in The Lost World, the explorers see the process of natural selection in action. On one end of the oval plateau live forest natives; on the other live "ape-men." In a cataclysmic struggle, modern humans—the natives—slaughter the animalistic ape-men, replaying a struggle completed eons earlier throughout the rest of the world.

In The Lost World, science is boldly advancing civilization and extending knowledge. Professor George Edward Challenger—daring, rude, and athletic— represents the arrogance of scientists who believe that science will end ignorance. Throughout The Lost World, Conan Doyle satirizes the self-assured belief that scientists are noble men seeking out nature's truths. For instance, when Challenger and Edward Dunn Malone—a journalist and the novel's narrator—first meet, they brawl:

We did a Catherine wheel together down the passage. Somehow we gathered up a chair upon our way, and bounded on with it towards the street. My mouth was full of his beard, our arms were locked, our bodies intertwined, and that infernal chair radiated its legs all round us.

The brilliant Professor Challenger loves a good fight, and thus he and Malone become companions in the hunt for The Lost World.

Searching the jungles of Brazil for a land of dinosaurs would seem to be serious business. Danger lurks at every step, yet Challenger, Malone, and their companions constantly bicker and slight one another. Challenger arrogantly brags about his discoveries, substituting showmanship for learned discussion. However, his scientific colleagues are so closed-minded and antagonistic that Challenger's arrogance is needed to get their attention. Throughout The Lost World, humor points out that even scientists resist discoveries that shake their comfortable beliefs.

Conan Doyle asserted that Professor Challenger was his favorite among his many characters. He may have liked Challenger's unending optimism and bold spirit, but he may also have been indicating his annoyance with the sometimes dominating role Sherlock Holmes played in his life.

The character of Challenger is less well developed and complex than Sherlock Holmes. Challenger is an "overpowering personality": "His head was enormous . . . He had the face and beard which I associate with an Assyrian bull; the former florid, the latter so black as to have a suspicion of blue, spade-shaped and rippling down his chest. . . . The eyes were blue-grey." Challenger is huge and muscular, and he always speaks with a "bellowing, roaring, rumbling voice." He is unchanging—always loud, always pugnacious, and always confident. Gifted with a brilliant intellect, he is impatient with others of lesser brilliance.

Conan Doyle asserted that Professor Challenger was his favorite among his many characters. He may have liked Challenger's unending optimism and bold spirit, but he may also have been indicating his annoyance with the sometimes dominating role Sherlock Holmes played in his life. Challenger is not nearly as well developed as Holmes, and he is not as complex. He is an "overpowering personality": "His head was enormous , . . He had the face and beard which I associate with an Assyrian bull; the former florid, the latter so black as to have a suspicion of blue, spade-shaped and rippling down over his chest . . . The eyes were blue-grey." Challenger is huge and muscular, and he always speaks with a "bellowing, roaring, rumbling voice." He is unchanging — always loud, always pugnacious, and always confident. Gifted with a brilliant intellect, he is impatient with others of lesser brilliance.