One big difference is that human characters in early science fiction were usually portrayed as having a moral compass, although it could be a very flawed one. They were making decisions about how to use new technologies, like in H.G. Wells' 'The Time Machine'. The human time traveler had to decide how to interact with the different races he encountered in the future. Animals, when they had significant roles, were often used to represent the 'other'. They were not part of the human moral framework in the same way. They could be a force of nature that humans had to either overcome or co - exist with, such as the giant squid in some sea - adventure - themed early science fiction.
Well, human characters in early science fiction were typically the ones driving the plot forward through their inventions and ideas. They were the scientists, the explorers. Take Jules Verne's works. His human characters were always on these grand adventures, exploring the unknown. Animals, on the other hand, were either companions or menaces. In some stories, like 'The Island of Doctor Moreau', animals were the subjects of cruel experiments, which showed how early science fiction used them to explore ethical questions regarding human interference with nature.
In early science fiction, human characters often had the ability to reason on a complex level. For example, in 'Frankenstein', the human creator was driven by his scientific curiosity and a sense of overreaching ambition. In contrast, animal characters, when they were more than just simple beasts, were usually depicted as having more instinct - driven behaviors. They might be seen as a source of mystery or a symbol of the wild and untamed. For instance, in some early sci - fi stories involving werewolves, the transformation into an animal - like state brought out a more primal side of human nature.