Charles Darwin was an outside-of-the-box thinker during his time, and questioned what we really knew back then about evolution and the origin of our species. He made his first discovery in Argentina, which would turn out to be a very influential discovery. He discovered that certains kinds of finches and tortoises on the Galapagos Islands differed in certain characteristics, depending on which island they lived upon.
As he came to the conclusion that although these birds and tortoises were the same, the species had adapted to suit whichever island they lived on. He also studied dog breeders, and how the best specific traits from both parents were passed down. This is called natural selection, and the pattern was that the creatures that survived were the best suited to the environment they lived in. Each generation would have varied characteristics, that would allow the fit to remain fit and the less fit to die off or vanish. During his time on the islands, he managed to find enough research to publish the book, “On the Origin of Species,” . This book also shared his research and discoveries that not all DNA stayed the same. The genes that passed on would mutate, and result in genetic change. An excellent example of this would be whales. Whales still have vestigial organs, which are organs they were born with, but have no use for. Whales have hipbones in their bone structure, seeing as they use to roam on the land instead of water. Now, whales are completely adapted to the water environment, and have no use for hipbones anymore. 
This can help explain why the bones of the human ear developed from fish gills, and that prehistoric fish eventually evolved to provide us now with the genes for arms and legs. While humans have been distantly related from fish, humans shared a 1% difference in the DNA of humans and chimps. The differences in the DNA sequences were in the switch gene, which were in a gene that involved the brain. The brain is one of the signature human organs, and the other one is the hands/thumbs. 
In conclusion, Charles Darwin’s discovery and research put into DNA can help prove that humans did in fact evolve from fish, and knowing that, we can trace back the in-between stages of humans and fish. Today, we can understand that chimps and humans are very closely related, and we can’t help but wonder if the chimps will evolve to be able to preform some of the functions we also do.
Image 1 from Socratic.org
Image 2 from Owutranscript.com