Darwin believed that all species originated with one species. He says that natural selection exists largely based on the belief that there is variation in nature, a struggle for existence, and competition. This leads to the variations diversifying into new groups and species, growing bigger and creating more species from those previous species. These slight variations get more extensive over time as the the species slowly changes. The amount of time life has existed is extremely lengthy and allows for those slight variations to eventually become a very different species. The amount of these in-between variations is so great and undiscovered that we likely won’t be able to uncover them to fill in the gaps.
I find Darwin’s thoughts mostly compelling. It makes sense to me that the slight variations of a species would expand larger and larger over time. However, beginning with a single species seems a bit like a stretch, as though he’s trying to expand the 7 days God created the Earth into millions of explainable years. Additionally, it doesn’t explain enough to encompass humans unique cognitive abilities. If it were simply due to the expanse of slight variations, why isn’t there another species with somewhat comparable cognitive structure or ability for innovation? What was the very beginning variation that sparked such a monumental quality?