Give a single example. Then we can talk.
Well more than just one...
Basic evolution: a small number of more or less "random" DNA mutations are observed in every offspring of every species.
Most are harmless and serve really only to help us track our ancestry through passed-down harmless mutations.
Of those which have some affect, most are harmful and often get acted on by natural selection.
But a very small percentage can be helpful and those can accumulate over many generations leading to speciation.
That's evolution in a nutshell.
So speciation can be observed at every step of the way, from simple short-term adaptations which create, for example, new breeds & varieties, to much more significant & long-term changes creating sub-species, species & even genera.
An example of one mankind forced & witnessed from the beginning, is the creation of dogs as a species separate from wolves.
Another example illustrating degrees of biological separation are polar bears & brown bears, once classified as separate genera in the Ursidae family, now discovered to be simply two species in the genus Ursus.
Point is: evidence clearly shows increasing degrees of biological separation -- evolution -- on a continuum from mere breeds through species, genera, family, class etc.
And fossil records reveal these degrees of separation take longer times (millions of years) the greater the separations.
So mankind has been around just long enough to create a separate species from wolves, dogs, but not yet long enough to have witnessed, say, the separation of Indian elephants as a distinct genus from African elephants.
However, evidence of it is all around us, from the fossil record to comparisons of their DNAs.
Is that a good enough start for you?