Obviously there will always be a slight bias in one direction or another when the niche is changing. And obviously niches are always changing, but to extrapolate this obvious truism into the nature of change in species with no evidence or experiment to support it is a massive leap. We only observe species changing at bottlenecks. Selective breeding is the imposition of such artificial bottlenecks in a systematic way. Nature does it exactly the same way with natural bottlenecks but this is hidden by the fact that so much change, especially minor changes that can have huge effect, are caused by mutation rather than bottlenecks. There is no "Evolution" and no "survival of the fittest" except in the minds of most homo omnisciencis.
The better way to examine species is with entropy. Entropy is considered a state variable, meaning any given state of matter is defined by a constant entropy. Water at 25C and 1 atmosphere has an entropy constant of 188.8 J/K-mole. At the nano-scale, a lot is going on in the water; quantum mechanics, but this all adds to a constant entropy value at the macro-level.
Each species define a material state of fixed entropy. These states appear to be quantized, with gaps between species states. It will take more than a single positive mutation to jump to a higher or new species state. The better model for change is like a mixing pot, until there is sufficient integrated change, for the next quantum step upward; higher entropy or new species state. Distinct species cannot reproduce with other species since each has a unique DNA state.
Entropy is also connected to complexity, induced within each state, with humans adding complexity, even to nature and the earth, beyond any other species on earth. Species are complexity generators, adding entropy; new states of technology.
Say we have a mutation on the DNA. This is then transcribed into mRNA, and then translated into protein. The water then takes the protein and folds and packs it to minimize its surface tension. It then is placed in its equilibrium spot. If it does not fit in, it goes to recycle. If does fit in, it becomes part of the mixing pot, until enough changes occur for a new quantum species state.
Most of the DNA is noncoding. These are called junk genes, but are anything but junk. The preponderance of junk genes on the DNA suggest that most mutations are not coded, but are connected to the junk genes. These changes have impact on the configurational potential of the entire DNA, which may play more of a role for defining a species.
This is similar to an enzyme, that has a surface active site, but is composed of a longer balled up protein structure, that is all necessary, for the enzyme expression. The junk genes sort of stay balled up, since they are not coded to make mRNA, but their presence allows the coded genes to work and become active. There is not much difference between species when it comes to coding genes, with noncoding the majority and the wild card for a species DNA entropy constant. If the noncoding genes are changing, it may not appear we are add anything new; new function, but still this can alter the expression of what is already there, until you can't breed with another or previous species.