Scientific Definitions
Nature
"Evolution is a process that results in changes in the genetic material of a population over time."
University of California Museum of Paleontology
"Biological evolution, simply put, is descent with inherited modification."
National Human Genome Research Institute
"Evolution, as related to genomics, refers to the process by which living organisms change over time through changes in the genome. Such evolutionary changes result from mutations that produce genomic variation, giving rise to individuals whose biological functions or physical traits are altered. Those individuals who are best at adapting to their surroundings leave behind more offspring than less well-adapted individuals. Thus, over successive generations (in some cases spanning millions of years), one species may evolve to take on divergent functions or physical characteristics or may even evolve into a different species."
Encyclopedia Britannica
"Evolution [is a] theory in biology postulating that the various types of plants, animals, and other living things on Earth have their origin in other preexisting types and that the distinguishable differences are due to modifications in successive generations."
BioLogos
"The theory of evolution states that all the lifeforms on earth share a common ancestor as a result of variation and selection over a very long time (currently thought to be around 4 billion years)."
National Academies
"Evolution consists of changes in the heritable traits of a population of organisms as successive generations replace one another. It is populations of organisms that evolve, not individual organisms."
Conclusion
As these definitions make clear, evolution is a unitary process operating at multiple scales. The scientific community is unanimous in recognizing that the mechanisms that drive small-scale changes (microevolution) are the same mechanisms that, over longer time periods, produce large-scale changes (macroevolution) including the origin of new species, genera, and higher taxonomic groups.
The distinction between microevolution and macroevolution is simply one of time scale and degree of change, not a difference in mechanism. Attempts to accept microevolution while rejecting macroevolution are inconsistent with the scientific understanding of evolutionary processes.