In science there are six interlocking theories which are often referred to as fundamental to evolution:
#1 COSMIC: From the theorized Big Bang of (estimated) 14-20 billion years ago to the (evolution or) generation of hydrogen gas into existence.
#2 CHEMICAL: Gases (beyond hydrogen) and other higher elements evolving into existence. In other words, increasing molecular & chemical order and complexity over time happening by itself.
#3 STAR & PLANETS: Gravity, angular momentum, magnetism, radiation, and other “accidentally existing” forces coalesce (or evolve) the molecules (from above) that evolved into existence all by themselves into subsequent proto-stars, then later (over lots and lots of theorized time; billions of years) into stars and planetary bodies.
#4 ORGANIC EVOLUTION: Life emerging from sterile non-life by believed automatic advanced chemical processes. This has also been called spontaneous generation or more recently abiogenesis. Life from non-life; again, all by itself; increasing complexity and at some point in time – generating successive replication all by itself. Scientists today are using tax dollars to employ advanced, state-of-the-art equipment under expensive, carefully controlled high-technology laboratory conditions but this still hasn’t succeeded in any way yet … trying so hard … all to show that life could happen accidentally, without much intelligence. (That being the case indeed.)
#5 MACRO-EVOLUTION: Kinds of life diverging and occasionally increasing in complexity through random processes down through time. The theory is that single-celled creatures gave rise to (possibly) multi-cellular marine organisms. Later fish evolved into amphibians, and then into reptiles which (possibly diverged and) evolved into the birds and mammals. Over the theorized millions of years the divergent complexity of life in nature has (apparently) increased in order, numbers and magnitude. Many of today’s textbooks show lots of artistic illustrations of such beliefs.
#6 MICRO-EVOLUTION: Structured changes within pre-existing kinds of life. Heredity & Variation. This one is scientific and is observable in nature.
It is important to keep all of these various definitions in mind. Perhaps One but not all are true and verifiable? Perhaps others never happened at all? Just because it can be demonstrated that the fur length of offspring (Evolution #6) may vary per individual, this does not automatically mean that (Evolution #2) molecular chemical combination’s get more complex all by themselves. This belief has not been observed here on Earth at any time; creationists (who agree with Evolution #6) would be skeptical at swallowing belief in Evolution #2 without some kind of testable-repeatable evidence. It would be nice (for example) to send an oil tanker through an Antarctic storm and end up with a giant chocolate shake, but this has never been observed.