Evolutionary health and fitness is a science-based methodology for increasing wellness using evidence derived from the study of human evolution.
Despite the fact that only around 16% of Americans believe that humans evolved over the course of a million years into their present state, the theory of evolution remains the cornerstone of modern biological science.  Much like how the Big Bang theory or the Continental Drift model are unifying ideas for the fields of cosmology and geology respectively, evolution is the central thesis through which all other biological concepts are compared against.
The renowned Russian geneticist Theodosius Dobzhansky said, “Nothing in biology makes sense except in the light of evolution.”
Why is evolution important for understanding the health of modern humans?
One of the basic tenets of evolutionary theory is that organisms inherit various traits, each of which may be beneficial or detrimental to the survival of the organism depending on prevailing conditions of its environment. If the traits are useful, the organism is more likely to reproduce and pass on those traits to its offspring. Assuming that the organism remains in the same environment, over time its offspring will become increasingly better adapted to surviving and attaining optimal health within that habitat.
Over several hundred thousand years, Homo sapiens became adapted to achieving optimal health in the various habitats that they lived in during the paleolithic era. While there was some variability due to different climates and food resources available, the robust and adaptive nature of the species allowed humans to spread over much of the world.
Despite this adaptability, there was still nutritional and physical preconditions which the paleolithic human body expected of its environment. These would be things like the prevalence of unprocessed food, abundance of complete proteins from meat, sporadic yet intense physical exertion, and generally active daytime lives.
One does not need to look very hard at the lives that most modern humans live to discover that we have strayed far from the expectations that our genome has of our environment. Indeed, many people might fail to achieve any of the items found in the list I just provided. In not doing so, one could say that modern humans experience something described as “phylogenetic maladjustment”. 
According to this principle, if the conditions of life of an animal deviate from those which prevailed in the environment in which the species evolved, the likelihood is that the animal will be less well suited to the new conditions than to those to which it has become genetically adapted through natural selection and consequently some signs of maladjustment may be anticipated.
Haven’t humans adapted to living in agriculture-based societies by now?
It is likely that some level of adaptation to agriculture has been happening since it’s inception, though the prevalence of “diseases of civilization” would suggest that humans have not fully adapted to this changed environment. Although some scientists like John Hawks contend that human evolution has accelerated following the conclusion of the paleolithic era , in general adaptation is a very long term process spanning hundreds of thousands of years, far more than the 10,000 years since humans changed to an agricultural lifestyle.
We can form this conclusion by examining the health of indigenous populations of hunter-gatherers which still persist, and observing that they exhibit remarkably high levels of health and adaptation to their environments. Further, as westernization continues, these same populations start to contract the same types of diseases which plague more developed societies, like obesity, diabetes, and heart disease.
How can we use this information to increase our health and wellness?
Using the information we know of our paleolithic ancestors and other various traditional cultures, we can reshape our modern lifestyle so that it mimics or facilitates the nutritional and physical expectations of our bodies. We can do this by experimenting with dietary models like the paleo diet, or with a natural movement oriented exercise program.
While it would be ludicrous to expect modern civilization to revert to a hunter-gatherer existence for the sake of good health, we can hope that advances in technology will afford us the ability to devote more time and effort towards recapturing some of our human evolutionary heritage.