Most of us are aware that environment plays a role in shaping our biology. A few scars here and there, a creaky joint or two bear witness to environmental influences on biology. What is less commonly known is how powerful and far reaching many other environmental conditions are in shaping our biology. These influences extend to such things as our how we form social relationships, our capacity for intelligence and our ability to experience empathy. While we typically recognize the powerful influence of nature on our biological makeup, the role of nurture is often underestimated.
In simple terms, the nature and nurture aspects of biology are genetics and epigenetics. To view these formative aspects of our biology through a lens that renders some higher clarity we can view genetics, or DNA, like a collection of songs. It serves as the template for what is biologically possible. Epigenetics is like a song player. Epigenetics consists of many molecular sensors that trigger whether and when particular aspects of DNA are activated. Collectively these molecular sensors are known as the epigenome. While DNA is a huge factor in what is biologically possible, epigenetics largely determines when and how much the DNA “songs” within our genome are played. Our epigenome is connected to all the other aspects of our biology such as the machinery that swims around inside our cell membranes and how many and what type of receptors are present on the surface of cells that perceive and trigger internal responses to the external environment. These epigenetic sensory extensions in humans extend outward from our DNA to such concentrated sensory arrangement structures such as the eyes, ears, nose, tongue and skin. These larger sensory organs work in concert to perceive and relay this context of perceptions back through the individual cells to our epigenome. The epigenome can be viewed as the last communicative step in this process which can then respond by activating or deactivating specific portions of our genes.
Environmental conditions such as the broad cultural climate, localized social relationships and climate conditions are part of the process that shapes whether and when certain aspects of our DNA get expressed or not and how much. In other words; the vast extended epigenetic perception sleeve permeating and extending outward from our DNA turns on and off certain genes. Part of this process is to build and maintain our basic biological frame and the other part is to fine tune our biology to navigate what it perceives as the current environment.
Epigenetics and all the extended sensory elements of biology connected to it have an especially powerful influence on the way our biological body develops to maturity. It is particularly influential in our physiological development. The same way the choice of materials and building practices in the foundation of a building has a far reaching impact on the finished product; environmental influences in the early stages of biological development have lasting effects on our biology. Along with controlling the expression of DNA on what to produce in order to become a heart cell vs. a brain cell, epigenetics can influence what diseases we may be prone to and may be a direct factor of disease in some cases. In fact, there is some research that suggests that many forms of cancer in humans have a stronger link to epigenetic origins than to DNA mutations. Epigenetics can be considered in a very deep respect, the capacity we have to perceive and respond throughout our biology.
When we begin to understand the deeper implications of the relationship between the environment and our biology, we can see that notions like identity, free-will choice and self-awareness are much harder to accurately understand than many of our cultural assumptions have led us to believe. The effects of epigenetics encompass far more than what we think of as the physical aspects of biology, it affects our capacity to perceive and respond in general, including what and how we think, whether or not we can form solid pair bonded relationships, familial and tribal relationships and our general temperament among other things.
One example of lasting effects of epigenetic influence has been directly tied to social influences during infancy in mammals. Kittens and monkeys deprived of sight during early development become permanently blind. Some rat mothers spend more time licking, grooming and nursing their pups than others. Highly nurtured pups by comparison grow up with much calmer dispositions, while those that receive less to grow up to be anxious and otherwise stressed. This appears to be the case in all mammals, including humans. Early developmental environments can make a critical difference in whether our biology is shaped with a high stress cocktail of hormones and receptors or a more calm and self-assured one. It also influences what we are capable of seeing and not seeing. This environmental influence extends to the physical structure of our brain and the chemical cocktail inside our entire body that forms the basis of our identity as well.
The dramatic environmental influences during early development are because our biology searches for environmental queues to understand and adapt to the specific nature of the world in which it will exist. This search for environmental queues extends to individual cells and to our body as a whole. These queues can be picked up in the womb through chemical signals transferred from the mother, or postnatally through a wide variety of sensory signals. The biological direction our physiology is shaped by genes (nature), but it also shaped by our relationship to the environment (nurture). Our specific physiology and personality comes from a broad range of epigenetic influences that give expression to DNA. In other words; some DNA songs can get more air play than others.
One example of this genetic epigenetic relationship is revealed when we are exposed to environmental stress queues in our early development. Stress queues in our developmental environment trigger our biology to devote more developmental energy to constructing elements of reflexive anatomy, stress receptors and hormone production mechanisms among other things. Our developmental biology also sacrifices such things as cognitive intelligence to better adapt to what it perceives as the necessity for a more reactionary existence. Severe environmental stressors such as social deprivation in institutionalized infants results in reduced head size and overall physical growth. It also diminishes the capacity for emotional and social responsiveness, causes attention issues, and diminishes cognitive development and can lead to issues such as depression. These developmental influences on biology within us as individuals have enormous implications on how we relate to ourselves and in the context of society at large.
Other examples of epigenetic influence include behaviors such as those of us who do not maintain solid pair bonded relationships, but instead have multiple partners. This behavioral tendency is cultivated by epigenetic means. Those of us with “short tempers” or distant isolated personalities are often biologically queued to operate this way by environmental factors that happened long before we became aware in any verbal sense. This means that our verbal identity (who we think we are and what we think in general) develops in the context of biology that is far more powerfully shaped by environmental factors.
Because our verbal state of awareness is largely a reactionary consequence of environmental circumstances many of us have a biochemical makeup that is simply insufficient to develop an accurate sense of self-awareness without correcting for the cognitive filters that come with environmental factors. Without enough insight into the deep biological foundations of our identity, our verbal state of awareness is disconnected from the largest portion of the silent behavioral motivators that drive most of our experience of life. We become in effect, blind navigators with a persistent illusion of self-awareness. In this case, the circumstances and relationships we cultivate will be a result of influences that are not based on real choice even though we may believe the contrary. In actuality our lives will be more like that of a billiard ball moving solely according to happenstances outside the view of our illusory state of self-awareness – zombies, unable to transcend the stripes of happenstance because we do not even know that we do not know our true selves.
 A third leg of the influences on our biological makeup is chance. An example of this happens at a cellular level due to Brownian motion (also called paresis) which can randomly distribute cellular organelles at the point of cytokinesis. (When a cell divides into two) These organelles can have structural variables that can affect the function of the divided cells differently.
 The development and maintenance of biological organisms is affected by many types of chemical reactions that can switch parts of the genome off and on at strategic times and locations. Epigenetics studies these reactions and the various factors that influence them.
 DNA stands for Deoxyribonucleic acid which is a chemical instruction manual for biological organisms.
 For a greater view of this music perspective of biology read “The Music of Life: Biology Beyond Genes” by Denis Noble
 DNA can also have some effects on self-expression such as what is known as the Alu sequence (Arthrobacter luteus) which is thought to have a role in regulating gene expression, but this is in concert with an external RNA signal recognition particle known as 7SL, 6S, ffs, or 4.5S RNA. There may be instances where certain aspects of gene expression are self-regulated, but for practical purposes, elements external to DNA that have an impact on gene expression are treated here as being epigenetic in nature.
 Inside of cells are molecular machines called organelles that have specific functions. Sometimes they have their own membrane like the cell itself does. For instance; mitochondria are organelles within human cells that have their own DNA and epigenetic features.
 Cell receptors are specialized proteins that pierce the cell membrane (skin) and are specifically shaped to receive certain molecular shapes flowing through the fluids outside the membrane. Insulin receptors are an example of this communication process broadly called cell signaling. In human biology signaling molecules include hormones, neurotransmitters, cytokines, growth factors and cell recognition molecules. These molecules attach to receptors and trigger certain activities within the cell depending on what they are. (called signal transduction)
 This description is meant to illustrate the general theme of the relational dynamic between the genome and the epigenome. It is not meant as a hard and fast rule that applies in every case all the time.
 Environmental influences that affect physiological structure have maximum influence during the stages when those developmental processes are under way. These key developmental periods are sometimes called “critical” or “sensitive” periods because of their importance in shaping development and because they are more sensitive to environmental influences compared to other stages of life.
 See “Epigenetic influence and disease” by Danielle Simmons, Ph.D. http://www.nature.com/scitable/topicpage/epigenetic-influences-and-disease-895
 See “The postnatal development of the visual cortex and the influence of environment” Nobel Lecture, 8 December 1981 by Torsten N. Wiesel
 Cortisol and norepinephrine are examples of stress hormones, but there are many other factors that shape our biological disposition to stress. The number and location of receptors in the body as well as diet and other factors can contribute to the overall biological disposition to stress.
 For more information read “The caregiving context in institution-reared and family-reared infants and toddlers in Romania” by AT Smyke, SF Koga, DE Johnson, NA Fox, PJ Marshall, CA Nelson, CH Zeanah. Journal of Child Psychology and Psychiatry. 2007; 48(2):210–218. Also read “Early childhood adversity and adolescent depression: the mediating role of continued stress” by N. A. Hazel, C. Hammen, P. A. Brennan and J. Najman.
 For more information read “The Neurobiology of Pair Bonding” by Larry J. Young and Zuoxin Wang