How living things get to be what they are is a question that has occupied philosophers and scientists for a very long time.  In the past two or three hundred years, the focus has been on what Gregor Mendel has called units of heredity, or the physical elements that are transmitted from parents to offspring.  These are now called genes, and have become an integral part of the conversation about human beings and their health. 

The cells of living beings contain chromosomes, which are recognized as the bearers of inheritable information.  Chromosomes contain a double helix of DNA (deoxyribonucleic acid) and protein.  DNA  is a long series of units called nucleotides.  It is believed that DNA makes RNA (ribonucleic acid), which differs from DNA in chemical composition.  RNA translates the information coded in the DNA and prompts the specific development of various proteins in the body.  

Genes are stretches of DNA on the chromosome, and they may be thousands of nucleotide units in length.  Gene splicing, or genetic engineering, consists of snipping one (or more) genes out of the DNA of one organism and splicing it into the DNA of another organism, much like film or sound tapes are spliced to re-arrange the sequence of images or sound.

Individual genes provide codes for the many thousands of proteins, including enzymes, that are found in the human body.  The theory called the central dogma of molecular biology is as follows: DNA makes RNA makes protein in a one-way, irreversible sequence, and no reverse feedback is possible -- that is, the environment cannot influence the DNA, and acquired characteristics are not heritable.^21(p104) The genotype is the total inheritable genetic line of a class of organism (e.g., A sheep), while the phenotype is the individual expression of those genes in a single organism (e.g., a particular lamb).

The chromosome theory of inheritance includes the following:

1. The collection of chromosomes in the fertilized egg constitutes the complete set of instructions for determining the timing and details of the formation of all the organs and tissues
    

2. DNA is self-replicating
    

3. DNA does not adapt to environmental stimuli
    

4. DNA is the generator of the structure that emerges from the fertilized egg in sexual reproduction.

The reductionism of genetics was firmly established with the work of Richard Dawkins, whose concept of the selfish gene proposed that organisms are nothing but the way in which genes reproduce.

Brian Goodwin, a British biologist and author of How the Leopard Changed its Spots: The Evolution of Complexity, is one of a number of scientists less than enamored with the gene/chromosome theory of inheritance.  I will paraphrase his objections to the list enumerated in the previous section.

1. This proposition is incorrect.  Genetic instructions, which create proteins, are insufficient to explain the processes that lead to the various organ formations such as those of the heart, nervous system, or limbs.  Genes are not sufficient to explain the morphology of the organism.
    
2. DNA is not an independent replicator; it can only replicate accurately within the context of the cell in which it resides.  That is, it needs a supportive environment, including an energy source and enzymes to help in the replication process.   This means that the whole unit reproduces, not the DNA by itself.
    
3. There is ample evidence that yeasts and bacteria can change their DNA in response to environmental information.
    
4. DNA stabilizes the morphology of the organism, but does not generate it by itself.

In addition, while a particular gene defect might be associated with a particular disease, it cannot predict if, when, and how that disease will manifest itself.  

Genetic engineering, which is the splicing of genes from one organism into the germ cells of another, for all its magical promises, is a literal Pandora Box.   There are serious concerns about the irreversible effect that genetically modified organisms such as corn and soy might have on the ecosystem and its life forms, because these changes in genetic material are inheritable as well as laterally, (or horizontally) transmissible via pollen, insects, and wind-borne DNA particles. Cloning, a procedure that allows the development of new individuals from individual cells of adult animals, instead of by normal egg and sperm union, theoretically should produce animals identical to the parent donor of the cells; however, many cloned embryos die before birth and the survivors often have growth abnormalities such as breathing difficulties, heart problems, and gross overweight.

Genetics is quickly becoming the new religion, and proposes to explain everything from breast cancer to personality trains as stemming from the simple action of genes.  There is a danger here.  As Ruth Hubbard and Elijah Wald argue in Exploding the Gene Myth: How genetic information is produced and manipulated by scientists, physicians, employers, insurance companies, educators, and law enforcers, The myth of the all-powerful gene is based on flawed science that discounts the environmental context in which we and our genes exist.  It has many dangers, as it can lead to genetic discrimination and hazardous medical manipulations.      

Bruce Lipton, Ph.D., a former cell biologist and professor, in his book The Biology of Belief:  Unleashing the Power of Consciousness, Matter and Miracles (Hay House:  2005), clearly shows that genes are totally at the mercy of their environment – having a gene related to a disease does not in the least predict that one will get such a disease.  (By the way, everyone should read this book about mind-body medicine!)  This new understanding about the important influence of the environment is called “epigenetics.”

According to the Wall Street Journal (1/ 9/2010), the progression of coronary heart disease, diabetes, hypertension, prostate cancer, obesity, and other chronic conditions have been reversed with integrative medicine approaches such as plant-based diets, yoga, meditation and psychosocial support.  These approaches may change the expression of hundreds of genes in only a few months. Genes associated with cancer, heart disease and inflammation were downregulated  ("turned off") whereas protective genes were upregulated ("turned on.") Even drugs have not been shown to do this.

Mae-Wan Ho, Genetic Engineering:  Dream or Nightmare? (New York: Continuum, 1999).

Richard Dawkins, The Selfish Gene (Oxford, UK: Oxford University Press, 1976).

Brian Goodwin, How the Leopard Changed Its Spots:  The evolution of complexity (New York: Charles Scribner's Sons, 1994).

Ruth Hubbard and Elijah Wald, Exploding the Gene Myth:  How genetic information is produced and manipulated by scientists, physicians, employers, insurance companies, educators, and law enforcers (Boston, MA: Beacon Press, 1999).

David Humphreys and others, AEpigenetic Instability in ES Cells and Cloned Mice,@ Science 293, no. 5527  (July  6) (2001): 95-97.

Evelyn Fox Keller, Refiguring Life:  metaphors of Twentieth-Century biology (New York: Columbia University Press, 1995).

MF Lee and others, ATotal intestinal lactase and sucrase activities are reduced in aged rats,@ The Journal of Nutrition 127, no. 7 (July) (1997): 1382-7.

Mark E. Lowe, AMolecular mechanisms of rat and human pancreatic triglyceride lipase,@ Journal of Nutrition 127, no. 4  (April) (1997): 549-57.

Dolinoy, D.C., et al., Maternal genistein alters coat color and protects Avy mouse offspring from obesity by modifying the fetal epigenome. Environ Health Perspect, 2006. 114(4): p. 567-72.