The Gene – An Intimate History (2/2)

This post follows on the heels of an earlier post this morning. As noted at the end of that post, about half of the sticky tabs I stuck throughout the book deal with a particular interest of mine and that’s what this post covers. What we consider as normal and not normal in terms of our physical, biological, and cognitive lives is determined in large part by how we choose to frame the definitions. 

As the 1800s was turning into the 1900s, the English doctor Archibald Garrod “had conceptually visualized a human gene and explained human variation as ‘chemical diversities’ encoded by units of inheritance. Genes make us human, Garrod had reasoned. And mutations make us different.” [bold face my addition] Garrod’s work set off “a systematic effort to create a catalog of genetic diseases in humans” and, oh my, there is an astonishing array of such diseases. Penetrance refers to the fact that “even if a mutation was present in the genome” of a person, “its capacity to penetrate into a physical or morphological feature was not always complete.” 

I am intrigued by Mukherjee’s further elaboration on these ideas as he takes us through a growing definition of disease.

The definition of disease rests, rather, on the specific disabilities caused by an incongruity between an individual’s genetic endowment and his or her current environment–between a mutation, the circumstances of a person’s existence, and his or her goals for survival or success. It is not mutation that ultimately causes disease, but mismatch. (p 264)

Even the nature of the “mismatch” is mutable: since the environment is constantly subject to change, the definition of disease has to change with it.”

…the lack of fitness–illness, in colloquial terms–was defined by the relative mismatch between an organism and environment. (p 265)

Over and over I was struck by the normalcy of differentiation among humans. It turns out that “facial features and heights are shared because genetic variations are shared among individuals,” meaning within families. Stop for a moment to consider what humanity would be like if we all looked the same with the same physical traits. How would we know who was who? And what traits would be the ones that we all had? Surely there is already a sci fi book with such a pretense. (If you know of one, please list it in a comment so I can borrow a copy from the library. Thanks!)

The natural segue is to move from pondering physical differences to intellectual differences and the influence of environment. More vocabulary words emerge from this discussion: heritable, which is a trait influenced by genes, and inheritable, which is a trait that is handed down intact from one generation to the next. (p 346) 

Using the example of growing a tall and short plant in various conditions (insufficient nourishment and appropriate nourishment), both plants grow short without the necessary nutrients, while both plants grow to their natural height with adequate nourishment, meaning the short plant grows to a short height and the tall plant grows to its tall height. Mukherjee states that

Whether genes or environment–nature or nurture– dominates in influence depends on context. When environments are constraining, they exert a disproportionate influence. When the constraints are removed, genes become ascendant. (p 347)

This is an important idea to him, and he asterisks it to a footnote on the page: There can hardly be a more cogent genetic argument for equality. It is impossible to ascertain any human’s genetic potential without first equalizing environments. [italics my addition]

There is much food for thought in this book. It is filled with a history of the discovery and science of genes, diving deep into DNA and spiraling back out to try to discern what it means to be human. I am very much in synch with Mukherjee’s thoughts about equalizing environments and think about this in the context of 38 years of teaching, 36 years of parenting, and over 60 years of living in a world consisting of beautifully diverse humans!

I leave with this image of the circular flow (p 410) of biological information, the final flow that began as a few statements many pages earlier in the text (and was noted in my previous post).circular flow

 

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