Re-Envisioning Cell Theory (Part 1)

Now available for courses, From Cells to Organisms delves into the nature of scientific practice, showing that results are interpreted not only through the lens of a microscope, but also through the lens of particular ideas and prior philosophical convictions. In a new three-part blog series, author Sherrie L. Lyons will discuss her book and delve deeper into the history of cell theory. In part one, she examines the question: “What makes something alive?”

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Part 1

What is life? The world is in the midst of a pandemic that is wreaking havoc in every aspect of our lives, all caused by the virus SARS-CoV-2. Highly infectious, it has spread around the globe. But is a virus even alive? It can only reproduce itself by taking over the cell’s metabolic machinery. On its own, it can do nothing. From Cells to Organisms: Re-envisioning Cell Theory sets cell theory in the broader context of the most fundamental question of biological investigations: What makes something alive?

Our earliest ancestors believed that all objects were imbued with their own unique spirit whether it was a rock, a river, a cat, or a rose. Yet beginning with the Greeks, if not earlier, people began to think that there is something fundamentally different between a boulder and the mountain lion sitting on it. The lion is animated by some kind of vitalistic force. But what is the nature of this vital force that allows an egg to grow, differentiate, and mature into a lion, but leaves when he dies? Is this life force essentially the same for all living beings, and if so, how is it able to manifest itself in such different creatures – fish, flowers, trees, dogs, and humans? How is life maintained? What is the cause of such diversity, not only the variation between species, but within species? What is responsible for like producing like or, in modern-day parlance, what is the hereditary material and how is it transferred from generation to generation? It is going to take more than 2,000 years before these questions are answered in detail.

We now know that the basic unit of life is the cell and no vitalistic force is involved. Nevertheless, the most basic question – how does life differ from non-life? – still defies a complete explanation. Furthermore, in spite of being one of the great unifying theories for biology, cell theory has always had critics. Examining the reception and history of cell theory provides a wonderful opportunity to elucidate important themes and controversies in biology. In my book, I use Thomas Huxley’s (pictured below left) objections to illuminate problematic aspects of the theory, particularly in how it shaped embryological research.

Is the cell the smallest structural unit that can be considered alive and is it independent? A living organism is the product of all the interactions and activities of its constituent parts, but each of those parts has some attributes of what makes something “alive.” In addition, the cell becomes an organism by communicating with other cells within the organism. The organism is informing the cell, but at the same time the organism is also being informed and shaped by the environment. This challenges the idea that organisms are single genetic individuals and that the fundamental unit of an organism is the cell. The history of cell theory reveals that what constitutes this primary element has been a source of controversy, with various theories suggesting units that are either smaller or larger than the cell.

The spectacular success of genetic investigations culminated with the elucidation of the structure of DNA in 1953. We understand in great detail how it carries out its function as the hereditary material. This resulted in genetics dominating the thinking in understanding a variety of biological problems from evolution to cancer. However, real progress was made in understanding heredity by redefining and narrowing its meaning. Prior to the nineteenth century heredity and development were considered to be two aspects of the more fundamental problem of generation. Heredity came to mean transmission genetics, i.e. how the hereditary material was transferred from one generation to the next. Rather than being an essential component of embryological development, heredity came to be regarded as totally independent of development.

This history goes full circle and ends where it began with the problem of generation. Heredity and development are inextricably interconnected and the advances in understanding heredity owe much to its developmental origins. Written in 1853, Huxley’s ideas foreshadowed present day research that is reuniting heredity with development, integrating evolution with development and challenging traditional views of the cell. Development begins with a single cell and thus the history of cell theory provides a window to view the progress made in understanding this complex process. The history of development also shows that investigations in understanding the cell proceeded in two very different directions, revealing a tension between reductionism and a more holistic approach to understanding this fantastic phenomenon we call life.

Part Two and Three of this blog series will explore some of these controversies. From Cells to Organisms invites the reader to “re-envision cell theory.”

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Interested in finding out more about From Cells to Organisms? Click here to read an excerpt from the book.

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