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A small bundle of human nerve cells are being cultured in a petri dish. The cells divide. They differentiate into cell types found in the brain. The cell network grows dense and develops brain-like structures—layers and folds. The cells begin to signal. The brain cell cluster has been derived from skin cells harvested from science writer Philip Ball’s shoulder.

The scientists who created Ball’s skin-turned-brain organoid study brain development and want to understand the basis of neurodegeneration. But what exactly goes on inside these cell aggregates, and could we reach a point at which they are more “brain” than “brain-like”?


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All living things come from an egg, argued William Harvey (incorrectly) in 1651.




Biologists can also build embryo-like structures (embryoids) from human stem cells, which can be used to study early prenatal development. However, synthetic embryos can develop certain features—such as the primitive streak, a structure that establishes bilateral symmetry in an orga nism—that mark, for some, the transition from embryo to individual human being.

Ball’s experience grappling with how to think about these living structures, as documented in his new book, How to Grow a Human, is part of a larger question with which humanity has wrestled for centuries: What is life, and how might our understanding of it change with our ever-increasing capability to manipulate it?

The book offers a provocative, meandering take on the progression of groundbreaking biotechnological capabilities. For example, in chapter 3, Ball explores the dawn of tissue culture at the turn of the 20th century and the motivations of the scientists who conducted the research. Ross Harrison sought to settle a debate between Camillo Golgi and Santiago Ramón y Cajal over the makeup of nervous systems; the former argued that nervous systems were one uninterrupted structure, whereas the latter believed there to be distinct nerve cells. Along the way to showing that nerve fibers lengthen through nerve cell proliferation, confirming Ramón y Cajal’s hypothesis, Harrison was the first to develop a technique to keep tissues alive with active cell growth in vitro, sustaining amphibian embryonic tissue in jars.

Alexis Carrel, on the other hand, was a white supremacist striving to preserve “a ‘superior stock’ of humankind.” Carrel and his team iterated on and applied Harrison’s method to many different tissues, including those of birds, embryonic chickens, and, of course, humans. Here, Ball also works in how science fiction writing was influenced by early advances in cell biology, describing Julian Huxley’s “The Tissue-Culture King,” which centers on a biologist who redesigns members of a remote tribe and builds living objects of worship from the flesh of the tribe’s king. Although interesting, asides such as this disrupt the narrative’s continuity.

Ball’s writing is most absorbing when he reflects on boundary-pushing research, such as advances toward converting human skin cells to eggs or sperm or the promise of approaches for fabricating human organs to help people who need transplants. In chapter 5, for example, he describes experiments in which rat cells formed pancreases in mice, and others in which human cells survived in pig and cattle embryos, and then considers how governments and the public might approach the prospect of harvesting human organs grown in other animals.

Discussing how and where we have drawn ethical and legal lines for procedures such as in vitro fertilization and preimplantation genetic diagnosis (PGD) of embryos, Ball contemplates what historical precedent may mean for the governance of emerging biotechnological capabilities. Unlike in the United Kingdom, where PGD is permitted only to avoid implanting an embryo with a serious heritable disease, the United States does not regulate PGD-enabled embryo selection at the federal level, meaning PGD can be used to select for offspring of a particular gender or to rule out embryos that have an elevated risk of intellectual disability. (As Ball points out, it may be possible to adapt this testing to screen for embryos that are predicted to have exceptional cognitive ability.)

At the center of an adjacent debate are germline genome-editing technologies. As exemplified by the so-called “CRISPR-baby” controversy and expounded upon by Ball, access to, and affordability of, new biotechnologies may serve some segments of society while underserving others. Ball appeals to the democratic process to determine the balance between personal liberty and state-dictated equity, acknowledging that everyone has a stake in and therefore the right to be heard on this important issue.

Because of the immense power of emerging biotechnologies, those of us who are intimately involved with these advances must make a concerted effort to equip both policy-makers and the public with the knowledge and tools needed to navigate this evolving landscape. Ambitious and expansive, How to Grow a Human could be one piece of this effort—Ball’s look at the state of human-facing cutting-edge bioscience is a thought-provoking read.




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