Live Long and Evolve: What Star Trek Can Teach Us about Evolution, Genetics, and Life on Other Worlds

ISBN-13: 9780691203935

Media Type: Paperback

Publisher: Princeton University Press

Publication Date: 02-25-2020

Pages: 208

Product Dimensions: 4.90(w) x 7.90(h) x 0.50(d)

Mohamed A. F. Noor, besides being a Trekkie, is a professor in the Biology Department and the Dean of Natural Sciences at Duke University

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CHAPTER 1

"TO SEEK OUT NEW LIFE ..."

The opening sequences of both TOS and TNG mention that their mission is "to seek out new life." While many viewers think of this mission in the context of other humanoid life forms depicted in the series, such as the Vulcans or Klingons or Andorians, fewer think of it in the context of entirely unfamiliar forms. Is such unfamiliar life likely, and what might a "new life form" look like? The first section of this chapter examines briefly the question of what "life" actually means and begins to examine its probability of occurrence. Many biology textbooks provide lists of characteristics of living organisms, but exceptions to some items in these lists abound even on our own planet. Might we expect similar forms to have arisen elsewhere in the universe? Furthermore, these lists are artificial in the sense that they were made based on observations of known organisms on Earth rather than derived from fundamental principles of biology and chemistry. Much of life is, for example, water and carbon based, but are these properties general to life or idiosyncratic to the observed single set of related life forms on Earth? The second section of the chapter goes into several properties associated with life on Earth, and considers what alternatives may be possible.

TNG, Season 6, Episode 9, "Quality of Life"

Lieutenant Commander Data is an android but has been considered throughout the series to be alive and self-aware. In this episode, he begins to question whether other machines he encountered are alive. He goes to the ship's chief medical officer, Beverly Crusher, and asks what the definition of life is. She answers that "the broadest scientific definition might be that life is what enables plants and animals to consume food, derive energy from it, grow, adapt themselves to their surroundings, and reproduce." Data is dissatisfied with this answer, noting fire "consumes fuel to produce energy, it grows, it creates offspring." He then elaborates on an exception in the other direction, noting about himself that he does not grow or reproduce yet is considered alive. He further raises the question of whether something specific transpired to endow him with life between when he was merely component parts and when he became alive.

DEFINING LIFE

Much science-fiction writing and film (Star Trek or otherwise) considers the possibility of life on other worlds. We all ponder how likely extraterrestrial life is to arise and what form such life might take. To answer these questions, we need some idea of how to define life so that we may determine its likelihood and recognize it when we come upon it. To define life, we humans naturally first consider forms of life with which we are most familiar: life on Earth. We know that animals, plants, and fungi are alive. We are similarly convinced that various microscopic forms including bacteria, amoebae, and the parasite that causes giardia are alive. What attributes do these forms share? The textbook list of traits associated with life is similar to the ones that Doctor Crusher laid out in TNG "Quality of Life" above: acquiring or producing energy, some level of internal organization, maintenance of a constant internal environment, growth, reproduction, response to stimuli, and ability to adapt over generations. Physicist Erwin Schrödinger highlighted in 1944 that living matter evades the decay to equilibrium. Nonliving matter (whether never alive or now dead) tends to move to equilibrium with its environment: reaching a similar temperature, not growing or moving unless impacted by outside forces, etc. Life forms expend energy to remain distinct and out of equilibrium relative to their environment.

Let me use a bacterium that causes pneumonia, Streptococcus pneumoniae, as an illustrative example. It appears in the form of individual cells as units of life. Each cell takes up simple carbohydrates from its environment to use for energy; each has a defined structure with a wall and several specific surface proteins to maintain the internal environment; each has internal structures including a chromosome containing instructions for maintenance and reproduction; each grows and reproduces; each produces specific proteins in response to antibiotics; and several cell lineages have evolved over time, in some cases, unfortunately for us, to become resistant to commonly used antibiotics. Unambiguously, Streptococcus pneumoniae cells are alive.

While seemingly simple in some cases, defining life becomes a challenge when there is a mismatch between the list of characteristics and our instincts on whether something is alive. As Data noted, fire converts matter in its surroundings to energy and grows. A small spark from a fire can allow a separate fire to emerge, analogous to reproduction. Nonetheless, no biologist argues that fire is alive. Our homes have internal organization and a constant internal environment in some respects, but we do not perceive them to be alive. On the other side, many organisms we presume to be alive — in addition to the android Data — are also unable to reproduce, such as the mule (the sterile hybrid offspring of a horse and donkey: see chapter 5). Besides reproduction, other attributes associated with life are not "essential" for life: we would not declare an individual "nonliving" solely because it failed to grow or if it reproduced as completely identical clones so that there was no potential to adapt over time.

There are also gray areas. Are viruses alive? Viruses require nonvirus host cells for reproduction, so they cannot reproduce independently. They do not generate or store energy but instead rely on host cells for energy for all functions. Some scientists have argued that these properties make them too dependent on other life forms to be considered alive. However, many living organisms are dependent on other individuals or species for their lives or reproduction. Medical professionals often talk about "killing viruses," which implies that they are alive. Recent work shows individual viruses even exhibit a form of chemical communication that affects the behavior of other viruses. Overall, biologists are split on the question of whether viruses are alive or merely natural replicators that capitalize on and influence other living organisms. Viruses are not the only gray area. Transposable elements (DNA sequences that insert themselves into genomes and then make copies of themselves) and prions (misfolded proteins that change other proteins near them to their misfolded state) also self-replicate in a sense, but they are considered to be further from "living" than viruses. As these examples illustrate, there is no simple solution to defining life. In essence, "life" is an imprecise term used to define having many of a suite of particular traits, but with no specific number or absolute requirements of which traits from the suite must be included.

Despite this uncertainty, some very reputable biologists, including Nobel laureates, have argued that defining life precisely is not necessary for us to study the likelihood of life to arise or its possible origins. We still know many important components, and those can be researched individually or in groups. Life as we know it arguably has a chemical basis; venturing outside that constraint generally falls into the realms of philosophy and religion. With that in mind, some scientists have suggested that life can be described as a sustained chemical system that undergoes self-reproduction with the potential for some change over time (i.e., evolution).

GENERATING NEW LIFE

If the simplest form of new life is a sustained chemical system like that described above, such life has already been constructed in the laboratory using building blocks from existing life: specifically synthesized fragments of the nucleic acid RNA (also discussed in chapter 3). The first life on Earth may well have used RNA for heredity, since, unlike DNA or proteins, RNA has the ability to both transmit hereditary information and carry out some vital functions of the cell. Indeed, RNA is involved in the transmission of genetic information in some present-day viruses, such as HIV. Self-replicating combinations of RNA "instructions" have been assembled in the laboratory that, in the presence of the appropriate raw materials, make more copies of themselves without any added directions or machinery (e.g., enzymes). More recent studies have given these RNAs the ability to produce other types of functional molecules. Hence, some of the most plausible models for early life on Earth include an RNA-based phase, making this particular example especially interesting for understanding the history of life on our own planet. Still, self-replication of genetic material alone does not make a "cell" as we know it today — metabolic processes must also occur, and the cell-replication machinery must remain physically distinct from its immediate surroundings. On the latter point, recent progress has been made in describing how membranes also may have evolved, to keep cells distinct.

Would the raw materials for life have been available on early prelife Earth, though? A famous experiment, published in 1953 by Stanley Miller, showed that amino acids, the building blocks of proteins, can form naturally without preexisting life in the presence of hydrogen, ammonia, methane, and water, when exposed to sparks (analogous to lightning). While we do not know with certainty the exact chemicals or their concentrations on Earth before life formed, these compounds are widespread in the universe, and related results were found in later studies using different chemicals (e.g., hydrogen sulfide) or different conditions. Additionally, numerical models suggest that long RNA molecules, potentially able to initiate primitive life, could have formed more than four billion years ago on Earth in the conditions present at the time. Altogether, the potential seems high for having the known raw materials for Earthlike life arise spontaneously in the universe.

Much of the text above focuses on the question of how life on Earth might have arisen — understanding a specific instance. If one is considering life on other worlds, we must focus on the more general question: how might life arise? While the studies described above provide elegant proof of principle of the origin of basic life components from nonlife on an early Earth, they may not reflect the potential for life on other worlds accurately.

As such, a few scientists have taken an even more basic physical view in exploring the potential for the conditions associated with life to arise. Earth is an "open system," in that not only do interactions happen between organisms and resources on the planet, but also energy is continually being provided to the planet via radiation from the sun. Many systems tend to spread energy out over time (increasing entropy, as per the second law of thermodynamics), but open systems can divide energy unequally since they are influenced by and can influence their surroundings. Under such conditions, and if surrounded by a liquid or gas (e.g., our planet's oceans or atmosphere), theory suggests that matter may often gradually restructure itself so as to dissipate greater amounts of heat energy. Some physical scientists have argued that self-replication (reproduction) may achieve this outcome, since replication dissipates energy in an irreversible manner (i.e., one organism is more likely to replicate into two than two organisms are to fuse into one). General thermodynamic definitions of evolution predate this particular model, and certainly the applicability of this argument to the origin of life in particular is tenuous. However, the argument described above adds new dimensions, suggesting why processes associated with life may be somewhat likely to arise from basic principles of physics.

Taking all of the above together, "life" on other worlds may be simple and reasonably probable to exist but could arguably be chemical processes quite unlike the humanoid aliens observed in much of Star Trek or other science fiction. Such forms may be extremely difficult to notice, even from very close, and simple "scans" from space, such as those conducted in Star Trek, may easily miss them. Instead, Star Trek devotes much attention to the "sentience" of life across the series: the crews often struggle to determine whether organisms that they encounter are self-aware. Undoubtedly, self-awareness would indicate that an entity is alive, but the vast majority of organisms we know or predict would not have this characteristic.

NEW LIFE IN STAR TREK

As in the example at the start of this section, Star Trek does consider the potential for life among constructed forms, in which the life-related processes may be electrical rather than chemical and some exceptions to the "characteristics of life" may apply. Two examples used in the series regularly are the TNG android character Data and the VOY holographic doctor. Both characters are essentially animated computer programs, yet both have most or all of the characteristics of life and are even self-aware. In fact, both reproduced in some sense: in TNG "The Offspring," Data built a child (Lal) using neural transfers from himself, while in VOY "Real Life," the holographic doctor created a holographic wife and children. Are these truly "offspring"? Counselor Troi emphasized to Captain Picard, "Why should biology rather than technology determine whether it is a child? Data has created an offspring. A new life out of his own being." Can a "manufactured" form be considered alive? Multiple religions suggest that existing species (including humans) were designed by a living creator, and no one argues that such a premise would mean the products are "not living." Hence, constructed forms can be considered alive in principle, and we may be close to producing human-made forms that can be considered alive. One might wonder if perhaps the first new life we encounter may be a form that either we made ourselves or that others manufactured and sent out into the cosmos.

Nonetheless, when biologists discuss the origin of life, they typically consider life arising from raw materials of nonlife, and not initiated or produced by extant living forms. In that regard, while androids or computer programs may fit the definition of life, they did not arise from nonlife. I suggest a separation of "origin of life from nonlife" and "origin of new life from existing, albeit different, life." Although many Star Trek episodes are devoted to the latter, fewer focus on the former. One passing reference was made in the DS9 episode "Playing God" to potential new life evidenced by "nonrandom thermodynamics," akin to the basic physical view discussed above. However, few (if any) other references exist across the series.

HOW MUCH SHOULD LIFE ON EARTH RESEMBLE EXTRATERRESTRIAL LIFE?

Life forms on Earth are made from carbon-containing compounds and use water for their biochemical reactions. Many Earth life forms thrive at temperatures between 5°C and 40°C and release energy from respired oxygen. Should we expect extraterrestrial life to share such characteristics? The problem with extrapolation is that all of life on Earth is related in a strict sense: we share a common ancestor with every life form known on this planet (a topic discussed at greater length in chapter 2). Hence, while we know many life forms on Earth are water and carbon based, all of those forms are nonindependent, creating a problem for predicting what we may see elsewhere. This problem is analogous to predicting the characteristics of a "sport" having only known soccer and some sports derived from it (e.g., American football). Knowing these sports, one might then predict "sports" to involve teams, scores, and putting an object into a goal defended by an opponent. While these attributes apply for some sports, like basketball or hockey, how well would such predictions apply to fencing or surfing? What about karate or boxing? Many sports have some means of scoring (albeit measured in very different ways) but do not involve putting objects into defended goals.

Through the next sections, we will consider a few specific characteristics of life on Earth, variations thereof observed on Earth, and, when possible, arguments for whether they may be typical or exceptional on other worlds. We will also look at whether and how variations were explored in the Star Trek series. In principle, one should predict that life forms on other worlds and in Star Trek should be more diverse than life on Earth if they do not share evolutionary ancestors with each other and with Earth's life forms (but see chapter 2) — analogous to how unrelated people often exhibit greater variation in features than do genetically related people within a single family. Some of this predicted greater diversity is indeed reflected in the series.

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Excerpted from "Live Long and Evolve"
by .
Copyright © 2018 Mohamed A. F. Noor.
Excerpted by permission of PRINCETON UNIVERSITY PRESS.
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Table of Contents

Preface, vii,
Acknowledgments, xi,
Abbreviations for Star Trek Series, xiii,
Chapter 1. "To Seek Out New Life ...", 1,
Chapter 2. Charting the Relationships of Species, 30,
Chapter 3. DNA: Evolution's Captain, 56,
Chapter 4. Change over Time: Drivers of Evolution, 81,
Chapter 5. Sex, Reproduction, and the Making of New Species, 106,
Chapter 6. Science versus Science Fiction, 132,
Appendix: Mining Gems and Coal, 143,
Notes, 157,
Suggested Associated Scientific Reading, 177,
Star Trek Episode Index, 181,
Subject Index, 185,