What is astrobiology?

I suppose that “astrobiology” could be called one of those “ten dollar” words, but despite being a long word of six syllables and a dozen letters, it can be defined quite simply.

Astrobiology has been called, “The study of life in space” (Mix, Life in Space: Astrobiology for Everyone, 2009) and that, “Astrobiology… removes the distinction between life on our planet and life elsewhere.” (Plaxco and Gross, Astrobiology: A Brief Introduction, 2006). Taking these sententious formulations of astrobiology as the study of life in space, which removes the distinction between life on our planet and life elsewhere, together gives us a new perspective with which to view life on Earth (and beyond).

There are, of course, longer and more detailed definitions of astrobiology. There are two in particular that I have cited in previous posts:

“The study of the living universe. This field provides a scientific foundation for a multidisciplinary study of (1) the origin and distribution of life in the universe, (2) an understanding of the role of gravity in living systems, and (3) the study of the Earth’s atmospheres and ecosystems.”

from the NASA strategic plan of 1996, quoted in Steven J. Dick and James E. Strick, The Living Universe: NASA and the Development of Astrobiology, 2005


“Astrobiology is the study of the origin, evolution, distribution, and future of life in the universe. This multidisciplinary field encompasses the search for habitable environments in our Solar System and habitable planets outside our Solar System, the search for evidence of prebiotic chemistry and life on Mars and other bodies in our Solar System, laboratory and field research into the origins and early evolution of life on Earth, and studies of the potential for life to adapt to challenges on Earth and in space.”

from the NASA astrobiology website

I cited these two definitions of astrobiology from NASA in Eo-, Eso-, Exo-, Astro- and other posts in which I used parallel formulations to define astrocivilization.

Learning to take the astrobiological point of view

I‘ve posted a couple remarks about astrobiology on Twitter that I would like to repeat here to set the tone for what follows. More than two years ago I posted this on Twitter:

Astrobiology is island biogeography writ large.

This is one of the few “tweets” I’ve written that was “re-tweeted” multiple times (I’m not very popular on Twitter.) After I wrote this I began a more extensive blog post on this theme, but didn’t finish it; the topic rapidly became too large and started to look like a book rather than a post. Then last month I posted this on Twitter:

In the same way that Darwin provided a new perspective on life, astrobiology provides a novel perspective that allows us to see life anew.

Recently I’ve also been referring to astrobiology with increasing frequency in my blog posts, and I referenced astrobiology in my 2012 presentation at the 100YSS symposium in Houston and just last month in my presentation at the Icarus Interstellar Starship Congress in Dallas.

It will be apparent to the reader, then, then the idea of astrobiology has been slowly growing on me for the past few years, and the more I think about it, the more I come to realize the fundamentally new perspective that astrobiology offers on life and its evolution. Moreover, astrobiology also is suggestive for the future of life, and what we will discover about life the more we explore the cosmos.

Astrobiology: the Fourth Revolution in the Life Sciences

The more I think about astrobiology, the more I realize that, like earlier revolutions in the life sciences, the astrobiological point of view gives a novel perspective on familiar facts, and in so doing it potentially orients science in a new direction. For this reason I now see astrobiology as the fourth of four revolutions that instantiated the life sciences in their present form and continue to shape the way that we think about biology and the living world.

Here is my list of the four major revolutions in biological thought that have shaped the life sciences:

● Natural selection Independently discovered by Charles Darwin and Alfred Russel Wallace, natural selection gave sharpness of focus to many vague evolutionary ideas that were being circulated in the nineteenth century. With natural selection, biology had a theory by which to work, that could unify biological thought in a way that had not previously been possible. Of the Darwinian revolution Harald Brüssow wrote, “How can biologists cope conceptually and technically with this enormous species number? A deep sigh of relief came for biologists already in 1859 with the publication of Charles Darwin’s book ‘On the Origin of Species’. Suddenly, biologists had a unifying theory for their branch of science. One could even argue that the holy grail of a great unifying theory was achieved by Darwin and Wallace at a time when Maxwell was unifying physics, the older sister of biology, at the level of the electromagnetic field theory.” (“The not so universal tree of life or the place of viruses in the living world” Phil. Trans. R. Soc. B, 2009, 364, 2263–2274)

● Genetics After Darwin and Wallace came Gregor Mengel, who solved fundamental problems in the theory of inheritance and so greatly strengthened the Darwinian theory of descent with modification. As Darwin had provided the mechanism for the overall structure of life, Mendel provided the mechanism that made natural selection possible. Mendel’s work, contemporaneous with Darwin, was forgotten and not rediscovered until the early twentieth century. It was not until the middle of the twentieth century that Crick and Watson were able to delineate the structure of DNA, which made it possible to describe Mendelian genetics on a molecular level, thus making possible molecular biology.

● Evo-devo Evo-devo, which is a contraction of evolutionary developmental biology, once again went back to the roots of biology (as Darwin had done by formulating a fundamental theory, and as Mendel had done by his careful study of inheritance in pea plants), and returned the study of embryology to the center of attention of evolutionary biology. Studying the embryology of organisms with the tools of molecular biology gave (and continues to give) new insights into the fine structure of life’s evolution. Before evo-devo, few if any suspected that the homology that Darwin and others notes on a macro-biological scale (the structural similarity of the hand of a man, the wing of a bat, and the flipper of a dolphin) would be reducible to homology on a genetic level, but evo-devo has demonstrated this in remarkable ways, and in so doing has further underlined the unity of all terrestrial life.

● Astrobiology Astrobiology now lifts life out of its exclusively terrestrial context and studies life in its cosmological context. We have known for some time that climate is a major driver of evolution, and that climatology is in turn largely driven by the vicissitudes of the Earth as the Earth orbits the sun, exchanges material with other bodies in our solar system, and the solar system entire bobs up and down in the plane of the Milky Way galaxy. Of understanding of life gains immensely by being placed in the cosmological context, which forces us both to think big, in terms of the place of life in the universe, as well as to think small, in terms of the details of origins of life on Earth and its potential relation to life elsewhere in the universe.

This is obviously a list of revolutions in biological thought compiled by an outsider, i.e., by someone who is not a biologist. Others might well compile different lists. For example, I can easily imagine someone putting the Woesean revolution on a short list of revolutions in biological thought. Woese was largely responsible for replacing the tripartite division of animals, plants, and fungi with the tripartite division of the biological domains of Bacteria, Archaea and Eukarya. (There remains the question of where viruses fit in to this scheme, as discussed in the Brüssow paper cited above.)

tree-of-life 2

Since I have included molecular phylogeny among the developments of evo-devo (in the graphic at the bottom of this post), I have implicitly place Woese’s work within the evo-devo revolution, since it was the method of molecular phylogeny that made it possible to demonstrate that plants, animals and fungi are all closely related biologically, while the truly fundamental division in terrestrial life is between the eukarya (which includes plants, animals, and fungi, which are all multicellular organisms), bacteria, and archaea. If any biologists happen to read this, I hope you will be a bit indulgent toward my efforts, though I certainly encourage you to leave a comment if I have made any particularly egregious errors.

Toward a Radical Biology

Darwin mentioned the origins of life only briefly and in passing. There is the famous reference to, “some warm little pond with all sorts of ammonia and phosphoric salts, — light, heat, electricity &c. present” in his letter to Joseph Hooker, and there is the famous passage at the end of his Origin of Species which I discussed in Darwin’s Cosmology:

“Thus, from the war of nature, from famine and death, the most exalted object which we are capable of conceiving, namely, the production of the higher animals, directly follows. There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.”

Darwin, of course, had nothing to go on at this point. Trying to understand or explain the origins of life without molecular biology would be like trying to explain the nature of water without the atomic and molecular theory of matter: the conceptual infrastructure to circumscribe the most basic elements of life did not yet exist. (The example of trying to define water without the atomic theory of matter is employed by Robert M. Hazen in his lectures on the Origins of Life.)

Just as Darwin pressed biology beyond the collecting and comparison of beetles in the backyard, and opened up deep time to biology (and, vice versa, biology to deep time), so astrobiology presses forward with the project of evolutionary biology, pursuing the natural origins of life to its chemical antecedents. Astrobiology is a radical biology in the same way that Darwin was radical biology in his time: both go to the root to the matter to the extent possible given the theoretical, scientific, and technological parameters of thought. It is in the radical sense that astrobiology is integral with origins of life research; it is in this sense in which the two are one.

The humble origins of radical ideas

The radical biology of Darwin did not start out as such. In his early life, Darwin considered becoming a country parson, and when Darwin left on his voyage on the Beagle as Captain Fitzroy’s gentleman companion, he held mostly conventional views. It is easy to imagine an alternative history in which Darwin retained his conventional views, went on to become a country parson, and gave Sunday sermons that were mostly moral homilies punctuated by the occasional quote from scripture the illustrate the moral lesson with a story from the tradition he nominally represented. Such a Darwin from an alternative history would have continued to collect beetles during the week and would have maintained his interest in natural history.

Just as Darwin came out of the context of English natural history (which, before Darwin, gave us those classic works of teleology, Paley’s Natural Theology and Chambers’ Vestiges of the Natural History of Creation — a work that the young Darwin greatly admired), so too astrobiology comes out of the context of a later development of natural history — the scientific search for the origins of life and for extraterrestrial life. While the search for extraterrestrial life is “big science” of an order of magnitude only possible by an institution like NASA, in this respect it stands in the humble tradition of natural history, since we must send robots of Mars and the other planets until we can go there ourselves with a shovel and rock hammer. From such humble beginnings sometimes emerge radical consequences.

I think we are already beginning to see the potentially radical character of astrobiology, and that this development in biology promises a paradigm shift almost of the scope and magnitude of natural selection. Indeed, both natural selection and astrobiology can be understood as further (and radical) contextualizations of the theme of man’s place in nature. When Darwin wrote, he contextualized human history in the most comprehensive conception of nature then possible; today astrobiology must contextualize not only human history but also the totality of life on Earth in a much more comprehensive cosmological context.

As our knowledge of the world (which was once very small, and very parochial) steadily expands, we are eventually forced to extend and refine our concepts in order to adequately account for the world that we now know. Natural selection and astrobiology are steps in the extension and refinement of our conception of life, and of the place of life in the world. Life simpliciter is, after all, a “folk” concept. Indeed, “life” is folk biology and “world” is folk cosmology. Astrobiology brings together these folk concepts and attempts to bring scientific rigor to them.

The biology of the future

Astrobiology is laying the foundations for the biology of the future. Here and now on earth, without having surveyed life on other worlds, astrobiologists are attempting for formulate concepts adequate to understanding life at the largest and the smallest scales. Once we take these conceptions along with us when we eventually explore alien worlds — including alien worlds close to home, such as Mars and the ocean beneath the ice of Europa — it is to be expected that further revolutions in the life sciences will come about as a result of attempting to understand what we eventually find in the light of the concepts we have preemptively developed in order to understand biology beyond the surface of the Earth.

Future revolutions in biology will likely have the same radical character as natural selection, genetics, evo-devo, and astrobiology. Future naturalists will do what naturalists do best: they will spend their time in the field finding new specimens and describing them for science, and in the process of the slow and incremental accumulation of scientific knowledge new ideas will suggest themselves. Perhaps someone laid low by some alien fever, like Wallace tossing and turning as he suffered from a fever in the Indonesian archipelago, will, in a moment of insight, rise from their sick bed long enough to dash off a revolutionary paper, sending it off to another naturalist, now settled and meditating over his own experiences of new and unfamiliar forms of life.

The naturalists of alien forms of life will not necessarily have the same point of view as that of astrobiologists — and that is all to the good. Science thrives when it is enriched by new perspectives. At present, the revolutionary new perspective is astrobiology, but that will not likely remain true indefinitely.

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four revolutions

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Grand Strategy Annex

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