Evolutionary Anthropology 13:5–10 (2004) CROTCHETS & QUIDDITIES The Frog in Taffeta Pants KENNETH WEISS What is the magic that makes dead flesh fly? himself gave up on the preformation view). These various intuitions arise natu- Where does a new life come from? manded explanation. There was no rally, if sometimes fancifully. The nat- Before there were microscopes, and compelling reason to think that what uralist Henry Bates observed that the before the cell theory, this was not a one needed to find was too small to natives in the village of Aveyros, up trivial question. Centuries of answers see. Aristotle hypothesized epigenesis, the Tapajos tributary to the Amazon, were pure guesswork by today’s stan- a kind of spontaneous generation of believed the fire ants, that plagued dards, but they had deep implications life from the required materials (pro- them horribly, sprang up from the for the understanding of life. The vided in the egg), that systematic ob- blood of slaughtered victims of the re- 5 phrase spontaneous generation has servation suggested coalesced into a bellion of 1835–1836 in Brazil. In gone out of our vocabulary except as chick. Such notions persisted for cen- fact, Greek mythology is full of beings an historical relic, reflecting a total turies into what we will see was the spontaneously arising—snakes from success of two centuries of biological critical 17th century, when the follow- Medusa’s blood, Aphrodite from sea- research.1 The realization that a new ing alchemist’s recipe was offered for foam, and others. Even when the organism is always generated from the production of mice:3,4 mix sweaty truth is known, we can be similarly one or more cells shed by parents ex- underwear and wheat husks; store in impressed with the phenomena of plained how something could arise open-mouthed jar for 21 days; the generation. John Muir observed, “The where nothing could be seen. sweat will penetrate the wheat, chang- bluebottle is abundant in these Yo- However, if this solved one question ing it into mice. semite woods, ever ready with his about the origin of organisms, it left a There was an equally persistent al- marvelous store of eggs to make all 6 related problem that is still with us, ternative view. In 50 BC, Lucretius (de dead flesh fly.” that of explaining autonomous gener- Rerum Natura) wrote that “The first ation—development—which has be- bodies of each thing must be inside TWO CENTURIES AT THE HEART come a core question in modern biol- the seed; because of this all things can ogy and genetics, and is relevant to the not arise from anything. For each par- OF BIOLOGY physical and behavioral traits that are ticular seed has, in itself, hidden in- The scientific assault on the ques- at the heart of anthropology. Where side its own distinctive powers.” It tion began in earnest in the 17th cen- do they come from each generation? seemed reasonable to assume conti- tury,2,7 but took two centuries to com- nuity in nature, so that what we see plete. The most famous example of OMNE VIVUM EX VIVO? reflects what happens before we can spontaneous generation was the ap- see it, making it logical to infer that pearance of maggots in dead meat. In The ancients knew about parents either the sperm or egg contained a 1668 Francesco Redi (Figure 2) per- producing offspring of their own kind, future organism in miniature, an is- formed a classic study8 that some con- but also that there isn’t a chicken in- sue long and hotly debated between sider to have been the first controlled side an egg when it is freshly laid.1,2 It the “ovist” and “spermist” schools of experiments in the history of science. was not just a lack of microscopes that thought. The imagery of preformation He put dead flesh in an open dish, in made this latter fact one that de- has been made famous by countless which maggots soon appeared as ex- reprinting of Nicolaas Hartsoeker’s pected. I never realized until I re- 1694 AD drawing (Figure 1). An impli- peated the experiment for this column cation was that an organism’s gonads (Figure 3) that if you were not aware Ken Weiss is a biological anthropologist, contain, in ever more miniaturized of the tiny fly eggs, the maggots make at Penn State University. E-mail: kmw4@ and nested form, the preformed em- psu.edu their appearance, dramatically, bur- bryos of all its potential future descen- rowing out from the inside, the whole dants. Biblical scholars related this to piece of flesh subsequently throbbing © 2004 Wiley-Liss, Inc. a preordained course of human be- like a heart before being transformed DOI 10.1002/evan.30001 Published online in Wiley InterScience ings from Adam to Armageddon almost entirely into maggot. No won- (www.interscience.wiley.com). (though after later work, Hartsoeker der the explanation that had been 6 Weiss CROTCHETS & QUIDDITIES swarming around the gauze and lay- count their persistence in centuries,”4 ing eggs on it that quickly hatched as but that did not make them right. A maggots. Dead flesh does not fly of its fighter like Huxley, he was determined own accord. to prove the errors of rivals like the This was not entirely the end of a famous Comte de Buffon and his own story whose importance even to late peer Felix Pouchet, who advocated 19th century science was reflected in molecular vitalistic versions of epi- the famous 1870 Presidential address genesis. In experiments beginning in by Thomas Huxley (Figure 4) to the Darwin’s year, 1859, that essentially British Association for the Advance- refined Redi’s logic, Pasteur placed ment of Science.9 If Redi had shown fresh, boiled broth in a flask con- that complex animals like insects did structed with an S-shaped neck that not arise spontaneously, this did not kept microorganisms from settling account for the appearance of tiny from the air onto the broth, and no “animalcules” when substances like fermentation occurred. With this beef broth, infusions of grain or hay, proof that microbes, too, arise only grapes, and many other things de- from parents of like type, Pasteur pro- cayed or fermented. These had been vided another instance of what Hux- observed since the early days of mi- ley called “the great tragedy of Sci- croscopy. Could this simple form of ence—the slaying of a beautiful life arise spontaneously? Attempts to hypothesis by an ugly fact.” Not even repeat Redi’s experiments in regard to tiny microbes arise by themselves. the origin of this primitive life-form I’m omitting many details of a long were notoriously inconsistent, ex- history,1,2,7 but Pasteur and Huxley plaining why the issue could remain were both clear about the importance for so long a central question in biol- of a proper understanding of micro- ogy. The problem (we now know) was bial generation. That had enormous the incomplete elimination of boiling- implications for agricultural pest con- resistant spores, cells too small to fil- trol and manufacturing (e.g., wine, ter by the means that were tried, and baking, beer, silk), and for public the ubiquity of microbial life in the air health. Huxley raised the additional around us. and unanswered question of xenogen- The fermentation question was fi- esis, the appearance of animal tumors nally put to rest by the vigorous ener- and plant galls: what form of new life Figure 1. Homunculus (Hartsoeker, 1694, Es- gies of another of the century’s great were these, that sprung up within an say de Dioptrique). science entrepreneurs, Louis Pasteur organism? (Figure 5), in promoting his microbial If even complex organisms come given! But if Redi covered an identical view of the world. In an 1864 address from other life, what is the contribu- container with fine gauze, no maggots to the Sorbonne Scientific Soire´e he tion of male and female and why are appeared. Instead, he observed flies noted that “the most striking errors both needed? Was the fly contained in Figure 2. Pioneers (A) Francesco Redi. (B) Title page (5th ed., 1688). (C) Lazzaro Spallanzani. Portrait sources: Spallanzani www. chemheritage.org/EducationalServices/pharm/antibiot/activity/spapas.htm Redi: www.francescoredi.it/ CROTCHETS & QUIDDITIES The Frog in Taffeta Pants 7 Figure 3. Redi redux triptych (2003 AD). (A) Fly desirous. (B) Fly eggs after 24 hours (arrows show a few). (C) Riddled with maggots and pulsating after 48 more hours (arrows show a few). the egg, or sperm? We think of ovists tity needing only chemical stimula- teins and other compounds; 3) ligand- versus spermists as quaint naivety, tion by the seminal fluid.1,7 Actually, receptor binding involved in the but when microscopists demonstrated in the end Spallanzani concluded that receipt of extracellular signals that parthenogenesis in aphids, it seemed something in the thicker fraction of change gene expression within cells; an important issue. To address it, Laz- semen was responsible, because he 4) protein-DNA binding that allows zaro Spallanzani (Figure 2) per- could not accept that it was its wriggly transcription factor proteins to ex- formed a series of clever experiments contaminants. press or repress specific genes based in the 1760s. Semen was known from on regulatory sequences in DNA lo- microscopy to contain wormified be- THE MODERN VIEW: cated near the genes;13 and 5) the ings in a thicker component, and a AUTONOMOUS GENERATION sensing of extra-cellular conditions thinner liquid. Spallanzani dressed (such as pH or salt concentrations) to male frogs in tight-fitting taffeta pants Hartsoeker’s homunculus and frogs which cells can actively adjust (e.g., and let them “seek the female with wearing taffeta condoms draw smiles, ion channels, neurotransmission).