Relics, replicas and commemorationsSoraya de Chadarevian
Department of History and Philosophy of Science, University of Cambridge, Free School Lane, Cambridge, CB2 3RH, UK
Several replicas of Watson and Cricks demonstrationmodel of DNA built at the Cavendish Laboratory inCambridge in 1953 exist, but where is the original?Once the object of intense discussion but soon super-seded by more refined models built at Kings CollegeLondon, it slowly fell to pieces and was eventually dis-assembled. Twenty years after it was first constructed,some of its pieces resurfaced at Bristol. By that time,the value attached to the original incarnation of thedouble helix had changed substantially, and the ScienceMuseum in London commissioned a replica of themodel, with some of the original parts built into it. Themodel was hailed as the nearest there is to the original.It has since served as prototype for further replicas.Meanwhile the spidery model of DNA has become theultimate icon of 20th-century life sciences, and morepieces supposedly belonging to the original continueto appear at auction.
In 1971, Arthur Arnone, one of many young Americanresearchers spending a three-year postdoctoral stint at the
world-famous Medical Research Council (MRC) Laboratoryof Molecular Biology (LMB) in Cambridge, detected a fewmetal plates among other jigs on a dusty bench in themodel-building room . Arnone picked up what herecognized as an adenine base, one of the four basespresent in nucleic acids. In that moment, Francis Crickwalked by the door. Cheerfully he confirmed that hethought it was one of the bases he and James Watson hadused to build their DNA model in 1953, almost 20 yearsearlier when the laboratory was still housed in thephysics department. Arnone got him to sign the basewith an ink marker. When Watson visited thelaboratory a year later, he managed to make him addhis signature on the back.
Arnone has remained the fond custodian of the originalbase for over 30 years. Once a year, when he gave hislectures on DNA structure at the University of Iowa, hewould bring the base along for the students to see, but nottouch. Invariably he earned their spontaneous applause.He has now returned the base to the Cambridge laboratoryfor the 50th anniversary of the double helix (Fig. 1).
Fig. 1. Base plate (with central hole) collected by Arthur Arnone in Cambridge in 1971 and signed by Francis Crick and (on the other side) by James Watson. The function of
the red color mark is unknown. The plate is currently on display in the exhibition Representations of the Double Helix at the Whipple Museum of the History of Science in
Cambridge. Photograph by Leslie McKeany. Courtesy of the Medical Research Council Laboratory of Molecular Biology, Cambridge.
Corresponding author: Soraya de Chadarevian (firstname.lastname@example.org).
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If, in this anniversary year, we want to pay a visit to thecelebrated structure, a good bet is the Science Museum inLondon, which boasts not one, but two DNA models withmetal plates and spidery backbone that are, on first sight,almost indistinguishable from each other. Yet anothermodel has recently been built in the workshop of the LMBin Cambridge for display in the Whipple Museum of theHistory of Science. However, Watson and Cricks originalmodel no longer exists, and Arnones base plate is only oneof a confusing number of such plates held in private handor by museums.
Despite the importance attributed to the model in theaccounts of Watson and Cricks discovery of the DNAdouble helix, little is known about its actual fate. This is allthe more surprising given the value attached to physicalartefacts of the event. Tracing the busy career of Watsonand Cricks model provides unique insights into themaking of a 20th-century icon.
A model six-feet tallWhat then happened to the model Watson and Crick builtin 1953? First, we need to clarify which model we speak of.Model building was Watson and Cricks main approach intheir attempt to interpret available data, much of itproduced by Rosalind Franklin and her research studentRaymond Gosling at Kings College London, and thus todeduce the three-dimensional structure of DNA. Caltechscientist Linus Paulings success in determining thestructure of the polypeptide chain in proteins throughmodel building had convinced the two researchers of thepower of the method. Watson and Crick built many modelsthat were quickly dismantled because the suggestedstructures did not lead to any satisfactory solution. Fortheir various attempts they used the brass skeletal modelbuilding parts that were in the Cambridge laboratory forprotein modeling. Whilst playing with cardboard models ofthe bases, drawn according to Jerry Donohues suggestionof the prevalent forms in which the bases occurred in thecell, Watson fell upon the mechanism of base pairing theactual novel feature of their structure. The schematic 2D(rather than 3D) representation of the bases certainlyfacilitated Watsons work, just as the paper model of thepolypeptide chain had helped Pauling, although this is apoint often lost in anecdotal details. Watson had orderedmetal cut-outs of the bases from the Cavendish workshop. These took several days to produce. Getting impatient,he and Crick started building models with the usualskeletal building parts for the backbone and just aconstraint for the bases, at this point confidently placedat the inside of the two helical chains. Probably severalsuch models were built, although no photographic or otherrecord of these working structures survives . Thismeans that the model we know from the famous picture,taken in May 1953 by Cambridge freelance photographerAntony Barrington Brown, was not Watson and Cricksactual working model but a later model, built fordemonstration . Indeed, when a photograph of themodel first appeared in print in Watsons best-selling TheDouble Helix, the caption read: the original demonstrationmodel of the double helix  (Fig. 2).
This photograph, probably taken at a Cavendish open
day in July 1953, and Barrington Browns photograph originally taken to accompany a report on Watson andCricks discovery in Time magazine (but not published atthe time) are, to my knowledge, the only extant picturesof the model. None of them appeared in the scientificpublications on the structure. Rather, Watson and Cricksfirst publication in Nature, drafted before the demon-stration model was completed, included only a diagram-matic sketch of the structure, drawn by Cricks wife Odile,whilst a later paper giving a fuller description of thestructure featured photographs of a rough scale modelbuilt in the Cavendish workshop for use in the lectureroom . Nevertheless, the two casual photographsplayed a pivotal role in the subsequent history of themodel.
There was no press conference following Watson andCricks conclusion of their work on the structure. This wasnot part of British academic culture at the time . Inaddition, the proposed structure was not more than ahypothetical model and still awaited to be tested againstmore accurate experimental data. The six-feet tall modelstanding in Watson and Cricks office in the Cavendishnonetheless served to convince fellow scientists andimpress foundation officers. Visitors came to see themodel in the flesh.
Fig. 2. The original demonstration model of the double helix (probably July
1953). Photographer unknown. Courtesy of the James D. Watson Collection, Cold
Spring Harbor Laboratory Archives.
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Yet the fragile construction was not built to last. In oneof Barrington Browns discarded photographs, we seeCrick repairing the structure when it was not more than afew weeks old. Soon, it also emerged that the structure wasnot correct in all detail. Pauling for one showed that thetwo bases guanine and cytosine were held together bythree rather than by two hydrogen bridges as had beensuggested by Watson and Crick. The bases were alsomoved too far from the central axis of the structure. Moreprecise measurements of various parameters soon led tothe construction of more accurate models at Kings CollegeLondon . Watson and Cricks model neverthelesssurvived in the Cavendish until the early 1960s, whenthe group moved to the newly built LMB on the outskirts ofCambridge. In the autumn of 1962, the same year as themove, Watson and Crick, together with Maurice Wilkins,were awarded the Nobel Prize for their work on thestructure of DNA.
In the new laboratory, the model found a place in thecommunal model room, but soon became neglected. Moreand more pieces broke away. Nobody seemed to bothermuch. Eventually, the dilapidated model was dismantledand as was usual practice, its parts were mixed up withother modeling material to be used for new model buildingprojects.
From Bristol to LondonArnone may well have been the first to turn a remnantfrom Watson and Cricks model into a relic, a historicalitem worth collecting. The autographed piece also servedas a memento or souvenir of his time at the prestigiousLMB, where he crossed paths with Crick, Watson andothers who had become leading figures in the field.
Nonetheless, Arnone was lucky to come across someforgotten plates in a dusty corner of the model room.Shortly before he came to the laboratory, several metalplates had been packed up apparently inadvertently so with other model-building material for protein crystal-lographer Herman Watson when he moved fromCambridge to take up a position in Bristol. It wascustomary for scientists to take their model materialwith them when moving. Packing was done by techniciansin the laboratory. As