Biological issues in Jurassic Park
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Jurassic Park, a book by Michael Crichton, with a film version directed by Steven Spielberg, revolves around the resurrection of dinosaurs via genetic engineering. Scientists and enthusiasts have brought up a number of issues with their facts and feasibility.
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[edit] Dinosaurs
[edit] Velociraptor
The raptors in the novel, following through to the film raptors, were larger than the species going by the name because during the writing of the novel, a previously discovered dinosaur named Deinonychus (closely related to Velociraptor, but larger) was rechristened as a Velociraptor species by some scientists, notably Gregory S. Paul. Crichton wrote his novel based on the idea of a human sized raptor, but after the publication --when the movie was already in production--the idea of Deinonychus being a Velociraptor species was dropped.
During the movie's production, the effects supervisors acknowledged that the Velociraptors featured in the movie were sized identically to the larger Deinonychus. However, during the filming paleontologists came across a larger dromaeosaurid species named Utahraptor and the larger raptors remained, even though Utahraptor was substantially larger (21 feet long) than the movie's raptors. It should be noted, also, that at the start of the film a Velociraptor skeleton is uncovered in Montana - no examples of the dinosaur have yet been uncovered in the USA (although both Deinonychus and Utahraptor are American dinosaurs). The fossil skeleton is similarly inaccurately large.
The intelligence of the Velociraptors in the films is considered somewhat unlikely by scientists, given the relative size of their brains and comparisons with contemporary animals.
It is highly likely that Velociraptor had feathers. Both the film and novel dinosaurs have scales, rather than feathers; however, both were created before the discovery of feathered dinosaurs closely related to Velociraptor (e.g. Microraptor). In Jurassic Park III the raptor was remodelled and small feathers on the male's heads were included in reference to this, while still looking similar to the original design.
[edit] Procompsognathus
The Procompsognathus in the novel secrete a venom described as similar to that of a cobra, although more primitive. Such an ability is purely speculative; there is no evidence to support it and scientists consider it unlikely. This ability to incapacitate their prey is absent in the films, where they are dropped in favour of Compsognathus.
[edit] Dilophosaurus
The Dilophosaurus in the movie is smaller than their 6 m (20ft) real-life counterparts, and has a totally speculative frill like the Australian frill-necked lizard. The frill/venom is purely Crichton's creative license. When first discovered, paleontologists found small holes in a dilophosaurus jaw, which were thought to be the remnants of venom glands.
[edit] Brachiosaurus
The Brachiosaurus in the movie was shown to be chewing its food, like a cow. In reality, it couldn't, as its teeth were specialized in stripping leaf matter from the branches, to then be swallowed whole. In the stomach, there were "gastroliths", rocks swallowed to grind up the plant matter to enable the animal to digest the plants. In addition, it is seen to raise up on its hind legs - as its forelimbs were longer and heavier, this seems very unlikely, as the animal could potentially have injured itself. Furthermore, it is seen chewing eucalyptus leaves, which are extremely potent. So far, it is believed only koalas have developed an immunity to the tree's vegetation.
[edit] Tyrannosaurus
The movie's theory is that the Tyrannosaurus rex would be unable to "see" someone if they were to remain still, though some argue that it would still be able to smell them (it was raining in the film, so the tyrannosaur's sense of smell would have been somewhat hindered). The book was ambiguous on the subject, though it hints that this is more the result of having the tyrannosaur's DNA blended with that of frogs. The movie's Tyrannosaurus also features anatomical differences to its real-life counterpart - namely it has a shorter, more box-shaped head and weaker, more spindly forelimbs (the real life T. rex having short, but massively muscled 'arms'). In addition, it is depicted as being able to keep pace with a jeep travelling at considerable speed (in the region of 40mph or more); scientific studies have shown that in reality, such a speed would have been impossible. Indeed, animators at Industrial Light and Magic were forced to use optical illusions in order to make the Tyrannosaurus appear to convincingly run at that speed[citation needed]; when animated accurately, it was said that the T. rex's legs flailed absurdly.
[edit] Pteranodon
The depiction in Jurassic Park III featured many inaccuracies, including toothed jaws, exaggerated strength and, presumably, aggression. Pteranodon is thought to have eaten fish, and was incapable of grasping with its feet.
[edit] Other issues
During a scene in the movie where traitorous park programmer Dennis Nedry steals the dinosaur DNA, some of the tubes on which the dinosaurs' names are printed have them spelled incorrectly, including Tyrannosaurus and Stegosaurus, as Tyranosaurus and Stegasaurus, respectively. The scene also shows Nedry opening up a liquid nitrogen-filled cryonic container and handling the supercooled tubes without thermal gloves. Doing this can be quite painful and causes severe frostbite, but nonetheless can be done for very brief periods, as shown.
The antennae of the fossil mosquito trapped in amber at the beginning of the film are fuzzy. This indicates that the insect is male, but only the females are bloodsuckers.
[edit] Biotechnological background
The dinosaur DNA is extracted from fossilized mosquitos, and this small amount is then amplified by polymerase chain reaction (PCR). This has been done before, for example with a Cretaceous weevil in Cano et al. (1993) (no dinosaur DNA was found).
There are some problems with this approach:
- Foremost, the DNA featured in the movie is shown coming from a Dominican amber mine, although it is never said to be the sole source. Dominican amber is approximately 30 million years old. Dinosaurs died out 65 million years ago.
- None of the dinosaurs featured in the movie are known to have existed in the Dominican Republic 65 million years ago.
- The mosquito had to have had just one species of dinosaur as its food source to avoid a mix-up.
- It is unknown which dinosaur the sample contains. It would be impossible to tell which "species" it is, because the DNA sequences would fit somewhere between that of birds and crocodiles. The book does address this, stating that they "just grow it and find out", to mathematician and chaos theorist Ian Malcolm's annoyance.
- The dinosaur DNA has to be correct (it has to contain every chromosome) and should contain no sequence gaps. The book did address this issue, however, and had the scientists use frog DNA to compensate for the gaps in the dinosaur DNA. However, this causes a problem, as the dinosaurs are then able to change sex (as the frogs from which the DNA was obtained were able to do) and reproduce, thus furthering the problems leading to the park's collapse.
- The DNA is mixed with mosquito, bacterial, and viral DNA. Although PCR is very specific, it is sensitive to contaminations, and if the wrong primers are used, it will also amplify the other DNA.
- Because DNA is broken down by nucleases in the mosquito gut, the mosquito would have to be preserved immediately after feeding; this would be problematic for the park's scientists, although it would explain the lack of mass contamination in the individual samples.
Furthermore, in the fossilization process, molecules are altered. Nevertheless, amber is the best preservative, because organic material is preserved. But DNA cannot survive completely without gaps for tens or hundreds of millions of years.
Tens of thousands of DNA base pairs were recently sequenced from 40,000-year-old skeletal remains of cave bears without using PCR, establishing that, in principle, large-scale genomic sequencing of fossilized remains is possible. Of course, the remains used in this study are orders of magnitude younger than anything from the dinosaur era, and the technique might not extend to those creatures.
In the book the gaps in the DNA are filled by hybridizing the DNA with either bird, lizard, or frog DNA. In the movie, only frog DNA is used. This is extremely difficult, as one would need to know which dinosaur genes are homologous with frog genes. The use of frog genes was a plot device, to allow some females to change sex and breed nevertheless (although natural sex change is also possible in some more advanced vertebrates).
The next step would be bringing the DNA strands to expression. For that, one would need to inject the dinosaur DNA into the nucleus of a fertilized egg cell of a close relative of dinosaurs (birds or crocodiles, not frogs). This technique is based on reproductive cloning, which was used to clone Dolly. In the movie, ostrich eggs are used for this purpose. However, the development of an embryo is regulated by hormones in the egg/uterus and the environment. These (bird or crocodilian) hormones need to have the same effect as their original dinosaurian counterparts. For that, they have to be able to recognize particular pieces of dinosaur DNA, a currently impossible task. New research in plastics, however, has allowed for the creation of synthetic eggs to nurture embryos through their development regardless of species (this technique, or one similar to it, was used in the book). Extra hormones are needed from the original parent specimen, however, or constructed precisely from using the genome in order for the embryo to flourish.
[edit] Further reading
The Science of Jurassic Park and The Lost World. Or How to Build a Dinosaur. Rob DeSalle and David Lindley. BasicBooks, New York, 1997. xxix, 194 pp., illus. $18 or C$25.50. ISBN 0-465-07379-4.
[edit] References
- Cano R.J., Poinar H.N., Pieniazek N.J., Acra A., Poinar G.O. Jr. (1993). Amplification and Sequencing of DNA from a 120–135-Million-Year-Old Weevil. Nature, 363:536–538
- Weaver, R. F. (2002). Molecular Biology. McGraw-Hill, New York, p. 76. ISBN 0-07-234517-9
- Noonan, J.P., et al. Genomic sequencing of Pleistocene cave bears. Science 309(5734):597-9, July 2005.
