The term model is unfortunately used very inappropriately by many scientists. (See It Turns Out Animal Models Really Aren't Predictive.) I have previously discussed the nine ways animals can be used in science and research as it is important to understand that categorizing animal use allows us to critically examine claims made about such uses specifically and to compare and contrast these findings with more global sweeping generalizations about animal models. Many times in this blog and elsewhere I have pointed out that animals can be successfully used in various scientific activities but that animal models are not predictive for human response to drugs and disease. Conflating the various uses of animal models is a trick used by vivisection activists in order to justify the repeated failures of animal models in human-relevant drug and disease research. Two news items illustrate why being precise is important.
The fact that genes have various functions and that these functions vary among phyla and even species is universally acknowledged. Also acknowledged is the fact that different genes can be used to result in the same outcome. A related facet of evolution is illustrated by the discovery of “signaling centers” that regulate the development of the vertebrate brain, in the acorn worm (Saccoglossus kowalevskii), an invertebrate. These signaling centers are present in vertebrates but not sea squirts or lancelets, which are the invertebrates most closely related to vertebrates. The signaling centers determine where the forebrain, midbrain, and hindbrain are located in vertebrates. These brain structures are not present in worms, therefore finding the signaling centers in the worms was a surprise. Also surprising was the fact that the signaling centers result in the presence of nerve cells in essentially the same location, relatively speaking, in the worm’s proboscis. This means these genetic programs interact similarly to the way they interact in vertebrates. The fact that our closer invertebrate relatives, the sea squirts and lancelets, do not have these signaling centers means they were lost over evolutionary time.
Ariel Pani, one of the authors stated: “And one of the broad implications is that weird, squishy marine animals can be very informative in terms of understanding the evolution of vertebrate development and genetics in a way that you wouldn't expect.” I completely agree with this statement. If you want to learn about comparative anatomy then you must study different species. This is tautological. The article appears in Nature (Pani et al. 2012) and can found here.
Compare and contrast the comparative research on acorn worms with the following, also involving invertebrates.
A press release from the University of Missouri-Columbia announces: “Sex-deprived fruit flies' alcohol preference could uncover answers for human addictions.” Apparently, male fruit flies (Drosophila melanogaster) that are rejected by females seek solace in alcoholic beverages. Troy Zars of the University of Missouri-Columbia commented on the article in Science stating: “Identifying the molecular and genetic mechanisms controlling the demand for reward in fruit flies could potentially influence our understanding of drug and alcohol abuse in humans, since previous studies have detailed similarities between signaling pathways in fruit flies and mammals.” Now, I do not doubt that genes influence behavior nor do I doubt that these genes overlap among species. But alcoholism is a complicated, multifactorial, socially-related disorder that occurs in a complex system, namely humans. Therefore, suggesting that research in invertebrates “could uncover answers for human addictions” is simply beyond the pale. Once again we see people with a vested interest in something, in this case fly research, greatly exaggerating the results of similar research and completely ignoring the science of complex systems not to mention the fact that alcoholism has a strong social component. I have no ethical objections to research using fruit flies (at least I didn’t until I learned they seek out alcohol after being dismissed by the opposite sex, now I wonder if the little critters might not be sentient), but suggesting a one-to-one correspondence between the results from fruit flies and alcoholism in humans is just not good science.
Comparative research is just that—comparative. It takes two or more species. However, using animal models to predict human response to drugs and disease is not supported by the empirical evidence and is prohibited in theory vis-à-vis evolutionary biology and complexity. Nevertheless, the prediction claim is how animal-based research is sold to society and this fly research is yet another such an example. I can understand researchers that use nonhuman primates, cats, dogs, and even rodents lying about their research. They want society to continue to allow, and fund, their research and society would not do so if they understood how poorly predictive animal models really are. But fly researchers!?! Seriously? Come on guys. Who is outside your building protesting against fly research? If you want to convince congress that funding fly research is important, try explaining to society why such research is important instead of spinning nonsense.
Animal models can be used in comparative research as well as for a heuristic and the above research is an example of such use. But the claims being made for the barfly research far outstrip the reality.
Pani, Ariel M., Erin E. Mullarkey, Jochanan Aronowicz, Stavroula Assimacopoulos, Elizabeth A. Grove, and Christopher J. Lowe. 2012. Ancient deuterostome origins of vertebrate brain signalling centres. Nature 483 (7389):289-294.