“If You Give a Mouse A Human Brain: How Neural Chimeroids Reshape Brain Exceptionalism and Recall Mytho-Kinship”

Our genetics, endocrine system, reproductive system, and fundamental social behaviors are all similar enough to those of other-than-human animals that evolutionary relatives such as mice, rats, monkeys, and dogs have long served as effective proxies for human bodies in lab research, including studies on emotional states. These compatibilities go beyond testing or observation—with advancements in gene editing and surgical techniques, we can effectively produce biological chimerism through xenotransplantation, replacing malfunctioning human organs such as kidneys or heart valves with their nonhuman counterparts.

Unlike other organs, the human brain itself has remained ontologically isolated—practically sacred as an embodied concept—within the value system of industrialized modern science. While manipulation of brain chemistry has been tested on model species, until recently, we have not dared to cross the biological boundary of merging synapses. However, with the creation of neural chimeroids, that is no longer the case. The human brain—the gold standard of cognition and the biological center of human supremacy—can now be integrated into nonhuman animals, and potentially, one day, vice versa. 

The explicit aims of this new biomedical technology are to study brain development, neurodevelopmental disorders, and neurological diseases; to gather data on how brain cells interact with one another during development; to provide a more effective model species to check for drug toxicity; and to eventually replace damaged brain tissue in humans. However, this development in neural relationality does much more than just provide a more effective proxy—it disrupts the prevailing value systems and ontological categories present in contemporary science. First, our understanding of these chimeras’ cognition is underdeveloped, so issues of consent and metrics for limiting suffering are particularly urgent. Yet, beyond practical concerns, deeper engagement with the metaphysical implications of this technology is equally critical to any meaningful consideration of suffering. To date, neuroscience has adhered to a functional materialist approach to life with a hierarchy of intelligence that positions human brains at the teleological peak of evolution. With the advent of neural chimeras, this framework can no longer be justified from a biological standpoint. If the very organ presumed to define our uniqueness can be merged with the brains of other species, then the assumption of human supremacy is not scientific but philosophical. By its very existence, this new lifeform reshapes notions of kinship while recalling the ethical frameworks present in folk metaphysics found in comparative mythology dealing with chimeric creatures. This places the neural chimeroid squarely in the realm of religious studies.

Cultural mythologies have pervasively featured chimeras, and the sanctity of the Homo sapien brain has been nebulous in many practices and renderings. Human heads, presumably housing human brains, have frequently been attached to other-than-human bodies—from fantastic creatures such as the Chinese Zhulong dragon to fellow mammals like the Greek Centaur. Many scholars of religion and folklore have already argued that chimeras challenge anthropocentrism—they are sites of relationality, functioning like connective webs as understood through kinship theory. Yet, these interspecies transhumans are more than powerful mediator figures; they trouble the demarcation of the human brain as unique. In the very act of fusing synapses, interspecies neural chimeroids do the same as their mythological forebears. 

In this paper, I present the research methodologies and experimental reasoning involved in the creation of neural chimeroids. I then explore the complex ethical anxieties surrounding this new technology by employing a biopolitical lens in conjunction with kinship theory and comparative mythological analysis. Although cerebral organoids would also be relevant, I focus on neural chimeroids generated in two ways. The first (blastocyst complementation) involves implanting human stem cells into nonhuman animals during the embryonic stage, then manipulating those cells to develop into neurons. The second method (interspecies human neuron chimerism) involves grafting human cerebral organoids directly into the damaged brains of adult model species—such as mice or monkeys. 

My case studies include the Wilson et al 2022 paper which detailed their success in transplanting human cortical organoids—or functioning human synapses— into the retrosplenial cortex of fully-grown lab mice. Another case study features Yale University’s Eugene Redmond’s use of African Green monkeys in his lab. Whether the behavior or lifespan of these chimeric creatures was altered by the presence of human neurons has not been mentioned in the papers I’ve analyzed thus far. That may seem like an oversight to more than just the average sci-fi reader, but it is, in fact, a gatekeeping function; it forces readers to ignore the phenomenology of our evolutionary kin by denying access to insights into their lives as chimeric creatures. 

Redmond expressed that as his team inserted only “8 to 10 million human cells in a brain that maybe has 20 to 40 billion cells,” it would be “extremely unlikely” that his monkeys would be humanized. Likewise, Lorenz Studor, the founding director for the Center for Stem Cell Biology, stated, “we do not want to create these fantasy creatures that people imagine from Greek mythology…people are, for example, afraid to get a human brain in a mouse. You can easily point out that the human brain is three pounds in size. The mouse’s [brain] is twenty grams.” But, let’s say we ask that basic question: is there a human brain in that mouse? Unless human brains come in percentages, the answer would be unequivocally ‘yes.’ So, what does “humanized” mean? Not to mention that the racist and ableist history of ranking humanness based on biological traits is well documented; so, is a hierarchy of humanization still appropriate? 

We live in a field of evolutionary similarities and differences, reflective of many mythological contexts. Neural chimeroids emphasize this—they show that on a biological level, our brains are not exceptional. They necessitate not only a reexamination of consent and capacity for suffering, but demand a reconsideration of brain-exceptionalism in hegemonic practices in the biological sciences. The choice to etymologically merge these intermediary lab subjects with the great chimeras of myth forces us to further interrogate the ontologies underpinning prevailing power dynamics between humans and our nonhuman kin.