Recent research projects led by Muhammad Spocter, Ph.D., associate professor of anatomy, share a theme: How has domestication affected the mammalian brain?
“The domestication of animals marked a major transition in human prehistory, forever changing the way in which humans interact with other animals, while at the same time dramatically affecting the biology of these target species,” he says. “Domestic animals have a number of striking differences from their wild type ancestors, the most obvious changes being differences in coat color, reproductive cycle and changes toward less fearful behavior toward humans.
“The brains of domesticated animals have also changed, and this provides us with a unique opportunity to better understand relative size and organization differences in the brain and their functional significance as well as provide insight into the evolutionary mechanisms which govern brain expansion,” he adds. “This helps us answer questions about how quickly brains evolve and what components within the brain are more susceptible to changes under the influence of domestication.”
Two of his latest investigations into this topic have been accepted for publication in scientific journals. The first, “Scaling of the corpus callosum in wild and domesticated canids: insights into the domesticated brain,” has been published online in the Journal of Comparative Neurology, the oldest journal in neuroscience standing – first published in 1891 – and one of the most rigorous in the field.
The paper compares the corpus callosum, a bundle of white matter fibers that connects the two hemispheres of the brain in several dog-related species. It sheds light on whether the corpus callosum is affected by domestication differentially or strictly in coordination with changes in brain size.
“This research provides the first evidence showing that domestic dogs have a relatively expanded and variable set of fibers connecting to the prefrontal region of their brain,” Spocter explains. “We believe the expansion of these connections has helped to support some of the complex behavior observed in domestic dogs, such as their ability to understand human communicative cues, and provides much needed data on how the impact of domestication and artificial selection affects the mammalian brain.”
A second paper, “Neuropil distribution in the anterior cingulate and occipital cortex of artiodactyls,” has been accepted for publication in the Anatomical Record.
“It also looks at a measure of connectivity – the neuropil space – and demonstrates clear differences in cellular organization between brain regions in even-toed hoofed animals, including domestic sheep, pigs and goats,” Spocter says.
He and his colleagues focused on these animals’ cingulate cortex, involved in social behavior, and the visual cortex, involved in visual processing. They found that 1) across artiodactyls, the cingulate had a lot more connectivity than the visual cortex; 2) the connectivity in the cingulate gradually increases as the animal matures; and 3) this increased pattern of connectivity coincides with known behavioral changes among artiodactyls as they undergo periods of increased social learning.
“Several earlier studies have shown that many herbivores, domesticated animals included, feed in mixed generational groups, where information can be passed from experienced group members to inexperienced members – for example, from mother to her offspring. It has been shown that this allows the offspring to avoid the risks with learning from trial and error,” Spocter says. “For example, ewes which have learned to avoid foods that cause digestive distress, also have lambs that learn to avoid the same food sources much sooner than lambs raised without a mother. Our data suggests that changes in the underlying connectivity of the cingulate cortex likely supports these changes in foraging behavior.
“I think this work is significant given that artiodactyls are understudied in general, and there is an inherent bias to ignore evidence of behavioral or neuroanatomical complexity in these animals. This is probably because so many of these animals contribute to our food source, and I think most of us don’t like thinking of our food as having complex social lives before they end up on our plates,” he says.
Spocter adds that that these investigations align well with the mission of his Evolving Brain Laboratory, housed in DMU’s anatomy department, as it aims to explore the diversity in neural architecture in not only charismatic, large-brained species but also in indigenous and domestic animals that are understudied “and are part of the Iowan landscape.” These and related research efforts could provide unique insight into the human brain and the course of human evolution. Spocter explains that all domesticated species – humans included – have undergone reductions in brain size, but it is important to separate the question of size from complexity.
“When it comes to brains, size isn’t everything,” he says.
He makes an analogy to record albums, which might hold on average 12 tracks, in comparison to the much-smaller MP3 players, which can hold thousands of songs. “If you focused solely on size, it would seem that the record player is more complex than your iPod, but if you looked at the amount of information stored on each, it’s clear that the MP3 player is more complex, in part due to the refining of the underlying structures,” he says. “This is true for brains as well. It’s not just about whole brain/brain component size. We need to also understand the complexity of the underlying connections. For example, the recent discovery of a unique brain cell, the Rosehip neuron, only found in humans (and likely in apes as well), highlights the fact that brains are not equal and that a preoccupation with reducing everything to simplistic mouse or fruit fly models is unlikely to help us fully address questions concerning human brain function or dysfunction. In our laboratory we look to embrace diversity in architecture and use a neuroethological and evolutionary framework to contextualize our comparisons and ask what is unique about each species and how do any of these natural behaviors parallel that observed in humans.”
Spocter’s colleagues on this brainy research included international collaborators as well as other DMU faculty members, anatomy research assistant Kathleen Bitterman and students. For the published research on the canine brains, they included Rachel Dunn, Ph.D., assistant professor of anatomy; Ashraf Uddin, a 2018 graduate of DMU’s osteopathic medical program; and Jordan Haas, a fourth-year student in the program. For the article on the artiodactyl brains, his collaborators included Dunn; Simon Geletta, Ph.D., professor of public health; Jeremiah Fairbanks, a 2017 osteopathic graduate; and Lisa Locey, a third-year student in the program.