Paleoneurobiology is the study of brain evolution by analysis of brain endocasts to determine endocranial traits and volumes. Considered a subdivision of neuroscience, paleoneurobiology combines techniques from other fields of study including paleontology and archaeology. It reveals specific insight concerning human evolution. The cranium is unique in that it grows in response to the growth of brain tissue rather than genetic guidance, as is the case with bones that support movement. Fossil skulls and their endocasts can be compared to each other, to the skulls and fossils of recently deceased individuals, and even compared to those of other species to make inferences about functional anatomy, physiology and phylogeny. Paleoneurobiology is in large part influenced by developments in neuroscience as a whole; without substantial knowledge about current functionality, it would be impossible to make inferences about the functionality of ancient brains. Hominid paleoneurobiology refers specifically to the study of brain evolution by directly examining the fossil record of humans and their closest hominid relatives (defined as species more closely related to humans than chimpanzees). Paleoneurobiologists analyze endocasts that reproduce details of the external morphology of brains that have been imprinted on the internal surfaces of skulls.
History Humans have had a long interest in the brain and its functions. The first recorded study of the brain and its functions was from a papyrus text written by the ancient Egyptians during the 17th century BCE. The document details 48 medical ailments and makes references to how to deal with head wounds. Much later in the 6th century BCE the ancient Greeks began to focus on studies of the brain and the relationship between the optic nerve and the brain. Studies of brain evolution, however, did not come about until much later in human history. Comparative anatomy began its emergence in the latter part of the 19th century. Two main views of life sprung forth; rationalism and transcendentalism. These formed the basis for the thought of scientists in this period. Georges Cuvier and Étienne Geoffroy St. Hilaire were leaders in the new field of comparative anatomy. Cuvier believed in the ability to create a functional morphology based simply on empirical evidence. He stressed function of the organ must coincide with its form. Geoffroy, in contrast, put a heavy emphasis on intuition as a method of understanding. His thought was based on two principles: the principle of connections and the principle of unity of plan. Geoffroy was one of the first to look for homologies in organs across species, though he believed that this was evidence of a universal plan rather than descent with modification. The late part of the 19th century in comparative anatomy was heavily influenced by the work of Charles Darwin in the On the Origin of Species in 1859. This work completely changed the views of comparative anatomists. Within eight years of Darwin's release of the Origin of Species, his views on descent from a common ancestor were widely accepted. This led to a shift in trying to understand how different parts of the brain evolved. The next major innovation that helped to bring about paleoneurobiology was the microscope. Although the microscope was invented in the 17th century, it was only used in biology in the beginning in the late 19th century. The techniques of observing brain cells under a microscope took a long time to refine. In 1873, with this tool in hand, Camillo Golgi began to cellularly detail the brain and employ techniques to perfect axonal microscoping. Ludwig Edinger took advantage of this and came up with a new branch of anatomy called comparative neuroanatomy. Edinger held that vertebrates evolved in a linear progressive series. He also thought that changes in the brain were based on a series of additions and differentiations and that the most highly, complex brains were those that were the most encephalized. The period of 1885-1935 was an explosion of ideas in comparative neuroanatomy. This era culminated in the publication of "The Comparative Anatomy of the Nervous System" by Arienns, Kappers, Huber, and Cosby. This paper influenced Tilly Edinger and she later became the founder of paleoneurobiology.
Tilly Edinger
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