30 Adult Hippocampal Neurogenesis in Natural Populations of Mammals

This chapter is based on the premise that if we are to acquire a deep understanding of adult neurogenesis—what it is selected for (i.e., its functional and adaptive significance), what causes it to go up or down (e.g., species constraints, reproductive hormones, seasonality, stress, and environmental conditions), and why it declines with age—the research must ultimately be grounded on an evolutionary and ecological foundation. The aphorism of Dobzansky (1973) is particularly apropos: “Nothing in biology makes sense, except in the light of evolution.” Thus, simply focusing on humans and those laboratory species we select for will not be sufficient to crack this enigma. Such a deep understanding may also aid in ameliorating debilitating aspects of the human condition after injury or in disease. This chapter advocates for studies that deal with animals that live out their lives in the context of what they were actually selected to do. Given the paucity of studies from nature, it raises more questions than it answers. It focuses largely on mammals. The formation of new neurons in adult animals is a highly conserved trait in vertebrates, occurring in all groups, from fish to mammals in various brain regions. It is linked to a diversity of life history traits such as lifelong body growth in fishes and rats and seasonal variation in song control nuclei in birds (Lindsey and Tropepe 2006). In mammals, adult neurogenesis occurs physiologically in two germinal areas: the subventricular zone (SVZ), which lies adjacent to the lateral wall of...