The Impact of Early Human Migration on Brown Adipose Tissue Evolution and Its Relevance to the Modern Obesity Pandemic

Abstract

Genetic factors are believed to be primarily responsible for obesity; however, an understanding of how genes for obesity have become so prevalent in modern society has proved elusive. Several theories have attempted to explain the genetic basis for obesity, but none of these appear to factor in the interethnic variation in obesity. Emerging evidence is increasingly pointing to a link between reduced basal metabolism and ineffective brown adipose tissue (BAT) thermogenesis. In fact, BAT presence and function are strongly correlated with metabolic rates and directly influence obesity susceptibility. My colleagues and I recently theorized that ancestral exposure to cold necessitated the evolution of enhanced BAT thermogenesis, which, with today’s hypercaloric and sedentary lifestyle, becomes advantageous, because thermogenesis is energetically wasteful, raising basal metabolism and burning excess calories. The opposite may be true for the descendants of heat-adapted populations. This review further reconciles global evolutionary climatic exposures with obesity demographics to understand the genetic basis for the obesity pandemic, and new insights from the most recent studies are provided, including those assessing archaic human admixture. Key genetic variants influencing BAT thermogenesis are outlined that have also been linked with climatic exposure to cold and appear to support the theory that evolutionary factors relevant to climate may have shaped the modern obesity pandemic.

Introductory Chapter: Unbearable Burden of the Diseases - Obesity

“…The brown adipocytes are multilocular and contain less lipid. [19]. Recently, it has been shown that the brown adipose tissue could be increased with the catecholamine discharge.…”

“…Biologically, humans are prone to conserve body fat as a defense mechanism in case of starvation and famine. The theory of "thrifty gene" claimed that human genes were predisposed to accumulate adipose tissue for use in case of energy requirement [1,11,19]. This mechanism was a key factor for survival once.…”

Obesity and climate adaptation

“…This could partially explain why certain ancestral groups within the same country, e.g. European Americans or East Asian Americans, have a lower obesity burden 5 . In fact, there is evidence of selection by climate across the genome, 6 and specifically in genes related to the non-shivering thermogenesis of brown adipose tissue (BAT) like those encoding the uncoupling proteins (i.e.…”

“…Evolutionary principles may inform the prevention and treatment of obesity via the development of tailored lifestyle guidelines. For example, caloric intake recommendations may want to take differences in RMR across ancestral populations into account 5 . Thus, taking an evolutionary perspective to the study of obesity may shed light on the role of evolutionary trade-offs and mismatches in both clinical care and global health.…”

Bone Density and Genomic Analysis Unfold Cold Adaptation Mechanisms of Extinct Inhabitants of Tierra Del Fuego

“…Subsequently to the dispersal of Homo sapiens out of Africa during the Paleolithic [1], human populations required adaptations to diverse climatic conditions [2] achieved through morphological and cultural adjustments and metabolic mutations [3], such as brown adipose tissue (BAT) upregulation in cold climates [4]. The interest in understanding the mechanisms of cold adaptation comes both from obvious anthropological and evolutionary implications, and from theories that attribute to populations with higher BAT activity an increased resistance to obesity and diabetes [5]. When Europeans reached Tierra del Fuego in 1520, it was inhabited by different populations (mostly named Yamana, Alacaluf and Ona) generally grouped under the term Fuegians, today extinct [6].…”