In order to understand the reasons for the incidents of cardiovascular disease in contemporary society, we must understand the situations and selective pressures during the late Paleolithic era.
So influential was this period in the scheme of human evolution, that it is believed that 95% of human biology was naturally selected during this 40,000 years (Chakravarthy and Booth, 2004). In addition, to appreciate the reason for our current physiology, it is vital to appreciate our physical environment of evolutionary adaptiveness (Danziger, 2001), for this understanding forms the basis of evolutionary medicine. Survival of pre-humans was primarily reliant on the procurement of food. Due to the nature of a hunter-gatherer population, a by-product of this food procurement was physical activity. The inconsistency of food supply led to a hunter-gatherer’s diet being characterised by periods of feast and famine, and contrasting periods of high intensity physical activity and rest (Chakravarthy and Booth, 2004). The food available to these populations (though inconsistent) comprised of animals caught via hunting, and uncultivated plant foods from gathering, with meals often comprising high volumes of gorged food. Food procurement equated to three to five hours of physical activity daily spent in sustained activity, at a moderate to high level of intensity (Cordain et al., 1997). Considering the above situations, the goal of the hunter-gatherer’s lifestyle was to maximize energy intake and minimise energy output, on its own a contraindication of cardiovascular disease, while in reality, the outcome of the selective pressures resulted in a low energy intake and a high output (UCLA, 2004), creating an ideal cardiovascular disease preventative environment.
The selective pressures of the late Paleolithic era selected the metabolic characteristics we possess today, metabolic pathways that oscillate to support and coincide with cycles of feast-famine and of physical activity-rest (Chakravarthy and Booth, 2004). It is also proposed by Chakravarthy and Booth (2004), that it is the feast-famine and physical activity-rest phases that drive these pathways, and that the selection of a Thrifty genotype is molded by the cycling of fuel stores, blood insulin, insulin sensitivity and metabolic regulatory proteins. Neel (1961), who formulated the ‘Thrifty Gene Hypothesis’ defined a thrifty genotype as “…being exceptionally efficient in the intake and/or utilization of food.” He stated that the selective pressures, as previously described, favoured a Thrifty genotype which allows individuals to rely on larger energy reserves to maintain homeostasis. Naber et al. (2003) have identified this genotype as a GNB3 gene polymorphism (Naber, Erbel and Siffert, 2003), though this remains to be proven. I propose that the ability to store increased levels of triglycerides maintained the individuals during a famine, and the increased glycogen storage increased the ability to procure food. Thus the gene increased in frequency due to Natural Selection caused by diet and exercise and became apparent in larger numbers of the population, where it remains in contemporary Homo sapiens.
At the end of the Paleolithic era, a series of events occurred which would forever change the path of humankind, and ultimately lead to the prevalence of cardiovascular disease apparent today. By tracing the origins of humanity using fossil records (Cordain, Gotshall and Eaton, 1997), we are able to determine this chapter in our history where the primary method of adaptation changed from biological to cultural evolution, leading to the pathogenic nature of the Thrifty gene today. From fossil records, we can ascertain that our ancestors 40,000 years ago would be virtually inseparable in appearance to contemporary humans (Cordain, Gotshall and Eaton, 1997). “Socially we are a people of the 21st century, but genetically we remain citizens of the Palaeolithic era.” (O’Keefe and Cordain, 2004). These ‘Cro-Magnon people’ lived primarily in Europe (Relethford, 2000), and although the human species has now filled most niches on Earth, the basic appearance remains constant. This lends evidence to the fact that we have pinpointed the moment in our history where we began to evolve culturally to our environment, rather than evolving biologically as a product of natural selection. In this epoch pre-humans began to control the necessities of life. We no longer had as great a need for selection of favourable biological traits. “This does not mean that biological evolution ended. On the contrary, it remained as important as ever. It simply altered direction. The emerging human body evolved to fit its ecological niche, to survive as a living creature. The emerging human mind now evolved to fit its cultural niche, to survive as a social creature.” (Leakey and Leakey, 1978). With the social evolution came a change in lifestyle; exercise and diet.
