Hierarchies in the energy budget: Thyroid hormones and the evolution of human life history patterns

Abstract

The evolution of human life history characteristics required dramatic shifts in energy allocation mechanisms compared with our primate ancestors. Thyroid hormones, such as thyroxine (T4) and triiodothyronine (T3), are sensitive to energy balance, and are significant determinants for both tissue‐specific and whole‐body metabolic rate. Thus, thyroid hormones are in part responsible for setting the body's overall energy budget and likely played an important role in the evolution of human life history patterns. We propose that the dynamics of mammalian T3 production, uptake, and action have evolved so that energy allocation prioritizes the high demands of brain development and functioning, often at the expense of growth and reproduction. This paper explores the role of thyroid hormone dynamics in the evolution of human encephalization, prolonged childhood and adolescence, long lifespans, reproduction, and human aging.

The Body’s Energy Requirement; General Considerations

“…The measurement of the basal metabolism is done by putting the body in a state of total physical rest, at least 12 hours after eating, in muscle relaxation for 30-60 minutes, in convenient microclimate conditions. It is considered that one calorie per kilogram of body weight per hour is sufficient to ensure basal metabolism in an adult (Levy, & Bribiescas, 2023).…”

Sequential emergence and contraction of epithelial subtypes in the prenatal human choroid plexus revealed by a stem cell model

“…Notably, many of these rely on CPECs for their implementation in the brain. These adaptations include the thyroid hormone (TH) system, which also co-evolved with human encephalization 92 ; the basal metabolic rate 93 regulated by TH 94 ; and the TH carrier and distributor system 95 , including TTR 96,97 , the most abundant CPEC product 11 whose expression is enriched in type 1 and type 1a CPECs (Fig. 4C).…”