Human Adaptation to Deep Space Environment: An Evolutionary Perspective of the Foreseen Interplanetary Exploration

Abstract

Long-term and deep space exploration is a prevailing dream that is becoming a reality. Is that so? The answer to this question depends on how the main actors of space exploration, i.e., politicians, scientists, and engineers, define "long-term" and the ultimate goals of the current space programs. Presently, long-term refers to few months or years, which is equivalent to the time necessary for a manned mission to reach another planet and return to Earth. Such a space mission is a tremendous scientific challenge associated with multidisciplinary issues spanning from technology to medicine biology, social, and psychological science. It has been a priority of the main westernized societies that has attracted the brightest and most innovative scientific minds since World War II. At first the stakes were mainly political in order to demonstrate to other countries power and strength. It progressively became a scientific motivation to uncover the secrets of the Universe and life's origin, and potentially to find traces of distant life. More recently, a desire to colonize space and exploit resources on other planets has emerged as a new dream. Although the journey to Mars is still a prospective and traveling in deep space a further elusive goal, one can question the ultimate implications of deep space exploration over the long-term.

Prolonged Exposure to Microgravity Reduces Cardiac Contractility and Initiates Remodeling in Drosophila

“…However, future space exploration efforts by government and commercial ventures are focused on missions to the moon, asteroids, and Mars, and those explorations will require astronauts to spend many months and perhaps years in altered gravity. Thus, information on how prolonged microgravity exposure affects different organ systems will be critical to the success of those efforts ( Criscuolo et al, 2020 ; Prasad et al, 2020 ). It is likely that, at the cellular level, there are underlying and conserved responses to altered gravity that are shared between organisms.…”

Microbial Pathogenicity in Space

“…Our understanding of microbial interactions and impact is being pushed into new frontiers, extending beyond the confines of our own planet. Space exploration is witnessing increasingly longer crewed missions, with astronauts expected to spend extended time in spaceflights, especially with planned missions to the Moon and Mars, which raises several challenges and potential hazards [ 2 , 3 , 4 , 5 , 6 ].…”

“…A significant research emphasis has been placed on assessing physiological and phenotypic changes of microbes (and astronauts) when exposed to the space environment or space-like conditions, as portrayed by Criscuolo et al [ 5 ]. As stated by these authors, deep space exploration might become longer, and the exposure to the space environment will lead to adaptations relevant to fields such as evolutionary biology and ecology [ 5 ]. Nevertheless, information on multiple combined stressors or on complex microbial communities is still lacking.…”

“…As discussed for microbes, humans are also exposed to a variety of hostile environmental changes during spaceflight. Those include variations in gravity (from microgravity to hyper-gravity periods, which occur during launching and landing), acute and chronic exposure to radiation, and psychological stress, as well as loss of nycthemeral cycles and perturbation of normal circadian rhythms, exposure to extreme temperatures, variable magnetic fields, and hypercapnic conditions ([ 5 , 17 , 113 , 114 , 115 ]). In more prolonged missions, long-term isolation impairs sleep, mood, and alertness, compromises muscular strength and endocrine physiology, induces changes in hormone levels and metabolism [ 17 , 116 ], and causes microbiome shifts [ 9 ].…”

“…Microgravity is the stressor considered as responsible for the higher number of body changes. These include loss of bone and irreversible bone resorption, loss of muscle mass, cardiovascular deconditioning and dysfunction, impaired exercise capacity, altered neurovestibular perception, ocular changes, immune-deficiency, alterations of peripheral metabolism) [ 5 , 9 , 120 ]. Altered gravity affects biological processes that respond to normal gravity, causing abnormal physiological responses.…”