Beyond Earth (ATWG) - Chapter 11 - Evolutionary Psychology and Its Implications for Humans in Space by S. Bell and D Strongin

From The Space Library

Chapter 11

Evolutionary Psychology and Its Implications for Humans in Space

By Sherry E. Bell and Dawn L. Strongin

As the human habitat changes, so will its control center—the human brain.

Our view of the future of humans is optimistic. Humans have evolved and will continue to do so, and humans in space are likely to evolve in ways that differ from those who are Earth-based. This chapter examines the underpinnings and extrapolates some expected evolutionary changes. It is meant as a thought-provoking piece.

Innovations in physics and engineering have made space travel a possibility. The relative time and energy allotted to propelling out of Earth's atmosphere has far outweighed emphasis placed on studying the effects of prolonged weightlessness and hypergravity on the human traveler. With the exception of moon travel, space flight studies have been limited to low Earth orbit, and those not exceeding a little over six months. Thus, our views on the psychological and physiological effects of long-duration orbital flights and non-returning spacefarers are purely conjecture at this point.

Introduction to Evolutionary Psychology

The basic premise of evolutionary psychology is that evolutionary pressures effect change in all living individuals. Larsen & Buss, 2005 (9) describe this as: "The basic elements of the evolutionary perspective apply to all forms of life on earth, from slime molds to people" (p. 237). The research goal is to discover and understand the design of the human mind by understanding the evolved properties of the nervous system, especially those of humans, which are most malleable to internal and external environmental stressors (Cosmides & Tooby, 1997, (4)). Evolutionary psychologists

attempt to find the "functional mesh" between adaptive problems posed by the environment and inherited architectural changes within organisms designed to solve these problems (Cosmides, Tooby & Barkow, 1992 (5); Cosmides & Tooby, 1997 (4)).

Because all living tissue is functionally organized and is a product of natural selection, a major assumption of evolutionary psychology is that the nervous system, too, is functionally organized to serve survival and reproductive needs, and is best understood from an evolutionary perspective (Cosmides, Tooby & Barkow, 1992 (5)). Thus, a major lesson of evolutionary psychology is that if you want to understand the brain, look deeply at the environment of our ancestors as focused through the lens of reproduction, and if the presumptions of evolutionary psychology are correct, the structure of our brains should closely reflect the reproductive ecology of our ancestors (Buss, 1999 (2)).

One way to think about the evolution of the human brain is by examining its increasing level of power over the environment. The primitive nervous system evolved over millions of years, permitting humans to become the most adaptable organism on Earth — adapting to, improving, and enhancing a tremendous variety of living conditions from wind-swept deserts to icy snow caps. In the process, "human beings have caused greater changes on earth in 10,000 years than all other living things in 3 billion years. This remarkable dominance is related to the development of the brain from the minute cerebrum of simple animals to the complex organ of about 1350 grams in man" (Sarnat & Netsky, 1981, p. 279 (13)).

Our hominid ancestors had smaller brains than present day humans. Relative brain size has increased over generations, and changes in its structure are a result of adaptation to the environment. Specifically, the neocortex has grown exponentially compared to its origins, and in fact this bulging mass almost completely occludes the more primitive brainstem. The ability to plan and to think abstractly relies on the development of the neocortex, and complexities in environment can be addressed by complex thought and variability in behavior. The most sophisticated devices our ancestors made are primitive by our standards. They had stone knives and carving tools, and later spears, but we, in contrast, have developed telephones, computers, automobiles, airplanes, rockets, satellites, and a space station, to mention just a few. And of course, humans have traveled to the moon and back. Hence, our abilities to imagine, to reason, and to learn are quite different in degree of those same abilities in our hominid ancestors. Although they could do many of these things, they could not do them with the level of complexity that we now can.

Thus, our present day cultures and institutions, our societies, our very way of life would have been inconceivable for our ancestors, and in much the same manners it is likely that our progeny will be dramatically different from us. Many, for example, will live in space stations, some will live in extraterrestrial space settlements, while yet others will be spacefaring, so we can state that the evolution of the brain's inner space has made outer space accessible.

Humans in Space

On October 4, 1957 the Soviet Union precipitated the space age by sending Sputnik I into orbit. This artificial satellite, no bigger than a basketball and weighing as much as an average man (183 lbs), launched dreams into the reality of space exploration. Four years later, on April 12, 1961, the Soviets sent cosmonaut Yuri Gagarin into space, and virtually every year since then, Soviets or Americans sent humans into space. While the first missions were short-lived, subsequent missions were longer in duration, ranging from a day to over a year.

In August 1961 Russian cosmonaut Titov was the first to spend a full day in space, while the following year American astronaut, John Glenn, was the first to orbit the earth. During the Mercury Program (1961-63), the first six American astronauts in space accumulated less than 54 collective mission hours. In June 1970, Russia's Nilolayev and Sevastyanov spent a record 18 days in space, and in 1971 three Russian cosmonauts worked aboard a space station for 24 days.

During 1972, the longest Apollo mission, Apollo 17, lasted 12 days, 13 hours and 52 minutes. In 1973, American astronauts spent 84 days in space aboard the Skylab. In 1978, two Soviet cosmonauts set a record of 136 days in space, but a year later that endurance record was bested for a total of 175 days in space. The record was broken again in 1982 by Soviets working for seven months on a space station. The Expedition 7 crew lived on the International Space Station for over six months. The longest duration in space was by the cosmonaut Valeri Polyakov, who stayed aboard the Russian space station Mir for 438 consecutive days.

Over the decades, we have learned much from the experiences of cosmonauts and astronauts about the physiological influence of space on human beings. Experiments conducted on Earth and on the International Space Station have provided insights into the effects of weightlessness on the human body, information that is vital to human spaceflight and long-term space travel, as "plans for colonization of the Moon and Mars will move the duration into years and, perhaps one day, into generations" (Griffin, 2005 (7)).

Effects of Gravity

Long-term space travel and multi-generational colonization of planets within and outside our solar system is steadily moving towards becoming a dream materialized, but concerns regarding the psychological and physiological effects of prolonged exposure to microgravity and hypergravity are consequently getting increased attention. As described by Cohen, "gravity shapes life…It defines the character of the nervous system, our reflexes and our bones" (Malcolm Cohen as cited in Shwartz, 2002, para. 7 (14))

Researchers on Earth and the International Space Station have provided a peek into the mechanisms behind these effects, and while the gravitational force on Earth obviously has inconvenient consequences, such as laboring uphill or sagging over-the-hill flesh, the evolution of human physiology has naturally reflected the Earth's gravitational effects.

Microgravity

Orbital spaceflight is not a significant distance from Earth's center, and thus gravity is minimally decreased, creating microgravity. However the astronaut is virtually weightless due to free fall. In other words, the scale used to measure weight and the weight to be measured (the astronaut) are falling (due to gravity) around the Earth's orbit at an identical rate (Turner, 2000 (15)). Gravity remains present but weight is markedly decreased. Therefore the physiological effects studied on the space stations are more accurately described in terms of weightlessness versus lack of gravitational force.

A few days or weeks in microgravity may be uncomfortable, but it is not damaging to the health of astronauts. However, on shorter missions, astronauts have reported severe motion sickness. The vestibular system relies on gravity, so as the head tilts, hair cells in the inner ear are displaced, creating a signal to the brain regarding the head position and balance. When these signals from the vestibular system and the brain are incongruent, an individual feels nausea. However these symptoms abate over time, and astronauts on long-term missions adapt quite readily.

On longer missions, astronauts endure somewhat detrimental effects, such as blood and body fluid shifts, muscular atrophy and bone density loss. Blood pooling is a concern when astronauts have been in microgravity for prolonged periods. Without resistance to gravity, fluids shift from lower extremities to the upper body and face, creating discomfort. When a person stands on Earth, 300 to 800 mL of blood pools to the lower extremities. Standing, or mechanical load, causes muscles in legs to contract, and veins in the abdomen to restrict, forcing blood to circulate back up. Blood pooling is avoided when veins and arteries constrict while the heart rate increases blood flow through one-way valves. However, without gravitational opposition, blood pressure decreases, causing the potential of cerebral ischemia (i.e., blood loss in the brain) and neuronal (i.e., brain cell) death (Pinel, 2005 (10)).

Although rigorous exercise in space prevents lost muscle mass, sustaining bone density requires additional gravitational resistance. Without the appropriate signals precipitated from gravitational force, space-induced bone loss develops. On Earth, bones grow and change shape based on the weight put on them. Resistance to gravitational pull signals gene expression of new bone formation and resorption. Approximately 10% of bone mass is removed and replaced every year for the maintenance of healthy bone. The balance between growth and removal of bone is tipped over a lifetime. Men experience an average of 15% bone loss while women experience an average of 30% loss, mostly after menopause (Turner, 2000 (15)).

Without the signal created from gravitational resistance, bone maintenance is altered. Gene expression signaling the production of bone formation is dramatically reduced with an increase in bone resorption, creating fast bone loss (Wang, 1999 (17)). Astronauts studied under conditions of microgravity lost approximately 1-2% in weight-bearing bones each month in areas such as pelvic bones, lumbar vertebrae and femoral neck (Carmeliet & Boullon, 1999 (3); Grigoriev et al., 1998 (8)). Because bone grows slowly, replacing it takes a long time, creating a serious health risk for those returning to the gravity of Earth (Bloomfield, 2001 (1)). Notably, the upper skeletal regions were either not significantly changed, or there was a positive trend. Thus as the pelvis and legs begin to atrophy, the upper skeletal regions remain intact or increase in density. As long as the space traveler does not return to gravitational force where bone and muscle integrity are required for gravitational resistance, such changes are unimportant.

That said, many space travelers will settle on other planets or return to Earth. Osteoporosis and muscular atrophy resulting from long-term weightlessness will be debilitating when spacefarers are required to build extraterrestrial settlements having gravity that differs from that on earth, or when they return to Earth's gravitational pull. Artificial gravity, whether close to Earth's 1-g or greater, will be an effective countermeasure.

Hypergravity

Hypergravity is gravitational force greater than Earth's. Most of us have experienced the sensation of hyper-gravity. At every county fair can be found a ride in which individuals stand against the interior wall of a circular contraption. As the wall spins faster and faster, the floor gives way, but the individuals are pinned against the wall and do not fall down. This ride is a centrifuge, producing a gravitational pull three times that of Earth. Astronauts currently experience hypergravity at launch (up to 3.2-g) and at reentry (-1.4-g). Due to the short duration of this force, astronauts have had short-term difficulty adapting to increased gravitation, and have experienced loss of consciousness and nausea.

Because body fluid is heavier during hypergravity, the heart must pump faster and harder to push blood to the brain (Vince, 2002 (16)). An experiment conducted by Arthur Hamilton Smith in 1970 (as cited in Regis, 1991) sheds light on this issue. Smith used the Chronic Acceleration Research Laboratory at UC Davis to study the effects of hypergravity on chickens living in 2.5-g. Chickens, like humans, are bipeds with non-bearing limbs (wings). Hundreds of chickens were put into two 18-foot centrifuges for from three to six months, and during this period 23 generations were bred. The findings showed that at the end of the experiment their bones and muscles were bigger and stronger, while their hearts circulated more oxygen than before.

Artificial hypergravity may serve to counteract permanent losses, and may provide a particular advantage for space settlers who require strength and endurance. Conditioning training before launch will provide the time the brain and body need to adapt to the additional gravitational force before living conditions actually change.

As we noted earlier, long-duration exposure to microgravity creates circulatory problems as well as muscular and skeletal atrophy. Managing the effects of hypergravity will be important for those who will return to Earth after a long stay in microgravity, and for those living and working in space settlements on planets with gravity greater than that on Earth. Under those conditions, both the skeletal and muscular systems will need to alter the way they function.

NASA is currently exploring human adaptability to artificial hypergravity by means of exposing humans to centrifuges for prolonged periods of time. It is likely that astronauts living in conditions of hypergravity will develop larger bones and muscles, and will present with increased oxygenation.

The Plastic Brain

In order for we humans to experience sensations, perceptions, thoughts, movement and basic life functions, neurons, or brain cells, communicate with each other. A network of communication develops as pathways become established. The human brain is remarkably malleable, or plastic. Communication among the neurons can develop new patterns based on the brain's experiences, as the brain is shaped by the characteristics of its environment. These changes can take from hours to years.

The developing brain requires specific input to establish appropriate connections and those connections are based on the need to adapt the environment. For example, a child born blind may over-develop other sensory modalities, such as touch and sound. The visual neurons are not needed, so they may be recruited to become part of the network for processing touch and/or sound information, or they may be recruited by both. The consequence of blindness therefore, can be either a more finely tuned tactile or auditory function, or both.

The primary cortex, a region in the brain involved in voluntary movements, is also capable of modification. Neuroimaging techniques show considerable plasticity of the motor cortex. For example, without the use of weight-bearing limbs, the neurons motor originally devoted to lower body motor control are recruited to support the intact upper muscular and skeletal systems.

Muriel Ross at NASA-Ames Research Center (1996) found rapid neuroplasticity in her study of the vestibular system of rats (who are mammals) living in prolonged microgravity on NASA's Space Life Sciences Mission. Her studies included two experiments ranging in duration from nine days to two weeks. As noted earlier, one of the effects of microgravity is the loss of a sense of body orientation and balance due to the gravitational silence in the inner ear. Within 7 to 14 days, the rats regained balance and orientation. Close examination of the rats' brains indicated neuroplasticity, most evidenced by increased synaptic density among the neurons in the associated regions of the brain. Dr. Ross postulated that the resulting formation of new synapses was an attempt by the system to return to an output which was more adaptive in the absence of gravity.

Neuronal plasticity is thus a mechanism which can be used to compensate for lost or reduced function, or to maximize remaining function in the event of brain injury, or to adapt to dramatic environmental changes. The brain can literally modify itself in response to its environment. In their effort to enhance efficiency, neurons can change their basic structure and their connections to other neurons. This neuronal plasticity does not require generations to accomplish, and in fact, changes readily occur within a short time frame. Such changes will occur in humans as well, for, as the human habitat changes, so will its control center—the human brain.

Conclusion

During relatively extended excursions under microgravity, astronauts and cosmonauts began to adapt. Motion sickness abated over time, but detrimental effects such as muscular deterioration, bone density loss, and cardiac insufficiency were pronounced upon returning to Earth's gravity.

Long-duration, and to a lesser extent, shorter exposure to microgravity induce changes in brain organization, and thus sensory and motor function, skeletal muscle and bone maintenance, and cardiovascular efficiency. These changes are appropriate to the immediate environmental requirements and demonstrate human adaptability. In particular, the adaptability of the nervous system is an important principle underlying human evolution, and studies have shown that the brain has undergone neuronal reorganizations in relatively short periods of time as the brain literally restructures itself to meet the demands of the environment.

Dramatic changes in the environment alter the organization of the brain and function of the body.

The morphology of the brain and body literally changes to accommodate the immediate environmental needs. To accommodate environmental changes individuals who live in a permanently weightless environment will develop changes in their cerebral cortex's subserving sensory and motor functions. The vestibular system, no longer receiving gravitational signals necessary for the brain to decipher body position and balance, will alter. Neurons from other sensory modalities may take over these areas. The resultant brain reorganization may therefore increase sensitivity and enhance function of other systems, for examples, the tactile and visual systems might be among those which are altered.

In addition, recall that when the brain does not receive sufficient gravitational information, the gene expression for the preservation of bone density is altered. The brain assumes that bone formation is no longer necessary in the weight-bearing lower extremities, and thus this function is ceased. Astronauts in space have commented that their legs were not necessary, and were in fact, in their way. Taken together, this could mean that the no-longernecessary weight-bearing limbs, i.e., pelvis and legs, might atrophy over time. Perhaps selection pressure will thus act to produce generations of humans who have no legs.

Additional changes are also likely to occur. Weightlessness will also cause changes in genetic expression and neuronal connections in the skeletal and muscular systems. Spaceflight induces changes in synaptic organization of the developing neocortex. Unborn and newly born mammals show the greatest increase in brain plasticity. Without gravitational resistance, the circulatory system is impaired in its ability to pump blood from the lower extremities back to the upper body and brain. Just as one would expect, neonates are particularly sensitive to the effects of microgravity during spaceflight, exhibiting such characteristics as underdevelopment of lower limbs (DeFelipe et al. 2002). These underdeveloped limbs may become vestigial, or degenerate over time, thereby resolving the issue of cardiac insufficiency. Hearts that do not need to pump blood into lower extremities need not expend energy doing so, and instead will devote their energies into more adaptive functions. Generations born into the weightless world will thus reflect their environment in their genetic, anatomical and functional evolution.

Under the effects of hypergravity bones and muscles grow bigger and stronger, and hearts circulate more oxygen than before. Humans who live in hypergravity will adapt into beings whose bones, muscles and cardiac systems are larger and stronger than today's humans.

What this means for humans in space is that first-time settlers trained in hypergravity via centrifuge both on Earth, en-route and in the extraterrestrial space settlement, will benefit by maintaining their own conditioning and that of their offspring until such time as evolution adapts the bodies of their progeny to hypergravity. However, for many who do not intend to return to Earth, but remain in extraterrestrial space settlements, or who remain spacefarers, these issues may be unimportant, and their biological systems will have ample opportunity to restructure and reorganize themselves under either microgravity or hypergravity.

Our work to understand the psychological and physiological alterations to humans in space is ongoing. We will continue to explore and write about the changes that are likely to occur and we very much welcome input. References

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