The first change affected blood. While the pH of human blood at the time was usually maintained at roughly 7.4, many people began to show a long-term blood pH of higher than 7.6. These people, remarkably, did not suffer the symptoms commonly associated with alkalemia: muscle pain and spasms. Instead, these individuals enjoyed a normal life, although some data indicate that osteoporosis was more common in affected individuals in the first 100 years the condition was observed. This may have been merely a correlation rather than a result of the changes to blood pH. Importantly, blood from affected individuals was not compatible for transfusion to unaffected individuals, and vice versa. Indeed, if individuals with high-pH blood received transfusion from those without the condition, they often suffered acidemia, including muscle weakness and seizures. Research eventually revealed that individuals with high blood pH carried a novel mutation in the gene for V-ATPase, causing changes to the enzyme that led to an increase of carbonate ions in the blood. These people benefited from high levels of atmospheric carbon dioxide.
Shortly after this change appeared, a change in the composition of adipose tissue in many people emerged. Epigenetic changes were responsible for this shift, which saw a transformation of white adipose tissue to brown adipose tissue, along with a substantial increase in the amount of adipose tissue persisting throughout development and into adulthood, which was associated with a slow metabolism and low body temperature (average 34 degrees Celsius, or 93.2 degrees Fahrenheit). Although these people were first viewed as merely obese, as global temperatures entered what has become known as the Great Heat, these individuals were afforded many levels of protection. In the hot temperatures that became pervasive in the tropics and subtropics, the lower body temperature of those with high levels of brown fat meant that they suffered rarely, if at all, from heat exhaustion or heat stroke. They were additionally able to metabolize the fat in their tissues to generate water, allowing them to survive for as much as thirty days without access to water of any kind. In extreme cold, such as that associated with the localized harsh winters that became common after the Great Heat, these individuals entered a state of hibernation, not unlike that once seen in the now-extinct brown bear.
The final change (and at this point no one was still calling these changes disease) was neural, in both the supramarginal gyri and lateral frontal pole. Prior to this change, only the right supramarginal gyrus was associated with empathy. Today, both the right and the left gyri control this vital social response. Additionally, the lateral frontal pole grew substantially, giving modern humans their characteristic foreheads and allowing for the increase in long-term planning necessary for environmental disaster aversion and restoration. At the same time, the nucleus accumbens underwent a small degree of restructuring, although debate remains as to whether this change had any effect on reward-seeking and long-term planning behaviour. More research into this field is needed.
These changes, which occurred over a mere four generations, had significant biological and social consequences.
Phylogenists disagree regarding exactly when modern humans (Homo consiliens) split from our more primitive ancestors (Homo sapiens), but it is generally agreed to have happened sometime between 200 and 300 years ago. For a few generations, hybrids of Homo consiliens and Homo sapiens were common, and it was difficult to tell the difference between protohumans, Homo sapiens, and modern humans, Homo consiliens. Surprisingly, many protohumans were hostile toward humans and hybrids, possibly a result of their undeveloped left supramarginal gyrus. This led to a decrease in interbreeding, resulting in a genetic segregation of the two Homo populations. As the humans flourished, the ability to produce viable offspring with protohumans was lost.
Socially, the protohumans became more and more tribal, seeking to isolate themselves as much as possible. At first, this was allowed to proceed naturally, as these hominids became extremely hostile and often violent if humans approached them. Over time, however, it became clear that their numbers were dwindling, and the International Council agreed that intervention was necessary. The protohumans were moved to environments most suited to their biology and given as many resources as possible. They were encouraged to breed, and the hardiest offspring were moved among preserves in an effort to increase overall genetic vigour. However, the lack of effective physiological structures for surviving the high-carbon-dioxide atmosphere and temperature fluctuations eventually proved fatal to the species. The last surviving member died merely eighty-six years ago.
Today, a great deal of study is devoted to this species. After all, their history is our history, and they kept abundant written records dating back millennia. There is even some debate about naming them protohumans, as some scholars prefer simply “human.” Their loss is a tragic event, one of uncountable millions of species that perished as a result of the Great Heat.
Copyright © 2019 Elizabeth Rubio.
Image credit: Katrina Archer from DepositPhotos stock images
Elizabeth Rubio lives in Austin, Texas, where she writes science fiction and fantasy, as well as nonfiction. Once a professional biochemist, she believes very strongly that every person is a scientist. She hopes the optimistic scientists of all kinds can work together to create a future for us all. When not writing, she can be found snuggling her cats or at the library. Find her other stories in Analog or Mythic, or look for her nonfiction series from Enslow Publishing.