According to the Smithsonian Institution climate will undoubtedly, as before in history affect human evolution. New research asserts that key human adaptations evolved in response to environmental instability. This concept was developed during research conducted by Dr. Rick Potts of the Smithsonian’s Human Origins Program. Natural selection was not always a matter of ‘survival of the fittest’ but also survival of those most adaptable to changing surroundings.
From the beginning it is apparent that human evolution has coincided with environmental change, including warming, cooling drying, and wider climate fluctuations over time. How did environmental change shape the evolution of new adaptations, the origin and extinction of early archaic hominin species Homo erectus, Neanderthal, Denisovan, and the emergence of the modern African born species, Homo sapiens?
There are many ideas about the role of the environment in human evolution. Some views assume that certain adaptations, such as upright walking or toolmaking, were associated with drier habitat and the spread of grasslands, an idea often known as the savanna hypothesis. According to this long-held view, many important human adaptations arose in the African savanna or were influenced by the environmental pressure of an expanding dry grassland.
One way organisms can cope with environmental fluctuation is through genetic adaptation, where several alleles, or different versions of genes, are present in the population at different frequencies. As conditions change, natural selection favors one allele or genetic variant over another. Genes that can facilitate a range of different forms under different environments (phenotypic plasticity) can also help an organism adapt to changing conditions.
Another response to environmental change is to evolve structures and behaviors that can be used to cope with different environments. The selection of these structures and behaviors as a result of environmental instability is known as variability selection. This hypothesis differs from those based on consistent environmental trends. Environmental change in an overall direction leads to specializations for those specific conditions. But if the environment becomes highly variable, specializations for particular environments would be less advantageous than structures and behaviors that enable coping with changing and unpredictable conditions.
Variability selection refers to the benefits conferred by variations in behavior that help organisms survive change. To test the variability selection hypothesis, and to compare it with habitat-specific hypotheses, Potts examined the hominin fossil record and the records of environmental change during the time of human evolution.
If environmental instability was the key factor favoring human adaptations, new adaptations would be expected to occur during periods of increased environmental variability, and these adaptations would have improved the ability of early human ancestors to deal with habitat change and environmental diversity.
If this is the case the greatest enemy to human survival is lack of genetic diversity! Europeans have been the focus of some of the largest studies of genetic diversity in any species to date. Recent genome-wide data have reinforced the hypothesis that present-day European genetic diversity is strongly correlated with geography which would in part explain the natural declines in population upon the onset of climate change. Simplistic notions of genetic determinism have also fallen aside as most human traits are now thought to be driven by complex interactions between multiple environmental and genetic factors. Culturally, there is a wider appreciation that diversity also makes a positive contribution to the genetic survival of a society.
Lack of genetic diversity can lead to extinction. When genetic diversity gets too low, species can go extinct due to the combined effects of inbreeding depression and failure to adapt to change. Rapid reductions in genetic diversity increase the risk of extinction. The introduction of new alleles can save a population, which is called genetic rescue. By moving individuals between populations and allowing those individuals to interbreed with local populations, we generate offspring with increased genetic diversity. Once fragmented, or reduced in size for other reasons, populations become prone to the loss of genetic diversity through a process called genetic drift.
Hemophilia A (HA) and hemophilia B (HB) are rare bleeding disorders caused by genetic defects in the genes encoding coagulation factor VIII (FVIII) and factor IX (FIX), leading to deficiency or absence of either of the two coagulation proteins. Increasing temperature weakens the positive effect of genetic diversity on population growth less diversity means less children. Recently this genetic diversity was expressed in the Covid pandemic which scientists discovered did little damage to African populations that not only had a genetic structure that kept them safe from the more lethal forms of the disease, but a study of blood samples found 78 percent of West African people have Covid antibodies (although few are vaccinated). The World Health Organization says it’s at least 65 percent across Africa.
In 2022 countries like Malawi entered something akin to what many countries still struggling with massive omicron waves consider the holy grail: the endemic stage of the pandemic, in which the coronavirus becomes a more predictable seasonal bug like the flu or common cold. In fact, top scientists in Africa say Malawi is just one of many countries on the continent that appear to have already reached — if not quite endemicity — at least a substantially less threatening stage. Probably less than 10% [of the population], have tested positive for Covid! A gene called HLA-DQA2, prevalent in Sub Saharan African populations which was expressed (activated to produce a protein) at a much higher level in people who did not go on to develop a sustained or life threatening Covid infection and could hence be used as a marker of protection.
Using single-cell sequencing, researchers from the Wellcome Sanger Institute, University College London (UCL), Imperial College London, the Netherlands Cancer Institute and their collaborators, studied immune responses against SARS-CoV-2 infection in healthy adult volunteers, as part of the world's first COVID-19 human challenge study. Most Black or African exposed participants did not go on to develop a COVID-19 infection, allowing the team to uncover unique immune responses associated with African resistance to sustained viral infection and disease.
Individuals mostly of African descent who immediately cleared the virus did not show a typical widespread immune response but instead mounted subtle, never-seen-before innate immune responses. Researchers suggest high levels of activity of a gene called HLA-DQA2 before exposure also helped people prevent a sustained infection from taking hold. In contrast, the six individuals who developed a sustained SARS-CoV-2 infection exhibited a rapid immune response in the blood but a slower immune response in the nose, allowing the virus to establish itself there. Everyone has HLA-DQ genes. In fact, everyone inherits two copies of HLA-DQ genes—one from their mother and one from their father. There are many different types of HLA-DQ genes,HLA-DQA2 (Major Histocompatibility Complex, Class II, DQ Alpha 2) is a Protein Coding gene.
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