Natural selection in actrion - High altitude adaption in Tibet

https://www.sciencealert.com/humans-are-evolving-before-our-eyes-on-the-tibetan-plateau
...
We know that there are some environments that
can make us unwell. Mountain climbers often
succumb to altitude sickness – the body's
reaction to a significant drop in atmospheric
pressure, which means less oxygen is taken in
with each breath.
And yet, in high altitudes on the Tibetan
Plateau, where oxygen levels in the air people
breathe are notably lower than lower altitudes,
human communities thrive.
In the more than 10,000 years the region has
been settled, the bodies of those living there
have changed in ways that allow the inhabitants
to make the most of an atmosphere that for most
humans would result in not enough oxygen being
delivered via blood cells to the body's tissues,
a condition known as hypoxia.
...
Beall has been studying the human response to
hypoxic living conditions for years. In research
published in October 2024, she and her team
unveiled some of the specific adaptations in
Tibetan communities: traits that help the blood
deliver oxygen.
To unlock this discovery, the researchers delved
into one of the markers of what we call
evolutionary fitness: reproductive success. Women
who deliver live babies are those who pass on
their traits to the next generation.
The traits that maximize an individual's success
in a given environment are most likely to be
found in women who are able to survive the
stresses of pregnancy and childbirth.
These women are more likely to give birth to more
babies; and those babies, having inherited
survivability traits from their mothers, are also
more likely to survive to adulthood, and pass the
traits on to the next generation.
...
Beall and her team made a study of 417 women
between the ages of 46 and 86 years who have lived
all their lives in Nepal above altitudes of around
3,500 meters (11,480 feet). The researchers
recorded the number of live births, ranging between
0 and 14 per woman for an average of 5.2, as well
as health and physical information and measurements.
Among the things they measured were levels of
hemoglobin, the protein in red blood cells
responsible for delivering oxygen to tissues. They
also measured how much oxygen was being carried by
the hemoglobin. Interestingly, the women who
demonstrated the highest rate of live births had
hemoglobin levels that were neither high nor low,
but average for the testing group.
But the oxygen saturation of the hemoglobin was
high. Together, the results suggest that the
adaptations are able to maximize oxygen delivery
to cells and tissues without thickening the
blood – a result that would place more stress on
the heart as it struggles to pump a higher
viscosity fluid more resistant to flow.
...
https://www.pnas.org/doi/full/10.1073/pnas.2403309121
Higher oxygen content and transport characterize
high-altitude ethnic Tibetan women with the highest
lifetime reproductive success
October 21, 2024