Jay Storz at the University of Nebraska was hiking with colleagues on one of the most godforsaken habitats on the planet: windswept, low-oxygen volcanic peaks in Argentina. It was like exploring Mars. That was until they found carcasses of mummified mice beside a rock pile. How did they get there? It’s freezing. There’s no food. There’s no water. Everywhere one looks there is only bare rock. Phys.org quotes Dr. Storz:
“Well-trained mountain climbers can tolerate such extreme elevations during a one-day summit attempt, but the fact that mice are actually living at such elevations demonstrates that we have underestimated the physiological tolerances of small mammals.” [Emphasis added.]
Once they knew what to look for, they found over a dozen other mice remains on 18 summits above 6,000 meters (19,500 feet). Radiocarbon dating showed they had died within the last few hundred years.
The evidence indicated that the mice were not one-day visitors scampering up for the view but were members of populations thriving at that elevation.
“The discovery of the mouse mummies on the summits of these freezing, wind-scoured volcano summits was a huge surprise,” Storz says. “In combination with our live-capture records of mice on the summits and flanks of other high elevation Andean volcanoes, we are amassing more and more evidence that there are long-term resident populations of mice living at extreme elevations.”
A Personal Experience
It reminded me of a personal experience (pictured above) at a lower elevation that was near my limit: the 14,500-foot summit of California’s Mount Whitney, highest peak in the contiguous 48 states. I can only imagine the difficulty hiking up another 5,000 feet in the Andes. Gasping for air every 20 steps or so as I forced myself to the top of my unimpressive peak-bagging record, I was greeted by eager marmots and birds looking for handouts like they were on a picnic.
The finding now raises important questions, including how mammals can live in a barren world of rock, ice, and snow where the temperatures are never above freezing, and there is roughly half the oxygen available at sea level. It’s not clear why the mice would have climbed to such heights.
The paper by Storz and colleagues in Current Biology doesn’t mention evolution or natural selection. Genetic tests on the mice, identified as members of Phyllotis vaccarum, did not indicate any noteworthy differences from the populations that live at lower elevations.
Average genome-wide pairwise nucleotide diversity for the total sample of mice was typical for natural populations of rodents (π = 0.42%). After filtering our dataset to 42 mice, excluding two closely related individuals, we confirmed that the summit mice exhibited close affinities to the Phyllotis vaccarum reference genome and other live-trapped specimens of P. vaccarum from lower elevations on the flanks of the same volcanoes and in the surrounding Altiplano (Figure 1B,C). Results of a model-based clustering analysis revealed very low population structure in the total sample, as proportional assignments of ancestry to genetically defined clusters were similar for mice from all localities (Figure 1B). A principal component analysis of genomic variation also revealed low levels of population structure across the surveyed region, as PC1 and PC2 explained only 6.94% and 2.36% of total variation, respectively, and the patterning of variation did not distinguish the set of summit mice from mice collected at less extreme elevations in the surrounding region (Figure 1C).
Conclusion: scientists had underestimated the adaptability of small mammals to extreme elevations. “Such extreme elevations were previously assumed to be completely uninhabitable by mammals,” they said. The results “challenge assumptions about the environmental limits of vertebrate life and the physiological tolerances of small mammals.”
A large team of 22 mostly Italian researchers, publishing by the bioRxiv preprint server, discusses their opinions on how “Convergent evolution of complex adaptive traits enabled human life at high altitudes.” As a side anecdote, one of the authors, a member of the Mount Everest Summiters Club in Nepal, has the listed surname “Sherpa” — the word indicating those noble but underappreciated guides who help flatlanders carry their packs up the highest mountains on Earth. They trot around on those trails like it’s a walk in the park.
This team does invoke evolutionary theory. They looked for genetic clues of adaptation by natural selection for people groups who live at high elevations.
Convergent adaptations represent paradigmatic examples of the capacity of natural selection to influence organisms’ biology. However, the possibility to investigate genetic determinants underpinning convergent complex adaptive traits has been offered only recently by methods for inferring polygenic adaptations from genomic data. Relying on this approach, we demonstrate how high-altitude Andean human groups experienced pervasive selective events at angiogenic pathways, which resemble those previously attested for Himalayan populations despite partial convergence at the single-gene level was observed. This provides unprecedented evidence for the drivers of convergent evolution of enhanced blood perfusion in populations exposed to hypobaric hypoxia for thousands of years.
Note to the Authors
The people groups in the study are all members of Homo sapiens. They are fully human, interfertile members of humankind.
In conclusion, the obtained results highlighted polygenic mechanisms mediated by adaptive evolution of several focal adhesion genes as the possible drivers of enhanced angiogenesis and oxygen transport in Andean human groups similarly to what previously observed in Tibetan/Sherpa populations, thus providing unprecedented evidence for the molecular bases of their convergent adaptation to hypobaric hypoxia.
While it may be interesting to compare genomes between mountaineers and flatlanders, nothing in the data requires a Darwinian interpretation. They could only say that certain genes were “possible drivers” of angiogenesis and oxygen transport in the mountaineers. Note the level of speculation in their previous paragraph:
Interestingly, LAMA1/2/3, COL1A2/2A1/4A2, and ITGA2/4/8/11 have been previously found to participate to gene networks targeted by natural selection in Tibetan and Sherpa populations. Such an incomplete genetic convergence between Andean and Himalayan high-altitude peoples is not unexpected within the framework of an evolutionary scenario largely characterized by polygenic adaptive events, in which single loci play a negligible role with respect to their overall synergic interactions. Nevertheless, we provided evidence for the same biological functions/pathways (i.e., those related to angiogenetic processes) having adaptively evolved in both the considered populations, plausibly in response to the selective pressure imposed by hypobaric hypoxia. The identified genetic signatures might indeed contribute to the increase in the density of blood vessels that results in an improved blood flow and oxygen delivery to tissues despite the hypoxic stress, which is an adaptive trait qualitatively (but not quantitatively) similar between Andean and Himalayan groups (Gnecchi-Ruscone et al., 2018; Sharma et al., 2022; Wu et al., 2022). In fact, such a trait appears to be more enhanced and generalized in Tibetan/Sherpa populations with respect to Andean ones, being especially limited to improved uterine artery blood flow during pregnancy in the latter groups (Beall, 2007; Julian & Moore, 2019). The fact that several of the adaptive loci identified in the present study (e.g., PTK2, VEGFA, PDGFA, and PDGFD) play a pivotal role in the development of vascular tissue specifically in placenta and embryo, and thus in the establishment of efficient maternal-fetal circulation (Shen et al., 2005; Adams & Alitalo, 2007; Khankin & Karumanchi, 2010; Russell et al., 2019), seems to support such an observation. Moreover, it might suggest that natural selection succeeded in optimizing angiogenesis in Andean individuals mainly in early life and/or at the reproductive stage, thus leading to improved fetal development during intrauterine life (e.g., in terms of maturation of the respiratory system), which represents a key aspect to reduce neonatal mortality at high altitudes where efficiency of respiratory functions is crucial to ensure the individual’s survival.
“Might” Does Not Make Right
How many babies had to die in the womb before the essential genes to survive hypobaric hypoxia mutated in lucky zygotes to allow them to tolerate the thin air? How many mothers and fathers needed the same mutations? How many adults perished waiting for the beneficial mutations to become fixed in the population? (This is called “the cost of selection” in the literature.)
To follow their example of “possibilities” and “suggestions” in scientific explanation, let’s suggest the possibility that early mountain climbers used their human reason to evaluate all the funerals in the high-altitude camp, concluding, “You know, this was a bad idea. Let’s go back to the coast.”
The engineering model of adaptation being developed by the design community looks at the observable genetic variations differently. Rather than depending on lucky cosmic rays to turn genes into super angiogenesis machines and oxygen transport systems, they identify built-in mechanisms that receive signals from the environment and switch on internal controls that respond to the conditions. Heritable adaptations by epigenetic processes could occur quickly, because they are driven not by random mutations but by foresight and intention in their engineered design.
Moreover, design advocates are not surprised by seeing organisms that are over-engineered for survival, like the mountain mice and the Nepal sherpas. Darwinism has a problem with over-engineered things since it cannot see past the immediate present. We can make this prediction for design theory: fewer human mummies in the Himalayas with desperate expressions on their faces, waiting for the lucky mutations to arrive.