Why Evolution is True is a blog written by Jerry Coyne, centered on evolution and biology but also dealing with diverse topics like politics, culture, and cats.
This video showed up as a “suggestion” when I was watching YouTube (no, I’m not a Nazi), and I was curious to see what the last German propaganda newsreel of WWII showed. Among other things, which are explained in the 12½-minute clip, is the last video taken of Hitler, showing his left hand shaking violently (5:34), a symptom medical historians have attributed to Parkinson’s disease. (This bit wasn’t shown in the final video.) Hitler committed suicide on April 30, 1945—just five weeks after this newsreel appeared in German cinemas.
The footnotes show the direct translation, but there’s English narration of what’s going on in the video beginning 48 seconds in.
Die Deutsche Wochenschau (German for ‘The German Weekly Review’, lit. ‘The German Weekly Look‘ or ‘The German Weekly Show‘) is the title of the unified newsreel series released in the cinemas of Nazi Germany from June 1940 until the end of World War II, with the final edition issued on 22 March 1945. The co-ordinated newsreel production was set up as a vital instrument for the mass distribution of Nazi propaganda at war. Today the preserved Wochenschau short films make up a significant part of the audiovisual records of the Nazi era.
. . . Among the many notable scenes preserved by the newsreel are the Nazi point of view during the Battle of Normandy, the footage of Hitler and Mussolini right after the 20 July plot, and the last footage (No. 755) of Hitler awarding the Iron Cross to Hitler Youth volunteers in the garden of the Reich Chancellery shortly before the Battle of Berlin. Its last documentary, Traitors before the People’s Court, depicted the trial of the accused in the 20 July plot, and was never shown.
It’s fascinating to see how, with the Russians closing in on Berlin, the German people were not told of it but instead were misled to think that they might successfully resist the enemy.
I never would have selected this book on my own, but fortunately a reader suggested it, and I’m very glad. The book, Empire of the Summer Moon: Quanah Parker and the Rise and Fall of the Comanches, the Most Powerful Indian Tribe in American History, by S. C. Gwynne III, is a history of the Native Americans of the Great Plains extending from about 1830 to the beginning of the 20th century. This is the period when all the tribes (the book calls them “Indians”, not “Native Americans”)—and there were many tribes and sub-tribes—came into conflict with Mexicans and with Americans moving West, and we know how that ends.
The history centers on the Comanches, the dominant tribe on the plains, though there was never one hierarchical tribe but a series of sub-tribes that were loosely affiliated as a “nation” and would sometimes join forces or fragment. Gwynne did a great deal of historical research using primary documents, and the result is a informative but mesmerizing tale, one that is hard to put down.
The Comanches were nomads, ranging widely over the Great Plains from Colorado to Texas. Their “villages” were only temporary, and would be moved (by women, who did the heavy lifting) from place to place during wars or buffalo hunts. And those were really their two primary activities: killing members of other tribes and killing buffalo, which were then so numerous then that their herds could extend to the horizon. An important part of Comanche culture was the horse; Comanches were nearly always mounted in war or on the hunt, with horses descended from those brought to the Americas by the Spanish. As you can see from the photo of a Comanche warrior below, the horses were small, descended from wild mustangs caught and “broken” with great skill. Comanches also specialized in stealing horses from other tribes and from settlers and the American military. Horses were their riches.
Comanche horsemanship was superb, largely accounting for their success against other tribes and against settlers. They were able, for instance, to ride sideways on the horse’s flank, not visible to enemies on the other side, and shoot arrows (with tremendous accuracy) from below the horse’s neck. Until they managed to get firearms from the settlers and soldiers, they used arrows and lances, and that is how they brought down buffalo. (The butchering, of course, was done by the women.)
I won’t go into detail about the lives and wars of the Comanche, except to say that the book imparts three lessons about Native Americans on the plains:
First, they did not “own” land or even occupy it. As I said, they were nomadic, and many other Native American tribes, including Apaches, Cherokees, Kickapoos, and Arapaho, roamed the same territory. This bears on the present-day conflict about repatriating artifacts and human remains to tribes that claim them. For artifacts or bones found on the Great Plains (and elsewhere, of course) cannot be ascribed to a given tribe without DNA analysis, which is almost never done, or if there are distinctive signs from the artifacts identifying them as belonging to a given group. Since this is rarely possible, it becomes a crapshoot about what to do about repatriating Native American artifacts, most of which now have to be returned to a tribe that claims them before scientists or anthropologists get to study them. Read the books and writings of Elizabeth Weiss to learn more about this conflict.
Second, war was a way of life for the Comanche; they were always at war with one tribe or another—even well before white settlers moved West. The view that all was peaceful among Native Americans until white settlers invaded “Indian” land and displaced the residents is grossly mistaken. Young men were trained for war beginning at five or six, and the youths were skillful with the horse and the bow. Comanche life without war was unthinkable, and the men prided themselves, and rose in rank in their groups, largely through skill in warfare. In the end, the Comanches were diminished not because of lack of skill in fighting, but because they were outnumbered by settlers and the Army, because the Army had superior weapons, especially cannons, and because the settlers killed off their main means of subsistence: the buffalo. The number of Comanche is estimated to have fallen from about 40,000 in 1832 to only 1,171 in 1910. The book describes many treaties between the Comanche and the U.S. government or its agents, but these treaties were almost always broken by one side or another—or both.
Third, their life was very hard. They subsisted almost entirely on buffalo, had to weather the brutal cold of the Plains in tipis or on horseback, often went without food or water, and of course almost never bathed. (This was tough on the women, who became covered with blood and guts when skinning buffalo.) But they prided themselves on their toughness and bravery. (women often fought alongside the men). These features were mixed with an almost unimaginable degree of cruelty towards their enemies. Enemies who were not killed outright were tortured, and in horrible ways: scalping, cutting, and roasting to death slowly. These acts were considered normal and not immoral, though the white settlers (who were often tortured as captives) saw them as brutal and primitive. But the Comanche were capable of great kindness as well, especially towards other members of their tribe and occasionally towards white women and children who survived battle with the tribes and were “kidnapped’ by them, many becoming, in effect, Comanches themselves.
This brings us to the centerpiece of the story: the abduction of an American woman, Cynthia Ann Parker, in a battle in 1836. She was eight years old. Parker became integrated into the tribe, learned their language (eventually forgetting much of her English) and married a Comanche chief, Peta Nocona. Among their three children was Quanah Parker, who showed tremendous skill, wisdom, and courage as a warrior, and rose through the ranks (despite being half white) to become a chief himself. The story of Quanah is the story of the decline and fall of the Comanches, limned with many battles and culminating in their surrender to American soldiers and sedentary occupation of land on a reservation, where of course they were unhappy. Quanah demonstrated his leadership skills even on the reservation and, through judicious rental of reservation land to settlers for grazing cattle, became wealthy and renowned among both whites and Native Americans. Here’s a photo of Quanah in his native clothing:
Daniel P. Sink of Vernon Texas, Public domain, via Wikimedia Commons
Gwynne skillfully weaves together the story of Quanah and greater historical events, so in the end you understand not just the history of the extirpation of Native Americans, but the life of Comanches and the personalities of Quanah and his mother, Cynthia Parker. Parker herself was captured by the Texas Rangers when she was 33 and lived the rest of her life with settlers, including members of her extended family. She was never happy, and tried to escape back to the Comanches several times, but never succeeded. She had several children, including Quanah, but was separated from her sons and left with only one daughter, Topsannah (“Prairie Flower”). Cynthia died at 40, heartbroken. Here’s a photo of her with Topsannah. Despite arduous efforts of settlers to assimilate Cynthia back as an American, she was always a Comanche at heart. The expression on her face tells the tale.
Here’s Quanah in 1889. As you see, he adopted many of the settlers’ ways, including their clothing, But he never cut his braids:
Charles Milton Bell, Public domain, via Wikimedia Commons
I’ve run on too long, but I give this book an enthusiastic recommendation and thank the reader who recommended it. Although it may strike you as something you might not like, do give it a try. (Click on the picture below to go to the publisher.) You may know about the sad history of the extirpation of Native Americans, but this book tells you, more than anything I’ve read, how at least some of them lived their lives as free men and women.
More video today! This one, of course, was suggested to me by YouTube, since I watch a lot of food videos as well as history videos. And it’s exactly the kind of video that I would have to click on, as it lists the favorite foods of every American President.
Here are the Presidents who, in my view, had the best taste (you’ll have to watch to see their favorites):
Thomas Jefferson
James Madison
James Monroe
John Tyler
James K. Polk
Abraham Lincoln
Ulysses S. Grant
Teddy Roosevelt
William Howard Taft
Woodrow Wilson
Lyndon Johnson***
Jimmy Carter
LBJ gets the kudos for liking the best dish, and, looking over the list, I see that it’s weighted with Presidents who liked Southern food. No surprise, as it’s America’s best regional cuisine. They do mention a McDonald’s Filet O’ Fish as Trump’s favorite, but I thought he liked Big Macs better. Either way, he doesn’t make the list.
If you have some good wildlife photos, please send them in. Thanks!
Today we have a text-and-photo tale by Athayde Tonhasca Júnior on his favorite topic: pollination, but also on sex and gender in plants. You should be impressed at the cleverness of plants in having evolved to facilitate reproduction through pollinators. Athayde’s narrative is indented, and you can enlarge the photos by clicking on them.
Nifty gender bias
Once upon a time in Ancient Greece, a young man was sauntering in the woods, enjoying the fine weather, unaware he was approaching a pond inhabited by the naiad Salmacis. Like all naiads, the minor deities that oversaw springs, wells and lakes, Salmacis had a weak spot for youthful, virile men. Awestruck by the lad’s beauty, Salmacis tried to seduce him. Her lascivious prattle only managed to alarm the visitor, so she pretended to give up and walked away. The young man, possibly flustered by the naiad’s unladylike harassment, decided to go for a dip in the pond. Beautiful he might have been, but not very smart: freshwater bodies were naiads’ territory. From behind a tree, Salmacis saw her chance. She leapt into the water to have another go at the shy looker, and the poet Ovid tells us what happened next: She poured herself all over the young man, and finally coiled herself right round him as he struggled against her and tried to slip out of her grasp. She was like a snake whom an eagle, the king of birds, snatches and holds up on high. (Metamorphoses, Book 4). Salmacis, who today would be on the Sex Offender Register, realised that her less than refined tactics were not working. In desperation, she begged the gods to let the two of them stay together forever. The gods complied, but interpreted the feisty naiad’s wishes literally. They merged Salmacis and her quarry in one body, creating a deity half man and half woman, with male and female parts. Perhaps an ironic destiny for a man whose name was also the product of a blend. A son of Hermes, the messenger of the gods, and Aphrodite, the goddess of love and beauty, the youth was called Hermaphroditus.
To 18th century naturalists, who were well versed in the Classics, Hermaphroditus was an ideal trope for a biological phenomenon known from ancient times: the existence of plants and animals with male and female reproductive organs. As biology progressed, the term ‘hermaphrodite’ began to be applied to sexually reproducing organisms that produce male and female gametes. Roughly 5% of all animals, mostly invertebrates, fulfill the condition. Among vertebrates, hermaphrodism is found only in some fishes and frogs: the great majority of species are gonochoric, that is, either male or female; the rare instances of hermaphroditism are considered pathologies.
Hermaphroditism may be unusual among animals, but it’s the way of life for most flowering plants. About 90% of them are functionally hermaphrodites, either by having male and female reproductive parts in the same flower or having male and female flowers in the same plant (these are known as monoecious). Hermaphroditism opens the door for self-fertilization, a handy strategy when mates or pollinators are rare or absent. But this type of shortcut in the dating game has severe disadvantages: it reduces genetic diversity, leading to lower capacity to survive and reproduce, and to adapt to changing environments. So it is not surprising that many hermaphroditic plants have developed physical and genetic barriers to avoid or reduce the possibility of self-fertilisation. Some species inhibit the germination of their own pollen grains; for others, their sex bits are morphologically different, such as long stamens and short styles or vice-versa (herkogamy); some resort to temporal separation of male and female stages (dichogamy).
If self-fertilisation was to be the norm among hermaphroditic plants, Charles Darwin’s evolutionary theory would be seriously dented because outcrossing (the interbreeding of unrelated individuals) sets the stage for adaptation by natural selection. Understandably, Darwin paid much attention to pollination mechanisms in his book about orchids (Darwin, 1862) that followed On the Origin of Species by Means of Natural Selection. His research and observations paid off: he closed his orchid book by stating it is hardly an exaggeration to say that Nature tells us, in the most emphatic manner, that she abhors perpetual self-fertilisation.
While investigating the ways orchids avoid self-fertilisation, Darwin discovered a particularly clever instance involving the autumn lady’s-tresses orchid (Spiranthes spiralis, then known as S. autumnalis), and bumble bees (Bombus spp.), its main pollinators. This orchid produces an erect, unbranched flowering stalk, 7-20 cm tall. Flowers bloom from the bottom of the stalk to the top and are protandrous, a form of dichogamy where male reproductive organs mature before the female ones (studying botany is a sure way to improve your Scrabble scores). These traits are important for what Darwin observed in relation to the behaviour of visiting ‘humble bees’. In his own words: The bees always alighted at the bottom of the spike, and, crawling spirally up it, sucked one flower after the other. I believe humble-bees generally act thus when visiting a dense spike of flowers, as it is most convenient for them; in the same manner as a woodpecker always climbs up a tree in search of insects. This seems a most insignificant observation; but see the result. The result is thus: a bee alighting on the lowest flowers and making her way up may pick up some pollinia (sticky blobs of pollen grains typical of orchids) that may get transferred to apical flowers. However, this pollen will be wasted because upper flowers are functionally male; their pollen is ready to be taken away but their female parts are not yet mature. Bees that gather pollen from apical flowers fly away to the bottom of another stalk, where flowers are older and therefore receptive (functionally female). Thus, cross-fertilisation is assured. This setting has been labelled Darwin’s inflorescence configuration, a fitting tribute to his skills in observation, experimentation and deduction.
Like the autumn lady’s-tresses, the rosebay willowherb (Chamaenerion angustifolium) is hermaphroditic, protandrous, has an inflorescence that blooms from bottom to top, and is pollinated by bees, mostly Western honey bees (Apis mellifera) and bumble bees. Rosebay willowherb too takes advantage of bees’ stereotypical foraging behaviour of moving up along erect inflorescences, but it goes one step further to encourage visitors to follow the script: flowers at the bottom of the inflorescence produce about 1.4 times more nectar than apical flowers (Antoń et al., 2017). Many bees and other pollinators visit flowers sequentially from the highest to the lowest quality, and stop inspecting those below a threshold (Carlson & Harms, 2006). This foraging strategy works to a T for the rosebay willowherb: a bee starts at the bottom where nectar is best, makes her way to less rewarding but pollen-bearing apical flowers, then flies away, hopefully taking some pollinia along.
Functionally female or male flowers secreting more nectar than their counterparts is known as gender-biased nectar production. This phenomenon is relatively uncommon (although data are limited) but has been reported for a range of unrelated species, which suggests it evolved independently several times. Most known examples consist of biases towards functionally female flowers, just like the rosebay willowherb, and in most cases Darwin’s inflorescence configuration and bee pollination are involved (Strelin et al., 2025). We don’t know for sure whether gender-biased nectar production increases the probability of pollen transfer and promotes outcrossing, but it’s a reasonable assumption.
Charles Darwin considered himself a mediocre botanist, even though eight of the ten books he published after On the Origin were about various aspects of plant biology, particularly reproduction (Barrett, 2010). The great naturalist was fascinated by flowers’ ‘beautiful contrivances’ that assured outcrossing and avoided the traps of inbreeding. When we look at the pas de deux performed by the autumn lady’s-tresses and rosebay willowherb with their pollinating bees to keep their hermaphrodite flowers on the straight and narrow towards cross-fertilisation, we can’t help but share Darwin’s fascination.
Today we have a text-and-photo essay by reader Athayde Tonhasca Júnior. His captions and descriptions are indented, and you can enlarge his photos by clicking on them.
Bubbling sans blubbing
We don’t know much about Marcus Terentius Varro (116–27 BC), but it’s safe to assume this Roman polymath was no slacker. Varro wrote about history, theology, philosophy, language, literature, rhetoric, music, medicine, geography, architecture, law and agriculture, including apiculture (the Varroa genus of parasitic mites that plague honey bees was named after him). Near the end of his life, Varro wrote res rusticae (Country Matters), the last of his reported 490 publications. Possibly gripped by a sense of irrevocability about what was soon to come, Varro opens res rusticae with a sentence that says …ut dicitur, si est homo bulla, eo magis senex (…as they say, man is a bubble, all the more so is an old man). Varro’s image of life as ephemeral and fragile as a bubble was picked up by the Dutch humanist and philosopher Erasmus (1466-1536), who popularised the saying homo bulla est (man is a bubble). Erasmus in turn hit a chord with baroque Dutch painters who had started the vanitas (futility) movement, a style focussed on depicting the transience of life, the pointlessness of earthly pursuits, the inevitability of death. Vanitas painters were partial to dark environs, extinguished candles, flowers, clocks, hourglasses, skeletons, skulls, and lots of bubbles.
Hendrick Goltzius (Netherlandish, Mühlbracht 1558–1617 Haarlem) Quis evadet?, 1594 Netherlandish, Engraving; sheet: 8 1/4 x 6 in. (21 x 15.2 cm) The Metropolitan Museum of Art, New York, The Elisha Whittelsey Collection, The Elisha Whittelsey Fund, 1951 (51.501.4929)
The appeal of this less than cheery theme wasn’t to last: not many art patrons wanted to be reminded of their approaching death every time they looked at a painting on the wall. The Dutch artists needed another source of inspiration. They kept the bubbles, but now depicted as aids to children playing games and having fun – bubbles of a joyful variety instead of portents of oblivion (Kareem, 2005).
To this day, blowing soap bubbles thrills and entertains many a child. But to several bee species, blowing bubbles is no laughing matter.
The great majority of the more than 20,000 known bee species depend on nectar from flowers as their main source of energy. Nectar, secreted by specialised glands (nectaries), contains sugars, mostly glucose, fructose and sucrose. Free amino acids, proteins, minerals and lipids add to the mixture’s nutritional content, although we have only a vague understanding of their workings. Besides bees, wasps, hover flies, mosquitoes, butterflies, moths, hummingbirds and bats are among the most enthusiastic consumers of this ready-to-use source of carbohydrates and nitrogen.
The sugar content of flowers from different plants varies considerably, and one could expect bees preferring the sugar-rich ones. But they face a mechanical obstacle: the sweetest nectars offer the greatest energetic rewards, but are hard to extract because of their viscosity. And the longer bees work on the sticky stuff, the more they are exposed to predators. Based on the balance sheet of energetic rewards and costs, sugar concentrations in the 35-65% range seem to be optimal. That suits plants fine, because 40% is the median value of sugar concentration for bee-visited flowers in many habitats and geographic regions (Pamminger et al., 2019).
Nectars with 35 to 65% sugars may be ideal for harvesting, but not so for preventing spoilage and fermentation during long-term storage. Some bees sort out the problem by removing excess water, thus concentrating the nectar. This process is best understood for the European honey bee (Apis mellifera). A worker returning to the hive passes the nectar to one of her sisters by trophallaxis, which is the transfer of food from one individual to another.
The receiving bee regurgitates a bubble of nectar between her mandibles, then swallows it again. The nectar bubble is exposed to the warm air inside the hive and loses some water to evaporation. The bee repeats the process several times, making the nectar more and more concentrated. But the work is not done. The nectar is transferred to the honeycomb, which the bees fan with their wings to further reduce it. When water content is lowered to about 18%, the nectar has turned into a supersaturated sugar solution – or honey to us. Watch a clear and accurate 6’32” summary of honey bees’ amazing comings and goings to produce honey.
Incidentally, the bubbling activity has led some people to assert that honey is bee vomit. Is it? Vomiting is to eject the stomach contents through the mouth, usually as a reflex to some physiological anomaly. Bubbling and other forms of animal regurgitation are regular occurrences with some purpose other than self-protection. Moreover, nectar collected to become honey is not digested or mixed with food. Rather, it is temporarily stored in the bee’s crop (or honey stomach), a pouch located before the stomach proper. So, despite what you read in the social media, honey is not bee puke.
Solitary bees, i.e., those that don’t live in colonies, don’t have large stashes of honey to care for, but several species also blow bubbles to concentrate the nectar. We don’t know for sure why they do it, but by repeated regurgitation and re-ingestion, bees make their nectar more viscous and possibly better suited for storage – just like for honey bees – but also to be transported, mixed with pollen to be fed to their larvae, or used in nest construction (Portman et al., 2023). Watch the superbly named pure gold-green sweat bee (Augochlora pura) pausing her busy life to work on a bubble.
Some flies, which make up another group of bubbling experts, hint at another function of the practice for bees: thermoregulation. The harshly named – despite being an excellent pollinator – oriental latrine fly (Chrysomya megacephala) lowers its body temperature by pushing a gobbet of liquid food in and out of its mouth several times before swallowing it. As the bubble comes out, evaporation lowers its temperature; when sucked in, it cools the fly’s body (Gomes et al., 2018). This form of evaporative cooling is analogous to what panting dogs and ear-flapping elephants do to keep cool.
We don’t know the extent of bubbling among bees, flies and other practitioners such as hawk moths, sawflies and mosquitoes. Whatever its frequency, bubbling is another clever trick that helps insects succeed out there in the wide harsh world.
While staying at my sister and brother-in-law’s house near Dulles Airport, I encountered a few things of interest. The first is an arrival lunch at Willard’s BBQ near Dulles, and it was crowded, understandable in view of how good the BBQ was, especially for this area. Here’s my lunch of “burnt beef ends” (hard to find, a mixture of crunchy and juicy parts from brisket), along with two “vegetables” (mac and cheese and a fantastic potato salad), BBQ sauce (not needed) cornbread and, of course, sweet iced tea. I’d recommend this place if you are in the area.
And I had a look at the Virginia History textbook that my brother-in-law had when he was about 13. He remembered it as having grossly distorted the horrors of slavery, which it did in a big way.
My sister found a copy of the book online, and I was appalled to see how slavery was described: as a great benefit to slaves, who got vocational education and had kindly masters and good working conditions. It was disgusting. Have a look at how, as kids, we were taught about slavery in Virginia.
The book:
An arriving enslaved person with his family, all decked out in fancy clothes and greeting his new “master” with glee. The family, too, is all happy and spiffy. The reality, of course, was far different, with slave families packed into the holds of the ships, with those who survived sold off soon after being kidnapped from Africa to the U.S., and families often being separated.
This new paper in Nature gives a rare picture of human sacrifice among ancient Mayans from the Yucatán peninsula in Mexico. Paleoanthropologists had found remains before, mostly children, preserved by being tossed in sacred cenotes (wells), but this group of 64 ancient individuals was not only collected, but their DNA was analyzed from the ear bones, giving surprising results about genetic relatedness.
As with the Aztecs, human sacrifice was a fixture of ancient Mayan society, though the people killed (in this case, children) were probably captives rather than residents of the place where the killers lived. Sacrifice could have occurred via either decapitation, extraction of the heart from living individuals, or killing with arrows.
Click below to read the piece, or find the pdf here.
The figure below shows where the remains were found: in a chultún (an underground cistern) next to an airport runway near the ancient Mayan city of Chichén Itzá (now a World Heritage Site), which flourished between about 600 and 1200 A.D. This map gives the location:
(From the paper) a, Location of the Maya region in the Americas. b, Geographical locations of Chichén Itzá and Tixcacaltuyub in the Yucatan Peninsula. c, Stratigraphy for the chultún and the adjacent cave in which the burial was found (adapted from ref. 4). d, Location of the chultún within the archaeological site of Chichén Itzá and its relation to El Castillo (adapted from ref. 10). Modern roads are marked in light grey; the chultún abuts an airport runway.
They found the bones of 64 individuals, carbon-dated as being from the 7th to the 12 centuries AD. How did they know how many individuals were represented in their sample? Because they recovered 64 left petrous parts, the bit of the skull’s temporal bone that surrounds the inner ear (this bone, sequestered away from the outside of the skull, is often used to extract ancient DNA). 64 left petrous bones means 64 individuals.
First, every one of the individuals was a male between 3 and 6 years old, showing that the Mayans preferred to sacrifice young boys. Why? It’s not clear, but there’s speculation that sacrifices helped local maize crops flourish (the method of sacrifice wasn’t specified in the paper). However, other sacrificed individuals recovered, as in the famous sacred cenote, have been mixtures of males and females, but also overrepresented with children. The authors don’t speculate why, in this location, only boys were killed.
The ancestry of the sacrificed individuals was compared among each other, as well as to 68 individuals of Mayan descent living the nearby town of Tixcacaltuyub. One surprising finding was that those sacrificed included two pairs of identical (monozygotic) twins (easily seen in DNA, which is identical among two different earbones). The authors note that twins held a special position in Mayan mythology. But, as the plot of “pairwise mismatch rates” shows below), 11 pair of individuals were “close relatives”, represented by the hollow diamonds (the twins, with a mismatch rate of zero, are the two pairs of twins. The authors speculate (see below) that the individuals came from a single big event of mass killing.
The paper doesn’t say how “close” the “close relatives were”, or whether they were contemporaneous, like brothers, but given the age of the individuals, it seems likely that the related pair members came from the same family.
(From paper): e, Genetic pairwise mismatch rate (PMR) for child pairs in the chultún identifies 11 close relative pairs (hollow diamonds), including two pairs of monozygotic twins (highlighted in grey). A low overall PMR for unrelated individuals (black triangles) confirms low genetic diversity in the population; only pairs with PMR < 0.20 are visualized in the plot. See Supplementary Fig. 2 for individual annotations.
The comparison of the DNA of the sacrificed children with that of living people in Tixcacaltuyub, as in the principal-component cluster graph below, showed that the sacrificed individuals )”YCH”, dark purple stars) fell into a cluster of Native Americans, other Mayan individuals, people from Belize, and individuals from the nearby town (“TIX”, light blue stars), and were considerably different from individuals in Africa, Asia, and Oceania, as expected. (This shows diagnostic genetic differences between geographic groups, demonstrating that the idea of “races”—defined as “diagnostically genetically differentiated populations”—is not purely a social construct, but contains biological information.) However, the ancient sacrificed individuals, which also had a dollop of genes from the Caribbean, didn’t particularly cluster with the present day Mayans living nearby, who had their own admixture of genes from Africa and Europe, perhaps reflecting turnover of populations over time. In the sixteenth century there was a big poulation bottleneck, perhaps due to diseases introduced by Europeans. In fact, this bottleneck reduced the population of what is now Mexico by 90%!)
(From paper): (From paper): a, PCA showing ancient Chichén Itzá (YCH) individuals and present-day Tixcacaltuyub (TIX) in a worldwide PCA plot.
One other bit of information. We are able, looking at contemporary DNA sequences of a population, to judge whether natural selection is acting on genes or groups of genes. If variable genes such as the HLA (“human leukocyte antigen”) genes involved in immune response show coordinated variation (that is, variant “A” of one gene tends to co-occur with variant “B” of another gene in individuals), this gives evidence that selection is acting on groups of genes—in this case genes affecting immunity. The authors identified several HLA variants that look like they were subject to selection, and also tested some by making copies of sequences of some HLA variants and seeing how strongly they bound to proteins derived from Salmonella bacteria (strong binding means that the HLA proteins were reacting and presumably neutralizing the bacterial proteins). The authors suggest that the selection acting to promote the rise in frequency of some HLA variants was due to typhoid or paratyphoid-like infections.
The upshot: Although the data from HLA genes does indicate that there was selection for immunity in both ancient and historic times, what I find most interesting is that the sacrifice involved children, all male children, and many were close relatives. This, at least, gives us a pretty strong sociological picture of one aspect of ancient Mayan culture. To quote the authors,
In comparing the subadults in the chultún to other ancient and present-day populations in the Maya region, we find evidence of long-term genetic continuity, which also suggests that the sacrificed children and sibling pairs at Chichén Itzá were obtained from nearby ancient Maya communities. Among present-day individuals at TIX, we detect evidence of European and African admixture since the Contact period.
and
Overall, 25% of the children had a close relative within the assemblage, suggesting that the sacrificed children may have been specifically selected for their close biological kinship. Moreover, this may underestimate the true number of relatives present in chultún as only 64 of the estimated 106 individuals in the chultún had a preserved petrous portion of the left temporal bone available for analysis. The further finding that the closely related children in each set seem to have consumed a similar diet and died at a similar age suggests that they have been sacrificed during the same ritual event as a pair or twin sacrifice.
and, finally,
The discovery of two sets of identical twins, as well as other close relatives, in a ritual mass burial of male children suggests that young boys may have been selected for sacrifice because of their biological kinship and the importance of twins in Maya mythology. We show that, at a genome-wide level, the present-day Maya of Tixcacaltuyub exhibit genetic continuity with the ancient Maya who once inhabited Chichén Itzá and we demonstrate through several lines of evidence the involvement of the HLA region in a pathogen-driven selection event(s) probably caused by infectious diseases brought into the Americas by Europeans during the colonial period.
The interest of the Mayans in identical twins reminds me of Josef Mengele in Auschwitz, who also took a particular interest in twins, but in his case he did gruesome experiments on them before killing them.
