Sunday, June 25, 2023

The Biggest City in the World You Never Heard About: Cahokia

It is the biggest city that you never heard about. It may well have been the biggest city in the world somewhere between 1000 and 1250. With more than ten thousand inhabitants, this city was at least as large as London at the same time. Why, then, have you never heard about it?

The city today is called Cahokia, in southern Illinois. All that remains of it are large earthen mounds built by Native Americans, one basket of soil at a time, in which bones and artifacts were buried. Warrior-priests lived in wooden structures on the flat mound tops. For square miles around the main mound (now called Monks Mound), workers (slaves?) lived in huts and grew vast fields of maize (corn, unknown at the time outside America) and other crops. Except for the lack of brick and stone and cathedrals, it might have looked like a medieval English landscape. The main urban complex covered 1.8 square kilometers but associated areas covered many more square kilometers. All around Monks Mound, even several miles toward the west, there are other mounds, many of them large, though Monks Mound is the largest.


I visited Cahokia in June, 2023, and have posted a video about it [ ].

We do not know who these people were. They left no writing for us to even try to decipher. We do not know what language they spoke or what they called their city or themselves. Based on artistic similarities in pottery, archaeologists have concluded that the Wichita and Caddo tribes are the physical descendants of the mound builders, although these modern tribes have no tradition or memory of a vast civilization.

Cahokia was the center of a small empire. About five other empires were centered around similar mound-cities in North America, each a separate empire (we think). I will write about one other mound city, Spiro, in a later blog essay.

The Cahokia empire was connected to the other empires by a vast trade network that covered most of the eastern deciduous forest. The trails were of dirt well pressed by thousands of feet. Trade goods were carried by hand, as there were no horses, oxen, or wheels. There was also extensive trade by boat. Cahokia was within sight of the Mississippi River, which is why the culture is called the Mississippian Culture. Eight hundred years ago, the urban center was on the east bank, which today is an economically depressed area and includes East St. Louis. Today, St. Louis on the west bank fills the economic role that Cahokia had eight hundred years ago. Then as now, the Mississippi carried commercial shipping. Today, freeways (of which St. Louis has numerous large ones) have replaced trails.

Trade goods were usually high-value decorative items. As far as we know, food was not usually transported, since the amount needed would weigh too much. Most of the food was corn, beans, and squash, with venison and “wild” nuts for protein. Remains of copper, shell, and sandstone artifacts have been found, and it is possible that perishable items such as clothes and blankets may have been imported. The shells came from the Gulf of Mexico. The copper came from the Great Lakes area, and some of it was reshaped into new artifacts in a copper workshop at Cahokia. Pipe bowls were made from a soft light brown clay similar to that found today in the vicinity of Pipestone, Minnesota. Though the Mississippian culture did not extend into Mexico, there was some trade with the Natives we collectively call “the Aztecs.”

Nobody knows why the Mississippian civilization collapsed. There was apparently a major drought about 1300, but this might not have by itself caused food production to collapse. There was undoubtedly soil erosion caused by the intensive agriculture needed to feed the population, although this would also probably have not caused the collapse. Most likely, it was these two factors (and others?) working together.

You cannot see the Mississippi River today from even the top of Monks Mound, accessible by a modern stairway. The view of the river is not blocked by modern buildings. It is blocked by trees such as oak and elm which have grown back since European and white American occupation. Native Americans cut down small trees and used fire to clear away saplings and undergrowth. The Natives transformed the landscape not only by creating urban centers and by agriculture, but also by fire.

Why have you never heard of the Mississippian civilization? This is the important question. Everyone has heard of the Mayans (the contemporaries of the Mississippians), the Aztecs, and the Incas. But popular racist images show Native Americans north of Mexico as being small populations of hunters and gatherers, leaving scarcely a footprint as they gathered berries and nuts and hunted deer. The reason this image is racist is that it justifies the conquest of North American tribes, who were not using the land to its full capacity, by civilized Europeans who transformed the landscape into a fruited plain with whitewashed cities, a process popularly called Manifest Destiny. What is sometimes called “revisionist history” proclaims the facts about the advanced Native American cultures. But this new view of history is attacked and maligned by conservative state legislatures. There is even a law in Oklahoma that forbids the teaching of any history or sociology that would embarrass white Americans or make them feel inferior.

The conservative racist (these are not necessarily the same things) viewpoint has been triumphant, because if you ask Americans about major precolumbian urban centers north of Mexico, very few will know anything about it. The myth of the savage, vanishing Red Man persists.

Friday, June 2, 2023

Evolutionary Mysteries 2: Why Some Young Leaves Are Red

This week’s evolution video is about why some young leaves are red. You may have noticed that the unfolding leaves on plants as diverse as redbuds and blackjack oaks are reddish—in some cases, as with the blackjack, a brilliant scarlet. This is not true of all plants, but true of enough of them to invite an evolutionary answer.

The leading contender for an explanation is that young leaves are pretending to be dead. A young leaf has its whole life before it. Its entire contribution to the growth of the plant can be threatened by a herbivore eating it. When a herbivore eats an older leaf, however, the plant has less to lose in terms of future growth. The reddish color of a young leaf is a camouflage that makes a healthy young leaf look dead, thus diverting herbivores to the older leaves. This becomes more believable when you consider that many insects would not distinguish between red and brown, the color of plant death. The red color is caused by anthocyanins. They will reduce the amount of sunlight that gets to the chloroplasts, but by the time the leaf is fully grown and ready to produce food, the anthocyanins fade.

While this explanation is the most likely, it is not the only possibility. It could be that the young leaf is vulnerable to harmful ultraviolet radiation, which can cause damage but is outside the range of photosynthetically useful light. The red color, therefore, might be protection from ultraviolet damage.

And there is no reason why both answers could not be true at the same time.

To prove which of these explanations, or any other, might be true would be difficult. It might require breeding plants that produce more or less anthocyanin: young leaves without it, older leaves with it. Actually, some horticultural variants (such as red-leaved redbud trees) have adult leaves that are red (and green at the same time, resulting in a purplish color). Do these reddish adult leaves have less herbivore damage than green leaves? I do not know, but it is possible. Another way would be to compare herbivore damage in red vs. green patches on the same leaf; one study demonstrated that herbivores avoided the red areas ofvariegated leaves.

Keep your eyes open and there are mysteries of nature all around you that cry out for an evolutionary explanation.