Luria arrived in New York City on September 12, 1940 and soon changed his first and middle names. With the help of physicist Enrico Fermi, whom he knew from his time at the University of Rome, Luria received a fellowship at Columbia University. He soon met Delbrück and Hershey, and they collaborated on experiments at Cold Spring Harbor Laboratory and in Delbrück's lab at Vanderbilt University.
His famous experiment with Delbrück in 1943, known as the Luria-Delbrück experiment, demonstrated that inheritance in bacteria follows Darwinian rather than Lamarckian principles and that mutant genes occurring randomly can still give viral resistance without the virus being present. The idea that natural selection affects bacteria has profound consequences, for example, it explains how bacteria develop antibiotic resistance.
From 1943 to 1950, he worked at Indiana University, Bloomington. His first graduate student was James D. Watson, who went on to discover the structure of DNA with Francis Crick. In January 1947, Luria became a naturalized citizen of the United States.
In 1950, Luria moved to the University of Illinois at Urbana-Champaign. While investigating how a culture of "E. coli" was able to stop the production of phages, Luria discovered that specific bacterial strains produce enzymes that cut DNA at certain sequences. These enzymes became known as restriction enzymes and developed into one of the main molecular tools in molecular biology.
Maya calendar
The Maya calendar is a system of calendars and almanacs used in the Maya civilization of pre-Columbian Mesoamerica, and in some modern Maya communities in highland Guatemala.
It shares many aspects with calendars employed by other earlier Mesoamerican civilizations, such as the Zapotec and Olmec, and contemporary or later ones such as the Mixtec and Aztec calendars. Although the Mesoamerican calendar did not originate with the Maya, their subsequent extensions and refinements of it were the most sophisticated. Along with those of the Aztecs, the Maya calendars are the best-documented and most completely understood.
There are three main Maya calendars: the 260 day ritual calendar called "Tzolk'in", the 365 day "Haab"', and the "Long Count". Approximately 52 years pass before the Haab and Tzolkin calendars converge and are back in the same alignment. This is called the Calendar round. The Tzolk'in is still in use today by the Ixil, Kek'chi and Quiche peoples of the Guatemalan highlands.
Here is an example of a Maya calendar date: 12.18.16.2.6, 3 Cimi 4 Zotz. The “12.18.16.2.6” is the Long Count. Going from right to left, the units are: kin (1 day), uinal (20 kin = 20 days), tun (18 uinal = 360 days), katun (20 tun = approximately 20 years), baktun (20 katun =394 years). The Long Count was used to track periods of time longer than the 52 years of the Calendar Round. The mythical starting date of the current creation was August 11, 3114 BCE (Gregorian). “3 Cimi” is the Tzolkin date. The Tzolkin date is a combination of thirteen days numbered one-thirteen and twenty day-names. “4 Zotz” is the Haab' date. The Haab' year contains 18 months (each named) with 20 days each. The number before the word is the day of that month. The Maya then added five days to the calendar after the last month, Cumku, ends, in order to make the year 365 days long. Those five days, called "Uayeb," were considered to be unlucky.
A common myth about the Maya calendar was that it predicted that the world would end on December 21, 2012. This belief was mistaken. According to the Maya, there were three previous worlds. The first began with “the creation of the Earth, and it had upon it vegetation and living beings. Unfortunately, because they lacked speech, the birds and animals were unable to pay homage to the gods and were destroyed. In the second and third Ages the gods created humans of mud and then wood, but these also failed to please and were wiped out. The "zero date" 13.0.0.0.0 on the Long Count was when, according to the Maya, the third world ended and the fourth one, the current world, began. Another 13.0.0.0.0 would occur on December 21, 2012. There is no evidence that the Long Count would end on 13.0.0.0.0 or that the Maya believed that this would be the date of the apocalypse. Still, a variety of popular books and movies have contributed to the publicity surrounding the Maya calendar's supposed prediction of the end of the world in 2012. Some believershave taken advantage of this publicity to sell guides to surviving the apocalypse.
Mexican coat of arms
The flag of Mexico contains a coat of arms which is derived from an Aztec symbol depicting an eagle with a snake in its mouth.
In the early 14th century, the Mexica people were a wandering tribe looking for a permanent settlement in modern day central Mexico. They survived by hunting and gathering and were often hired to fight as mercenaries for the city-states scattered throughout the region. According to legend, their god, Huitzilopochtli, told them to establish a city of their own at a site where they would find an eagle eating a snake on top of a cactus. The legend relates that the people saw the eagle on a small, swampy island in the middle of the shallow Texcoco lake. The Mexica invented a resourceful system of gardening, called chinampas, which allowed them to grow small gardens, eventually drying out the lake. In 1325, they completed construction of a city there. That city, which they called Tenochtitlan, became the capital of the Aztec Empire, which dominated central Mexico until its destruction by Spanish Conquistadores led by Hernando Cortes.
After winning its independence from Spain in 1810, the newly created nation of Mexico–whose capital was built on the ruins of Tenochtitlan–adopted the symbol of the eagle and the snake to commemorate its Aztec heritage. The symbol can be found at the center of the Mexican flag.
San Lorenzo Tenochtitlan
San Lorenzo Tenochtitlan started out as an agricultural and population center for the Olmec civilization, which inhabited a region of what is today southeastern Mexico. The Olmecs emerged as early as 1500 BC as the earliest complex society in the Americas. San Lorenzo is best known as the first city established in the Americas.
The main reason San Lorenzo flourished at such an early period is its location within the Coatzacoalcos flood plain, which provided fertile land for farming. Thus, the settlement of San Lorenzo follows the pattern of settlement of the world’s very first urban centers, which emerged in the fertile river valleys of Mesopotamia. Because of the high farming value of the surrounding land, San Lorenzo ranked as the Olmecs’ most populous settlement from 1200-900 BC. During that period, San Lorenzo had the biggest trade market in all of the Olmec Heartland.
For unknown reasons, many people migrated out of San Lorenzo in 800 BC to the nearby city of La Venta. However, San Lorenzo was repopulated in 600 BC, when it became a center for Olmec ritual sacrifices until the population faded away in 400 BC along with the Olmec civilization. Today, San Lorenzo remains a significant archaeological site because the artifacts found there–including the famous Colossal Heads and jade masks–shed some light on Olmec culture and its profound influence on later Mesoamerican civilizations, such as the Aztec and Maya.
Terrace farming
Terrace farming (also called step farming) is a method of farming that consists of different "steps" or terraces that were developed in various places around the world. The Rice Terraces of the Philippine Cordilleras (hills and mountains) is a World Heritage Site. It dates back two thousand years.