Biology Rewriting History

The mitochondria; primary function being producing ATP energy for the cell.  The mitochondria contains circular DNA which is only passed down from the mother.

In the news this past week I have come across two instances where biology has recently rewrote history.  The first and most publicized story has to do with the discovery of Great Britian's King Richard III  (Click for news story here).  Scientists, through the use of forensic skeletal evidence were able to show the skeleton in question had similar features to what history tells us about the king.  The final and most absolute evidence came in the form of mitochondrial DNA.  The mitochondria is an organelle within cells that produces ATP energy for running the cell.  The mitochondria contains a relatively small amount of DNA that is circular in shape.  This DNA is unique in that it is independent from DNA contained within the nucleus of the cell and that it is only passed down from the mother and not the father.  DNA in the nucleus is a combination of half coming from the father and half from the mother, so the offspring is a unique combination of DNA from both parents.  With DNA of the nucleus, every individual person has a unique combination of DNA, except in the case of identical twins which have identical DNA.  In mitochondrial DNA, all offspring have identical DNA to their mother, even if they have different fathers.  In the case of King Richard III, a direct match of mitochondrial DNA was found between the skeleton in question and a present day descendant of King Richard III's sister.  So to break this down, King Richard and his sister would have had identical mitochondrial DNA because they had the same mother.  Identical DNA would have then been passed down through the maternal side of all of King Richard's sisters descendants.  To find a direct match in mitochondrial DNA is undeniable evidence that two people are directly related to each other and that the skeleton must be King Richard III.

The second and far less publicized story has to do the Mary Ingalls, the sister of Laura Ingalls Wilder wrote the "Little House on the Prairie" books.  The question being asked about Mary Ingalls in this investigation was why really did Mary go blind (Click for news story here) .  In the books, Laura claims that Mary went blind as a result of scarlet fever.  With modern medicine we know that scarlet fever rarely causes blindness and if it does the blindness is only temporary.  So the idea that scarlet fever cause blindness is only a myth from the past.  A medical doctor examining this went through the many letters and writings of Laura Ingalls-Wilder in order to find what illness may have actually caused Mary's blindness.  In the letters, the doctor came across what appears to be Mary having spinal meningitis, which causes swelling of the central nervous system.  This swelling could have easily caused damage to the optic nerves and therefore causing blindness. 

Legumes: Self Fertilizing Plants

The green stem of the legume palo verde tree in the Sonoran Desert.

Determining how to fertilize a plant can be quite the difficulty.  You may have heard that most people over water their plants, but it is also true that most people over fertilize their plants.  Certain plants however never need to be fertilized simply because they have "figured" out a way to fertilize themselves.  Bean plants, also called legumes, form a symbiotic relationship with a bacterium known as rhizobium.  The air we breath is about 70 percent nitrogen, an essential nutrient for plant fertilization.  Atmospheric nitrogen however cannot be used by plants, it must be converted into a different form called ammonium.  Rhizobium bacteria has the ability to take nitrogen gas and convert it into ammonium.  This changing of nitrogen gas into ammonium is known as nitrogen fixation. 

Using legumes in the garden can be quite a useful way to fertilize your plants naturally.  Farmers in the Midwest will often alternate between corn and soybeans, taking advantage of the fact that soybeans naturally replenish the soil with nitrogen fertilizer that the corn can use.  In deserts, which have soils that are naturally deficient in nitrogen, plants must either be adapted to living in soils with low nutrients or have the ability to fix their own nitrogen.  For this reason, legumes are extremely common in desert ecosystems.  Legumes are not just your typical bean plant, they also grow into bushes and trees.  In the Sonoran Desert palo verdes, mesquites, ironwoods, and acacias are all small legume trees that form bean-like pods.  Typically, these legume trees will form islands of soil under their canopy that are rich in nutrients compared to soils beyond the canopy.  Because of the slightly richer soil many smaller plants will often be growing in this micro-environment. 

The darker growths on these plant roots are tumors infected with rhizobium bacteria.

Legumes and Rhizobium bacteria form their association with each other in the soil-root environment.  Rhizobium are naturally occurring soil bacteria but don't really do much if they haven't infected a legume.  When bean seeds germinate and begin to grow, rhizobium already present in the soil infects the new plants roots.  Points of rhizobium infection in the roots form into tumorous-like growths which are like little nitrogen fixing factories.  Typically we think of tumors as unhealthy but be assured, this type of plant tumor is very healthy and beneficial to not only the infected plant but also to the entire environment.  Legume plants that for some reason are not infected become extremely anemic with stunted growth and yellow coloration. 

Tuzigoot National Monument

Desert grassland surrounding the Tuzigoot ruins.  National Parks website photo.

When it comes to living off the land as the ancient Sinagua Native Americans did, Tuzigoot National Monument near Cottonwood, Arizona has it all.  Landscape diversity is essential when it comes to finding the products essential for life and Tuzigoot is especially rich when it comes to the landscape.  Think about it.  If you were to live off the land and not be required to wonder around searching for things constantly you would need a variety of different types of habitats that support a variety of different types of plants and materials necessary for life.  You would need food, building products for shelter, material for clothing, and water at least.  At Tuzigoot, all of these things are highly concentrated in a relatively small area. 

If you visit Tuzigoot National Monument you can see four major habitats that would have provided nearly everything the ancient Sinagua's would have needed within about 50 acres, which is about the size of a very small farm.  Tuzigoot is located in the desert grasslands of the Upper Sonoran Desert.  The desert grasslands surrounding these ruins would have provided yucca plants which provided some fiber and some food for the Native Americans.  Food would have been in the form of plants such as cacti fruits that could have been gathered or animals for hunting.  The desert grasslands are the least productive habitats though of this area.  Even more productive would have been the mesquite and acacia bosque downslope and closer to the river and wetland.  This thick brushy habitat grows where soil moisture is higher than in the grasslands and where the river has deposited deep soils.  The mesquite trees provide huge amounts of food in the form of mesquite beans every summer.  These bean pods were ground-up and made into cakes.  Mesquite wood also provided materials for building and tools.  The deep soils of the mesquite bosque are also likely where farming took place.  Of course, farming in these areas provided food mostly in the form of corn, beans and squash, but it also provided cotton to make clothing.  The mesquite bosque was also a great place for animals to hide and was therefore very good for hunting. 

Tavasci Marsh. Photo from National Parks website.

Slightly down slope from the bosque two extremely important habitats can be found.  The first is the large marsh.  The marsh is today known as the Tavasci Marsh and is dense with grassy wetland plants.  The marsh would have provided essential habitat for all kinds of animals that came to it for both water and food, both of which were scarce in the surrounding desert grasslands.  The Native Americans would have used the marsh as a hunting area as well as an area to gather food from plants.  For example, the cattails in the marsh provide huge amounts of potato-like food in their root systems.  Lastly, the perennial flowing Verde River would have provided trees for building materials, water to drink and for watering plants, and wildlife for eating.  Across all of these habitats there of course can be found an abundance of rocks that the Sinagua used for building.