Sunday, October 27, 2013

Hookworms in the Pre-Clovis New World: Keys to Understanding Human Migrations

Hey everyone! Sorry that it's been so long since my last post. This whole month has been a blur of crazy.  On the upside, I went to a conference last week and learned a LOT about human migrations into the New World.  I went as a tag-along with my major professor and a friend. They presented some of their amazing work on parasites from Paisley Cave.  For those of you who don't know, Paisley Cave is an excavation site in Oregon that has some really groovy pre-Clovis human artifacts and remains.  When they received coprolites from this cave, they had expected to find something like an acanthocephalan, but what they found was much, much more exciting.  From these 9,000-year-old coprolites came some of the most beautifully preserved hookworm eggs you've ever seen!

I know what you are thinking...who cares? Right?  (Stop that! This is cool stuff!)  You should all care, and here's why.  Hookworms are tropical parasites....and they were found in Oregon at a site dating back to the days before people developed agriculture in the New World!!!  So now the big the hell did they get there?  Hookworm larvae need a very specific set of environmental conditions to survive.  You see, the life cycle of these hookworms involves adults laying their eggs in the human intestine, which get passed through the feces and into the soil.  Once the eggs finally hatch in the soil (which must be warm and moist), the juvenile hookworms crawl about until they are able to penetrate through the skin of their next host. Because part of the life cycle is dependent on having the proper environmental conditions, it is remarkable to find the eggs of this parasite so far north, and dating back to a time when ice sheets covered much of the northern parts of the continent.

The really cool thing that comes out of all of this is that it challenges our theories about humans walking across the Bering Strait and down through the "ice-free corridor".  Hookworms would not have made this trip because of their environment-dependent life cycle unless humans moved super fast via the predicted route.  However, a coastal migration could explain the continual propagation of these parasites in pre-Clovis humans.  A coastal migration could have moved people faster into the southern parts of the continent.  Between moving quicker down the coastline and the possible formation of microclimates suitable for hookworms (e.g. Paisley Cave with it's hot mess of filth and areas of heat-radiating decomposition), the coastal migration hypothesis seems to make the most sense for why we would find hookworms in Paisley Cave. 

There are also theories proposing a trans-pacific route of migration that is substantiated by craniometric data among other things.  If there is anything to take away from this conference, it is the fact that we don't really know how humans got to this part of the world.  Despite all of our discoveries and investigations, we simply don't know.  However, there is good evidence to support the idea that there were probably multiple migrations into the New World.  It will be exciting to see what we will learn about human migrations over the next few years as more excavations are conducted and more artifacts and remains are analyzed.  I can't wait to see the role parasites will continue to play as we uncover more and more about the story of how we came to populate the Americas.