Chapter 1: Originating in Disequilibrium
In this chapter the question of life's origin is explored. All life is sustained by a 'main reaction' which cannot be explained by the combination of organic molecules that created some sort of primordial soup. Rather, one of the first clues to the origin of life was offered by Darwin's stomping grounds: The Galapagos Islands. In 1977, scientists began to explore the abundance of bacterial life in hydrothermal vents existing in the depths of the ocean (population densities in this extreme environment compare to those of the rainforest). The interface between hydrothermal vents and the ocean creates a beautiful disequilibrium that gave rise to life.Click Here for Cool Photos of Vent Organisms
LUCA (last universal common ancestor) is said to be one of these early microbial life forms occupying hydrothermal vents billions of years ago. Due to the alkaline conditions of the vents and the acidic conditions of the oceans, a natural proton gradient was established. Life could not leave the vents until it was able to create its own electrochemical gradient through a reverse Krebs cycle (also known as the process of chemiosmosis), where organic molecules and ATP are generated rather than consumed. This theory suggests that LUCA was a porous rock that generated complex energy molecules due to gradients established by an environmental disequilibrium.
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"These mechanisms evolved by natural selection, there is no doubt". I like the author's search for LUCA and how he addresses all current theories of life's origin and then interprets them analytically. I think it is interesting to consider LUCA as arising from state of interaction with matter and preset environmental conditions. So far, the author seems to be leaning toward explaining evolution in a purely adaptationist view.
However, the little I have learned from Penelope Boston's lecture suggests that Microorganisms have a relatively fast rate of evolution. Bacteria is able to freely exchange genetic material through horizontal gene transfer and also has a high mutation rate. The combination of these evolutionary conditions contribute to swift evolution. In order to quickly respond to environmental stresses, natural selection alone cannot explain the genetic variation and abundance of microbes occupying the planet today. I am interested to see how the story may change when discussing the arrival of DNA in the following chapter.
Hey Haley!
ReplyDeleteI also enjoyed the search for the LUCA in this chapter because it showed a different perspective on how life may first have formed. In the search for the last universal common ancestor we are able to learn and discover more about how life first evolved...this is what I found most interesting. I did not expect for Lane to go as far in depth as he did in this chapter to explain multiple theories for how life may have evolved...this was another aspect that I found interesting in the reading.
I agree with you Hayley in saying that natural selection cannot produce the variation of life we see today. In this beginning stage of life there must have been a huge amount of random variation as DNA was just beginning to come together as a molecule and the basic structures of life were being assembled. A question for both you and Celina would be do you think natural selection had a role in creating DNA at this stage as in how do you select based on genes when genes are not even fully developed?
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