Humans are the world’s most dominant species.


I think this is something that most people would agree with, but probably for different reasons. While other organisms may be more numerous (like the Pelagibacter ubique bacteria, thought to number ~10^28 [1]), or contributing more total mass (also probably the Pelagibacter ubique bacteria, which is estimated to have a collective mass more than the sum of all fish in the world's oceans [2]), humans are at the top of the food chain.


It’s not just that we’re smarter than everything else though--it’s that we can do something with the knowledge we have. I don’t mean that in a righteous way. I mean that as humans, we can physically change our environment based on what we learn from the environment. And we can collectively do that to a greater extent than any other species.


The list of physical systems that have some control over their own persistence is pretty short. In fact, it’s a list with one word--and that word is life. Everything else is fully at the whim of its environment. Life persists outside of equilibrium with its environment. If you change an environment slowly enough, life will find a way to ensure its persistence. However, non-living systems will always be moving towards equilibrium.


(E.g. If you changed a frozen tundra to a hot desert slowly enough, polar bears would be able to adapt to their environment in order to persist. Now picture some salt crystals. No matter how slowly you increased the amount of water around the crystals, they would eventually dissolve. Crystals have no control over their own persistence.)


Now, let’s think about how different living systems have different levels of control over their own persistence. All life that we know of is based on the genetic code, and has the ability to genetically evolve over evolutionary time in order to adapt to a changing environment. Alternatively, life can ensure its persistence by moving to a new environment that more closely matches the environment to which it is adapted. Yet a third way for life to persist over time is to create micro-environments. These micro-environments allow organisms to persist in an environment it’s evolutionarily adapted to, within the context larger inhospitable environment.


If an organism’s environment changes quickly (within the lifespan of a single organism), it cannot rely on adapting through genetic change. Instead, the organism must persist through one of the latter two methods described in the paragraph above--by moving to a new environment, or creating it’s own microenvironment.


(E.g. Imagine another polar bear, living on the edge of the arctic circle. The arctic ice sheets are melting, and they’re melting fast enough that the polar bear can’t adapt to it’s current environment through evolution. So the polar bear moves further north in order to persist. But this is only helpful for so long, since the warming is a global phenomenon. If it continues, the polar bears will go extinct because there will be no cold places left to go, and no time to adapt to the new warmer environment.)


Humans do not have this problem. If the world keeps warming, we’ll just create micro-environments (e.g. buildings) that allow us to persist, using technology. Humans, I would argue, are the most dominant species because we can persist through environmental changes that happen on timescales shorter than the lifetime of an individual human, even when the environmental changes are drastic. We can do this because of the micro-environments we can create; our deep understanding of the environment; and the control we have over ourselves and the environment.




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Comment by Kelly C. Smith on May 2, 2016 at 10:12am

Absolutely!  As a philosopher, I like to ask questions that bother people, so I will do that here:  Are life forms with this kind of adaptive ability morally superior to other life forms?  Note that this is not a question about human superiority, since if we take the mission of astrobiology seriously, a "yes" answer here opens up the door to other life forms somewhere else being being able to assert their superiority to us (say, if they have already reached the singularity, etc.) 

Comment by Greg Vance on April 28, 2016 at 1:16pm

I think this post makes a number of good points that have really been lacking in our class discussions so far.  The adaptability of life, especially life on Earth, is a great way to characterize what is and is not alive.  It has a few issues, like every definition of life does, but it has pretty great utility.  In that vein, I enjoy how you demonstrate that the criterion of adaptability can also be used to distinguish different kinds of life from one another into at least two tiers.  This is most certainly a biased statement, but it feels right that we can use it to say that humans are in some way king on this planet.  Sure, Darwinian evolution may not be as universal elsewhere in the cosmos as it is here on Earth, but I see no reason to reject this characterization of life until we have real evidence to suggest otherwise.  It seems natural to say that life adapts and that better life adapts faster, but I have one interesting question: are humans really the most adaptable species on Earth?  Yes, most other macroscopic life would not fare well if their environment changed on the timescale of a couple hundred years, but some bacteria and viruses are far more resilient than that.  Their generations are so brief and their genomes so simple that I would argue have fairly good adaptability on their own evolutionary timescales.

Comment by Charles Wen on April 27, 2016 at 4:08pm

Hello Harrison,

I think your topic is really interesting. I have always been amazed at the degree of change that humans have exhibited on the Earth to make it comfortable. Humans have manipulated the Earth''s resources so much that not only can we survive past the carrying capacity of certain areas, but that we often do so in a pretty luxurious fashion. However, I don't believe that humans will be able to live in luxury forever. Like you said, humans are more than capable of constructing micro-environments, but I don't think that humans will be able to survive through drastic environmental changes unless we can somehow shed our dependence on other types of life. I know little to nothing about ecology, but the one thing that has been drilled into my mind from media regarding climate change is that the fate of ecosystems are heavily intertwined. 

Comment by Jake Hanson on April 27, 2016 at 2:00pm

Hi Harrison,

I like the idea that there is a difference between being intelligent and using intelligence to shape your environment. It is difficult to say which animal or life form is most intelligent because one can argue intelligence is a subjective measure. However, when looking at which life form has influenced its surroundings the most, I think humans are objectively the winner. Whether or not that is a good thing is debatable but at the very least this is a good way to separate humans from other life forms on the planet.

In general, I agree that non-living systems have less control over their own persistence. Typically, a non-living system tries to equilibrate itself with its environment. However, there are non-living systems that perpetuate out of equilibrium. For example, individual stages of the stellar life cycle don't always equilibrate. Rather, the system is cyclic. In this sense, it depends on what scale one is looking at in order to say whether or not a system is in equilibrium. Its possible that there is a connection between life and sustaining disequilibria, but it may be more complex than defining life in terms of it.


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