Monday, November 23, 2009

The Tree of Life

Last week a friend on Facebook had something about evolution in one of his status posts and one of his friends responded with “if we evolved from monkeys, why do we still have monkeys around today?” I’d never really thought about evolution quite that way but it is a logical question. I of course chimed in with my thoughts on it but the question has really stuck in my head. I hope to be able to give a more detailed and thoughtful response here.

Evolution is a very slow moving process. Based upon the brief life-span that humans possess, evolution is mostly imperceptible. For us to begin to see this process at work, we have to looking back into the fossil records. Our closest historic relative is Cro-Magnon man (30,000 – 17,000 years ago) and before them it was Neanderthal (roughly 600,000 – 30,000 years ago). Scientists have determined that they possessed many of the same physical characteristics as modern Homo sapiens. So technically we evolved directly from them, not apes but apes were in our more distant past. Although we went our separate way, both branches are still successfully growing today. Cro-Magnon and Neanderthal were not quite so lucky.

It helps to understand evolution if you think of our past as a tree. Let’s say that single cell organisms are the seeds that grow into the tree, the tree of life. Billions of years ago the single cell organisms began growing and created the first sprig of growth on the tree. As the tree began growing up, the main branch split into two and each branch continued to grow. Once those branches grew out a bit they split again and grew and split and grew until finally it grew into the shape of a full grown tree.

At each of those points where the branch splits into two branches, that is where the DNA mutated for whatever reason it did. Every split of the branches then becomes something slightly different than the branch it grew out of. As the tree grows taller and wider more and more splits form until there is a whole network of branches. Humans would be one of the tiny branches at the very top of the tree. Monkeys and apes would be on a branch very close to ours. Both branches sprout from our common ancestors. Some of the other branches on the tree would have grown in the direction of the flying animals, sea creatures, flora and various land animals. We all sprouted from our single cell ancestors and grew into the amazing creatures that we are today.

The important thing to remember in this is that it is our DNA that is mutating and that mutation is what causes the shift in characteristics of the creatures. The DNA mutation can be caused by any number of factors. DNA can be thought of as our blueprint. It contains all the information necessary for us to grow from the merging of a microscopic egg and a sperm into the trillion celled organisms that we call humans. Our DNA and the DNA of every living creature on the planet is constantly interacting with the environment and adjusting accordingly.

An interesting and current example of this happening is what is going on at the Space Station. Now that we have people staying up there for several months in an environment without gravity, we are able to see changes in them when they return. One of the most noticeable things that NASA is discovering is that the astronauts bone density is severely decreased. When the long-term astronauts return to our gravity based environment, they are often unable to stand because of the changes their bodies have undergone. This illustrates the amazing capacity of our bodies to adjust to a changing environment. Gradually after returning to Earth for a while their bodies readjust and their bone density returns to normal.

It’s important to note that the bodies of just those astronauts are adjusting and not every person on the planet. I say that because it illuminates the evolutionary process even more. When the environment of just a few members of our species radically changed, within months their bodies shifted and adjusted accordingly. This change is certainly not something that the astronauts consciously choose to do so it shows how the DNA responded to the environment and triggered shifts in their bodies. In theory if they stayed up there forever, we would soon see even more physical shifts in their characteristics as their DNA adapted to the new environment. They would become a new branch off of the human branch on the tree of Life.

That is how it happened on Earth billions of years ago. As creatures began moving out across the planet and into the various climates that existed, their DNA responded to the changes and their bodies slowly evolved. Since they were able to stay in those environments here on Earth they were able to grow and evolve over time until they no longer directly resembled their ancestors. This is what contributed to the amazing diversity of life on this beautiful planet…and the various branches on the Tree of Life.

I recognize that for many people evolution flies in the face of the theory of Creationism. I hope to explore that more in coming posts because I believe it actually doesn’t. As with all things it involves a willingness to explore our myths and beliefs and question our understandings…but that is a topic for another day. Until then I invite you to notice how a tree grows. Rather than fight over resources, all of the branches spread out and grow to work for the good of the tree not just for the needs of a single branch.

1 comment:

  1. Don't worry about insulting Creationists. If they can ignore thousands of years of science in favor of tribal writings from 2000 years ago, they're beyond insult. Good post - wonderful thought. Thanks