Thursday, April 26, 2012
There are thousands of mythologies that explain how life was created and got onto the earth. Just about every group of people that ever lived made up some explanation about the creation of life. Because their memory of history only extended back to the memory of the oldest living person in the tribe, they had no perspective on how the Earth had changed on vastly longer time scales. Memory can only last as long as someone remembers the story. And as anyone knows that has ever played a game of telephone, the story grows in the telling. The big points stay similar, but the details are filled in.
These creation stories were comforting for the people who shared them. But as the dark ages ended Europeans began to chart the course of the stars in the heavens, systematically dig into the earth, began to explore the world on ships, and most importantly of all, began to methodically record the information they were finding, and sharing this information with others. The information they were finding didn't match the creation myths to this point. Instead of the Earth being thousands of years old, life was millions of years old, and then billions of years old. Instead of the Earth being the center of the universe, the Earth circled around the Sun, and it wasn't even the biggest planet.
This new evidence completely disproved all the ancient myths. The old ways of thinking were so entrenched that anyone who disagreed with them was stoned or burned to death. A new more systematic way of asking questions about everything was developed called “The Scientific Method.” This allowed people to ask questions about the universe and experiment to see if the question was true or not. Instead of taking things on faith this new method required people to repeat the experiment before they accepted the theory as true. And new theories could be presented to refine or replace older theories, without anyone being burned to death.
Many theories were proposed that explained bits and pieces of the theory of life. One theory took precedence over all the rest. A man named Darwin took a voyage on a ship and studied a group of islands with an amazing diversity of life. He noticed many patterns and over the course of years he worked on a book. Another man named Wallace independently came up with nearly identical theories to Darwin. So Darwin was forced to abandon work on his masterwork book and immediately publish a pamphlet called, “On the Origin of Species.”
It took decades of experiments to prove this controversial work to be correct. A combination of the study of fossils and looking at living species. Over the years since then the theory has been refined, but never disproven.
The way evolution works is that living populations have environmental pressures. Their offspring will either be fit to survive in that environment or not. Because there are limited resources the offspring that can get the most resources and have the most offspring will have the most descendants, crowding out the less fit. This pressure from other species and your own species is a form of environmental pressure as well.
It is important to realize that individuals in a population do not evolve. The offspring of a pairing can have a lot of different combinations of genes, which make them more or less fit. Sometimes there is an error when the DNA is duplicated. Most of the time this causes the offspring to be completely unfit. But the mutation can result in an individual that is more fit for the environment it finds itself in.
The pressures of all the species in an area all evolving together is called macro-evolution. When one species becomes more fit for the environment it puts more pressure on the other species competing for the same resources.
A new species forms when individuals from the same species stop breeding together, either because of behavior changes, or because of geographic separation. At some point in the future the small changes accumulate or the number of genes changes and makes it impossible for the individuals to breed together anymore.
We talked about theories about how life evolves, but where did life originally come from? Nobody knows for sure, and it is impossible to prove one way or another. The most popular theory is that the early atmosphere rained out organic compounds into the early seas and ponds. Then primitive replicating molecules began duplicating. Eventually a cell wall was formed by mistake, this became the primary cell that out competed all the existing self replicating molecules.
This cell replicated itself and mutations caused it to fit into every available ecological niches. Cells began to invade other cells in parasitic relationships. Eventually these relationships became symbiotic and beneficial to both cells. This happened several times; once with mitochondria, a second time with the nucleus replacing previous, and a third time with chloroplasts. This increase in complexity allowed the development of multi-cellular life. This multi-cellular life got washed up onto land during high tide, became adapted for land bit by bit, and then spread from the shore inland.
If you look at all the stellar systems in our galaxy, and all the galaxies in the sky, the odds that life evolved on more than just one planet is almost a certainty. Even if you say that only 1 in a million suns has a planet in the right place, and 1 in a million of those planets develop life, that still leaves millions of places that life could develop. And life may just be completely adaptable so that it can form in conditions well beyond what we expect, including in interstellar space far from any sun. We have found life on Earth in ice fields, miles deep in the earth, miles deep under the ocean around volcanic vents, in hot springs, and even in nuclear reactors. It may be possible that the first life on Earth came from the comets that rained down onto the forming planet.