Ok, but isn't the whole point of evolution theory that all living creatures on earth share one common ancestor? The trunk of the tree, the root of the tree? We all share common DNA, etc. etc. Then if the bacteria reproduce quickly and can show us an example of what maybe happened over millions of years, then shouldn't something a bit more...dramatic have happened?
The fact that they adapted but stayed bacteria says something, I think.
I'm not sure I totally understand your question, but I'll see if I can take a stab at it.
We all do share a common ancestor. I think our last common ancestor was from a couple of billion years ago or so, though, so it is no longer around today. It would have been bacteria-like and have DNA, although more than that we might never know (bacteria -- except when they live in mats or colonies -- don't leave fossils, so it's kind of hard to know.)
Although we don't know a lot about our last common ancestor, we can look at surviving organisms that are alive today and see how we are decended from them. They are also our ancestors. For example, we can look at an animal's DNA and see that it shares some of our DNA. Animals that are very "close" to us evolutionarily and that came from us not that long ago have DNA that looks really similar. For example, I think orangatangs have DNA that is 97 or 98 or something percent similar to ours (ETA: I am NOT an expert on orangotang DNA
). Basically, we would have to look at a hundred proteins on DNA to tell whether we were looking at a primate or a human! It really is quite amazing. The "code" that tells our bodies how to make a fetus is almost the same as the code that tells a orangatan's body how to make an orangatang fetus (apparently, I don't know how to spell orangotang according to my spell checker
)
For the second part of your question, the answer is a bit more complicated. Organisms don't evolve a lot when they don't NEED to evolve. For example, you could take a colony of eels or worms or bacteria or whatever and put them in surroundings that are very good for them, where they always get enough to eat and they are comfortable and healthy. Even if we were able to look at them over a very long time period, they might not evolve much. You would get some random mutations and some very minor mutations, for example some bacteria might figure out how to get a tiny percentage point more nutrition from sugar, and that evolution would propagate. But really the bacteria or whatever would not change much. Now, if you put them in surroundings where it was hard for them to survive -- maybe they don't have enough food, it's too cold for them, they get diseases, whatever, then they will begin evolving very rapidly.
The reason is that that is what natural selection is -- the organisms that do better (have more offspring) propagate their DNA, and the ones that struggle don't get to propagate their DNA. Over time, you get a bunch of organisms that have the DNA that tends to help them survive. There is a lot of pressure when the environment is not good -- when the organisms are doing just fine -- they're in the right "niche", they are not going to change a lot. Historically, we think that a lot of new species and rapid evolution happened when a colony of organisms got into an environment where it was hard -- imagine some eels living in a stream that gets colder because of the ice age or some bacteria that move into a trench in the ocean or primates that start getting killed off by a new disease. These are all pressures that push groups of organisms to start changing faster than they would normally.
Now ... to venture a bit into what I think you're trying to ask -- why if everything is always evoloving and changing, do we still have "primitive" organisms? Why are bacteria still around? The reason is that organisms evolve when they need to., but when they don't need to, they tend to stay sort of the same. And they don't all evolve at the same pace. A group of organisms -- that colony of eels in that one stream -- might start evolving rapidly because their stream is cool. Their brother and sister eels in the lake which stays the same temperature tend to not evolve much. Over a long period of time, the eels in the stream are really different -- they're no longer brothers and sisters to the eels in the lake. They might even be a new species! But the eels in the lake -- they're already evolved for their niche. They like it there. They're going to stay that species of eel for a long time.
Again, add time and stir, and that is why we might see bacteria AND monkeys. Monkeys evolved from bacteria, but that doesn't mean bacteria go away. Everything is always evolving, but there is still a "niche" for bacteria --- most are happy in their environment. They're evolving, just like we are, just like everything is, but often times they're evolving to process sugar better or have thicker flagella (string like fillaments that help them move around) or have more hardy membranes or whatever it is that makes the bacteria happy
. All this is evolution, too, and we say that bacteria are "evolved" and not really "primitive" because they are doing a great job of continually doing better in their ever-changing environments.
That's a stab at it.... hope that makes sense. Good question.
)
At least we can agree on that!
