Quote:
Ellie Arroway wrote
Okay, I'm pretty new to Biology. I remember being totally disinterested in high school but I'm going back to school to study anthropology (possibly biological anthropology if I'm smart enough  )
So, since I'm already 38 and would like to get my B.S. quickly so I can move on to my Masters I'm going to take the CLEP for Biology and as many other courses I can.
That being said, I've got a Self Teaching Guide for Biology and I also go an Evolution textbook from Barnes and Noble. I have to read everything 2 or 3 times to really grasp it but it's really remarkable and fascinating. I wish I had got into this stuff back in high school. I was too busy chasing boys and smoking weed though 
What I don't really understand is how a common ancestor could give rise to so many varied animals. I understand that we're all distantly related and DNA tells us this. I just don't see how you go from fruit fly to human ( I know it didn't happen exactly like that but you get my point). I can see species changing but how do you start with ONE type of bacteria to get an animal and then all the different classes and phylum, et cetera?
Please help! |
It is amazingly elegant. For example all dogs are directed (artificial selection) evolution applied to Wolves over a span of a few thousand years. See the incredible variety obtained in such a short time. There are still Wolves because species do not "turn into" other species, they split like the branches of a tree.
In general a new species begins when part of an existing population of critters is somehow prevented from mixing with the rest (isolated, e.g. by Geographic barriers like rivers or mountain ranges). Then the natural variation of individuals within the two populations have no way to average back into the whole group. When the accumulated differences are great enough, that is, when the two populations have diverged too much for them to interbreed any more, you now have two species where once there was just one. Of course, in the natural world, this takes upwards of millions of years just because the selection process is slow and wandering.
As long as there is enough time (like a couple Billion years), the process of evolution by natural (and likely sexual) selection, can achieve incredible complexity, all from trying to survive in the changing environment, and it is all done without the ham-fisted intervention of a celestial blow-hard.
Remember that, once we (creatures) invented sex, we were no longer slaves to mutation for our only variation. We could evolve that much faster which can mean the difference between species survival or extinction when changes in the environment happen quickly.