I think your question makes perfect sence Linus.
Ok, we have established that change within groups is fact. Lets look at the group that gave rise to everything elce... the humble single celled organism.
Now we have our single celled organism most are distinctly 'animal' like in that they don't photosynthasize... however somewhere allong the line there came into things that bridge the gap between plant and animal these are the
Euglenophyta. Euglenophyta are single celled organisms that have both the traits of animals and plants. They move and have 'eye-spots' like 'animals' but they have Chlorophyll like plants, some can eaven catch and eat food as well as photosynthasize.
Somewhere allong the line a small mutation or group of mutations happined where the single celled Protist like the Euglenophyta stoped acting so animal like and started to settle down. After all you don't really need to chase the sun in a treeless world. The sky is open for everyone.
Our early plants started to group together, you have better opportunities in a colony. Thus we get to the simplest of the Green Alge, wich are just that, colonies of single celled plants. From there the tree is just a few hundred million years of baby-steps in evolution down the road.
To get to animals you have the early protists, one group mutated into our Euglenophyta another stayed all 'animal'. Our animal protist also learned at some point that keeping in a colony was a good idea. Again you have some different and 'better' opporttunities in a colony than you do alone. (such as ready supply of mates for gene swaping) Eventually cells begin to depend on one another for survival and begin to take on roles that benifit the entire colony, thus you end up with something like the wierd and all to little studied Placozoa. The Placozoa are the simplest of the multi-cellular animals. They only have 4 'types' of cells compaired to the 10-20 'types' of cells found in Sponges and the 200+ types of cells found in mammals.
From the Placozoa its only a few hundreds of millions of years of 'baby-steps' to get to the elephant :jam:
Remember that just because one population of x mutates into y it doesn't mean that all the x will die out. Mutation happins to individuals not accross the bord with everyone. One individual with a successful mutation will pass that on to most (if not all) its offspring. And so on untill the changes add up enough to make a new 'something'.
hope this helps
wa:do