[timmaxw]

> evolution of the brain always happens by modifying the existing structure

Hmmm, my impression was that evolution took an existing structure and stuffed a bunch of new functionality into it, making it much larger and more complicated. Although the structure already existed in some form, it didn't have the same function. I think it's reasonable to think of this process as "adding" something, even if the structure itself is not entirely new. And human brains pretty clearly _are_ more intelligent than reptile brains!

Here's an analogy: Ancient organisms had light-sensitive "eyespots", and many of our distant cousins on the evolutionary tree (e.g. present-day flatworms) still have eyespots. Evolution gradually modified these existing structures into eyes. I think it's reasonable to think of eyes as a "new" organ that humans have and flatworms don't; and our eyes are clearly superior to flatworms' eyespots.

[overgard]

Evolution and adding complexity aren't the same thing. For example, evolution can also work in reducing complexity. Animals that spend generations living underground in caves will lose their eye sight over a long enough time period.

Point being its not about adding, it's about adapting

[timmaxw]

In _this_ case, the case of the human brain, I think it's fair to say that evolution started with the reptile brain and added something (even if that "something" is "new function and complexity" rather than "a completely new physical structure").

I agree there are other cases where evolution removes/simplifies things. Evolution is adaptation, and that adaptation can consist of adding, changing, and/or removing.

[tsimionescu]

Eyes are far superior to eyespots in certain ways (accuracy, for one), but far inferior in others (energy consumption, size, durability). They are newer than the eyespots of the last common ancestor, but they could well be older than the eyespots of some flatworm species alive today.