Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 11/03/84 (WLS Mods); site escher.UUCP Path: utzoo!watmath!clyde!cbosgd!ihnp4!mhuxn!mhuxr!ulysses!allegra!princeton!astrovax!escher!doug From: doug@escher.UUCP (Douglas J Freyburger) Newsgroups: net.sci Subject: Re: darwinism Message-ID: <34@escher.UUCP> Date: Sun, 23-Jun-85 18:08:29 EDT Article-I.D.: escher.34 Posted: Sun Jun 23 18:08:29 1985 Date-Received: Tue, 25-Jun-85 02:37:17 EDT References: <783@oddjob.UUCP> Distribution: net Organization: NASA/JPL, Pasadena, CA Lines: 54 > For some days the following question is bothering me. If the evolution > theory is right, then why the human brain evolved to about six times > as that of an orung-otung and yet human uses only about 5 percent of the > brain cells? If the other cells were not needed then why produce them? Does I have followed parts of the discussion about percentage of brains cells used, but I have three other suggestions as to why humans have such large brains. 1) Humans have very long lifespans compared to other creatures (mammals) of similar mass. This is also in terms of "heartbeats per life" since the heart rate typical of a species is related to its typical mass. Most mammals live to a maximun of about 10^9 beats, but that's between 25 and 30 years for a human. Anyways, since humans live very long, and since brain cells stop replicating very early on in most (all?) mammal species, we need the extras so our elders don't get feeble quickly. Then, having experienced elders as knowledge stores, tribes with the trait tended to survive better. I remember reading something like this in a physical anthropology text, but it was written in terms of language and intelligence. It sounds reasonable phrased either way. 2) There could be some sort of "critical mass" required for a typically human task, like complete language, or tool making, or something. I know there are arguments of what a "typically human task" is, but you still get the idea. I've used Z80 and Vaxen before, and there are programs that simply can't be run on the smaller machine's address space. It could be a similar situation with humans versus orangutangs. I don't think the number of neurons is linear with brain mass or volume, or that its linear with processing power either. Still there might be some sort of threshhold involved. 3) The specialization of the human brain involves most of its mass being in the cerebrum (the part on the top if I got the name wrong). That part is a new invention in evolution. Since it is so new, it is probably done brute-force. Other creatures have had plenty of time for their systems to be incrementally optimized by evolution, but humans have had less than a million years (or less than five million, depending on where you start using the word "human"). Ants and bees have been around for N times that long, and they get along with VERY few neurons. If this is the case, I hope our incremental optimization involves more functionality instead of less mass for the same functionality. I don't really want to end up in the sort of efficiency trap that the ants did. Doug Freyburger JPL 171-235, Pasadena< CA 91106 DOUG@JPL-VLSI, doug@aerospace, ...trwrba!escher!doug, etc.