How much brain is necessary?

[CutterJohn]

http://www.telegraph.co.uk/telegraph/multimedia/archive/00640/news-graphics-2007-_640374a.jpg

This is a picture of the worlds tallest man, Bao Xishun, and the worlds smallest, He Pingping.

He Pingping is, from all accounts, a rather normal person, even runs his own restaurant, yet his head, and brain is at least 5 times less massive than Bao’s(who is also, apparently, a normal person aside from being extremely tall).

I also remember a story from a while back where a guy was missing most of his brain(like 75-90%) due to a tumor or fluid buildup or something, and behaved quite normally.

So, how much brain is necessary, and does having a larger brain even help at all? Could we breed a race of micro humans who behave the same but are just 1/10th size?

[Henrichek]

Interesting question. One thing to consider is that a larger brain is usually necessary for a larger body, other than that I don’t have much to say here. The brain/body mass ratio is sometimes mentioned in animal intelligence discussions.

[Fear_Itself]

Some hydrocephalus patients have less than 5% of normal brain mass, yet score above 100 on IQ tests.

Although anecdotal accounts may be found in medical literature, Lorber is the first to provide a systematic study of such cases. He has documented over 600 scans of people with hydrocephalus and has broken them into four groups:

[ul]
[li] those with nearly normal brains [/li][li] those with 50-70% of the cranium filled with cerebrospinal fluid [/li][li] those with 70-90% of the cranium filled with cerebrospinal fluid [/li][li] and the most severe group with 95% of the cranial cavity filled with cerebrospinal fluid.[/li][/ul]

Of the last group, which comprised less than 10% of the study, half were profoundly retarded. The remaining half had IQs greater than 100. Skeptics have claimed that it was an error of interpretation of the scans themselves. Lorber himself admits that reading a CAT scan can be tricky. He also has said that he would not make such a claim without evidence. In answer to attacks that he has not precisely quantified the amount of brain tissue missing, he added, “I can’t say whether the mathematics student has a brain weighing 50 grams or 150 grams, but it is clear that it is nowhere near the normal 1.5 kilograms.”

[Hari_Seldon]

Homo floresiensis seems to have been a race of humans that averaged about 3 1/2 feet tall, with an estimated body weight of 55 lb, and a brain size of around 380cc, less than 30% the average brain size of H. sap. Yet they appeared to have a human type civilization. See Homo floresiensis - Wikipedia for more details.

It is worth noting that H. Neanderthalis had an average brain size about 10% larger than us. FWIW, my guess is that first we evolved large brains and then new organization of the brain that made size less important. Anthropologists and linguists would give a lot to know what Neanderthal speech (if any) was like.