> But gene clines exist:
> http://en.wikipedia.org/wiki/Image:Cavalli-SforzaMap.jpg
>
> Human groups differ in many ways, and different genetic diseases
> cluster in different frequencies in different human populations.
>
> Humans form ingroups and outgroups readily. Me against my brother, me
> and my brother against my cousin, me and my cousin against the world.
> See, ingroup amity and outgroup enmity since the beginning of human
> history.
>
> Egalitarians will always fight an uphill losing battle. Afterall you
> can blend in all the races, but clines still exist. Look at Brazil.

Funny that you should refer to Cavalli-Sforza's book, which concludes that 
raciation fails when applied to humans. the map is quoted from the section 
where C-S tries to define human races, only to conclude that it is 
impossible.

The concept of "race", when applied to humans, is an ideological one, and 
not a scientific one.
Raciation cannot be applied to mankind because of the lack of homogeneity : 
the necessary factors which are used to define races to do not converge 
enough to define a "race". And they *do not* match physical criteria : the 
concept of a "caucasian" race is as worthwhile as that of a "green eyed" 
race...
An example :  genetic distance between 2 french population groups is only 
*inferior" by 15 % to the distance of 2 other populations chosen *at random* 
throughout the world. Subdivision into "races" are based only on criteria 
and exclude taking in the genetic diversity which characterises the human 
species. Human population went through a phase when only aroud an estimated 
30 000 individuals were left on the entire planet. All modern humans come 
from that stock...
Racial subdivisions used are arbitrarily defined, based on ideological 
reasons or reluctance to give up the mental comfort of a logic of 
classification.

Cavalli Sforza, in the quoted book you mention in your post, offers a 
definition of "human races" *only* to demonstrate that it NOT APPLICABLE, it 
doesn't work, for geneticians and anthropologists. Cavalli Sforza's 
conclusion is, i translate " all attempts at classification of mankind into 
races are arbitrary and prove impossible". Read the book ( Genes Peoples and 
Languages) it's well worth it !

Now off course cultures exist, but that's another story

b