The higher male IQ can be ascribed to the larger male brain. Three studies have shown that the average male brain size exceeds that of the female brain, corrected for body size. Ankney (1992) found a larger brain size measured by weight of approximately 100 grams. Rushton (1992) found a difference in volume of HOcc and Tan et al. (1999) found a difference among college students in Turkey of 91cc. Ankney expresses the male-female difference as 0.78d (SD units). The correlation of brain size with intelligence is 0.44 (corrected for test reliabil- ity). Hence the predicted male advantage in intelligence arising from a larger average brain size is 0.78 multiplied by 0.44, giving a male advantage of .34J = 5.1 IQ points. This should be considered the same, within the range of error arising from the use of different tests, meas- urement error, and different definitions of intelligence, as the actual male advantages of 4.9 IQ points estimated in Lynn (1999), 5.0 IQ points estimated in Lynn and Irwing (2004), 5.49 IQ points on the ASVAB, 5.55 IQ points found in a Danish sample by Nyborg (2003, p. 212), and 4.3 IQ points found by Colom and Lynn (2004) in a Spanish sample. The average of the four estimates is 5.0 IQ points and should be adopted as the best estimate of the male advan- tage among adults. This advantage is wholly explicable by the larger male brain, as would be expected because males and females experience the same environment and therefore envi- ronmental factors cannot account for the male-female difference. The explanation in evolu- tionary terms for the greater average intelligence of men is probably that in most social spe- cies males compete with one another to obtain female mates and in the evolution of the homi- nids intelligence came to play a significant role in success in this competition. Females do not compete for male mates to anything like the same extent. This would have exerted stronger selection pressure for enhanced intelligence in men than in women.

European-African (Difference in IQ SD Units) Brain Size Difference--1.46 d--Predicted IQ difference-- .69 d--- Actual IQ DIfference---2.1 d

Some of the peoples who colonized the Near East between 100,000 and 90,000 years ago migrated northwards and around 60,000 years ago reached the Caucasus, from which they spread into the Ukraine and then, around 40,000 years ago, into central and western Europe. Other peoples from Southwest Asia began to colonize Southeast Europe from Anatolia. These peoples evolved into the Europeans with their paler skins and, in the north of Europe, their fair hair and blue eyes. The Europeans were largely isolated from the South Asians and North Africans on the south by the Mediterranean Sea, and on the east by the Black and Caspian Seas, the high mountains of the Caucasus and Himalayas, and the Kara Kum desert in present day Turkmenistan. In the last ice age, which lasted from around 28,000 to 10,000 years ago, the winters were significantly colder than those in South Asia with the coldest winter month falling to about -5°C. The terrain in Europe became similar to that of present-day Alaska and Siberia. The north of England, Germany, Russia, and the whole of Scandinavia were covered with a permanent ice sheet and the remainder of Europe was cold grasslands and tundra with a few clumps of trees in sheltered places.

These cold winters must have been the main selection pressure for an increase in the brain size and intelligence of the Europeans that drove the average brain size up to l,369cc and their IQ up to 99. Expressing the increase in their brain size as encephalization quotients (EQ) to control for body size, Cutler (1976) has estimated that pre-Wiirm Europeans had an EQ of 7.3 154 and by the end of the Wiirm glaciation they had an EQ of 8.1. When the ice sheets that cov- ered northern Europe receded by about 10,000 years ago the Europeans with their increased intelligence were able to make the Neolithic transition to settled agriculture. However, despite their high IQ they were not able to develop early civilizations like those built by the South Asians and North Africans because Europe was still cold, was covered with forest, and had heavy soils that were difficult to plough unlike the light soils on which the early civilizations were built, and there were no river flood plains to provide annual highly fertile alluvial depos- its from which agricultural surpluses could be obtained to support an urban civilization and an intellectual class (Landes, 1998). From around BC 2500 the Europeans overcame these prob- lems in the relatively benign climate of southern Europe, where they developed the first Euro- pean civilizations in Crete and Greece. From around BC 700 the Italians began to build a civi- lization that eventually became the Roman empire and by 200 AD embraced the whole of Europe west of the Rhine and included the Danube basin, the Near East, and North Africa. These first European civilizations in Greece and Rome surpassed those of the South Asians and North Africans in science, mathematics, technology, literature, philosophy, and the arts. The western Roman Empire collapsed in 455 AD and European culture suffered a setback in the ensuing dark ages, but from about the year 1000 AD it revived and from around the year 1500 the Europeans became the foremost people in virtually all areas of civilization, as exten- sively documented by Murray (2003).

The genetical processes through which the higher IQs of the Europeans have evolved will have consisted of changes in allele frequencies towards a greater proportion of alleles for high intelligence and probably also through the appearance of new mutations for higher intelli- gence and the rapid spread of these through the population. The probability of new mutations for higher intelligence in the Europeans will have been increased by the stress of the extreme cold to which the Europeans were exposed.

The lower IQs in the range 90 to 94 in Southeast Europe are probably attributable to some gene flow between South Asians and Europeans across the Dardanelles and Aegean, produc- ing a cline of South Asian and European hybrids in the Balkans with IQs intermediate between those of Europeans (99) and South Asians (84). The same cline is present in Turkey where the IQ of around 90 is only fractionally lower than in the Balkans.

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