This is not what the data suggest. From the wiki article: adoption studies show that by adulthood adoptive siblings aren't more similar in IQ than strangers (B

This is not what the data suggest. From the wiki article: adoption studies show that by adulthood adoptive siblings aren't more similar in IQ than strangers (Bouchard 1998), while adult full siblings show an IQ correlation of 0.6. An interesting survey summary of the studies by Kaufman 2009 of IQ correlation between groups: * Same person (tested twice) .95 * Identical twins—Reared together .86 * Identical twins—Reared apart .76 * Fraternal twins—Reared together .55 * Fraternal twins—Reared apart .35 * Biological siblings—Reared together .47 * Biological siblings—Reared apart .24 * Unrelated children—Reared together—Children .28 * Unrelated children—Reared together—Adults .04 * Cousins .15 * Parent-child—Living together .42 * Parent-child—Living apart .22 * Adoptive parent–child—Living together .19 This also seems to support genetic heritability being large and environmental heritability being small (and almost insignificant by adulthood).