----------------------------------------------------------------- |MODE| ----------------------------------------|----|------------------- Height of mid-parent| | | | | | | | | in inches |64.5|65.5|66.5|67.5|68.5|69.5|70.5|71.5|72.5 | | | | | | | | | Average height of | | | | | | | | | offspring |65.8|66.7|67.2|67.6|68.3|68.9|69.5|69.9|72.2 ----------------------------------------------------------------- =The Law of Regression.--=It is plain from this table that the offspring of short mid-parents tend to be under average or modal height though not so far below as their parents. Likewise children of tall parents tend to be tall but less tall than their parents. This fact illustrates what is known as Galton's _law of regression_; namely, that if parents in a given population diverge a certain amount from the mode of the population as a whole, their children, while tending to resemble them, will diverge less from this mode. It is clear that the extent of regression is an inverse measure of the intensity of inheritance from the immediate parents; if the deviation of the offspring from the general mode were nearly as great as that of their parents then the intensity of the inheritance must be high; if but slight--that is, if the offspring regressed nearly to the mode--then the intensity of the inheritance must be ranked as low. In the example in question it must be ranked as relatively high. Computations show that as regards stature the fraction two-thirds represents approximately the amount of resemblance between the two generations where both parents are considered. =Correlations Between Parents and Offspring.--=In modern researches the conception of mid-parent and mid-grandparent as utilized by Galton has been largely abandoned. It has been found more convenient as well as more accurate to keep the measurements of the two parents separate and to deal with correlations between fathers and sons, fathers and daughters, mothers and sons, mothers and daughters, brother and brother, etc. Professor Pearson and his pupils have found for a number of characters that the correlation between either parent and children, whether sons or daughters, is relatively close. The correlation between brother and brother, sister and sister, and brother and sister, usually ranges a little higher than the corresponding relation between parents and children.