my @mother= qw( a b d e c g f i h );
my @father= qw( b c a d e f h i g );
my %avgPos;
for my $av (  \@mother, \@father  ) {
    for my $i (  0 .. $#$av  ) {
        $avgPos{$av->[$i]} += $i/2;
    }
}
print " $_ => $avgPos{$_}\n"
    for  keys %avgPos;
my @son= sort { $avgPos{$a} <=> $avgPos{$b} } @mother;
print "( @son )\n";
__END__
 e => 3.5
 a => 1
 d => 2.5
 c => 2.5
 h => 7
 b => 0.5
 g => 6.5
 f => 5.5
 i => 7
( b a d c e f g i h )