An important challenge to traditional (pre-1860) ideas about species was the observation that seemingly dissimilar organisms, such as hummingbirds, humans, and whales, have similar skeletal structures. this most directly suggested to biologists that

Ghana, first of the great medieval trading empires of western africa (fl. 7th–13th century). it was situated between the sahara and the headwaters of the sénégal and niger rivers, in an area that now comprises southeastern mauritania and part of mali.

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Mean is the same thing as averageexamplethe mean of 30 and 40 is 35 because (30+40)/2=70/2=35mean absolue deviation is when you take the mean of the setthen you find the diffference of each number of the set then take the mean of thatex if yo uhave 1,2,3,4,5 and the mean is 3, then ou find the absolute value of the difference of each|1-3|=2|2-3|=1|3-3|=0|4-3|=1|5-3|=2add them and divide by 5(2+1+0+1+2)/5=6/5= mad=6/5