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Inter-sexual selection
In many species the males look different to their female counter parts, they have a tendency to be more elaborately coloured. This is how they attract females to them and not other males. A good example and classic example of males looking more attractive than the females is peacocks, with their beautiful and big tail feathers.
The male African Paradise birds ( Vidus paradisea ) have big beautifully coloured tails, but it is a handicap to them; because it is so big and heavy it gets caught easily. Amo Zahavi said that it is a handicap to the males but because of it the males must be more tough and robust to be able to survive with the tails.
Robert Fisher came up with a more plausible explanation in that if a female mates with an attractive male, she will have more attractive babies (males), which in turn will attract more females; evolution will end up running away for selection of more attractive males. A man called Andersson in 1982 did an experiment that very nicely showed Fischer's hypothesis; he set up 9 groups of 4 male long-tailed widow birds ( Euplectes prongue) , each matched for territory quality and tail length. He took one male at random from each group and cut the tail to 14cm. the piece removed was then glued to another random male in the group. The other 2 acted as controls, but one had it's tail cut and stuck back on .
He counted the number of nest in each territory; prior to the manipulation all males had on average 1.5 nests in their territory. After the manipulation, males with shortened tails averaged only 0.5 nests in their territory; males with lengthened tails averaged 2 nests in their territory. From this he decided that the females must favour the males with artificially lengthened tails.
