Females with a twin or very close-in-age brother, sometimes view him as their male alter ego, or what they would have been like, if they had a Y chromosomes. Fraternal relationship
The book Nicomachean Ethics, Book VIII written by Aristotle in 350 B.C.E., offers a way in which people should view the relationships between biological brothers. The relationship of brothers is laid out with the following quote: 
"The friendship of brothers has the characteristics found in that of comrades and in general between people who are like each other, is as much as they belong more to each other and start with a love for each other from their very birth, and in as much as those born to the same parents and brought up together and similarly educated are more akin in character; and the test of time has been applied most fully and convincingly in their case". For these reasons, it is the job of the older brother to influence the ethics of the younger brother by being a person of good action. Aristotle says "by imitating and reenacting the acts of good people, a child becomes habituated to good action". Over time the younger brother will develop the good actions of the older brother as well and be like him. Aristotle also adds this on the matter of retaining the action of doing good once imitated: "Once the habits of ethics or immorality become entrenched, they are difficult to break."
In the paired ventral part of the fin line, normally only the pectoral and pelvic fins survive (but the Devonian acanthodian fish Mesacanthus developed a third pair of paired fins); but along the non-paired parts of the fin line, other fins develop. In tetrapods, only the four paired fins normally persisted, and became the four legs. Notomelia and cephalomelia are atavistic reappearances of dorsal fins. Some other cases of polymelia are extra development along the paired part of the fin lines, or along the ventral posterior non-paired part of the fin line. Notable cases
Humans
1995: Somali baby girl born with three right arms. In the summer of 2005, a baby girl named Destiny was born with a fully formed extra leg in Detroit. This was the result of a conjoined twin scenario. In March 2006, a baby boy identified only as Jie-jie was born in Shanghai with a fully formed third arm: he had two full-sized left arms, one ventral to the other. This is the only documented case of a child born with a fully formed supernumerary arm. It is an example of an extra limb on a normal body axis.