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Secondary Sexual Characteristics
Primary Sexual Characteristics
Secondary sex characteristics include, for example, the manes of male lions ,  the bright facial and rump coloration of male mandrills , and horns in many goats and antelopes. These characteristics are believed to be produced by a positive feedback loop known as the Fisherian runaway produced by the secondary characteristic in one sex and the desire for that characteristic in the other sex. Male birds and fish of many species have brighter coloration or other external ornaments.
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While primary sex characteristics are those that are present at birth, secondary sex characteristics are those that appear during puberty. These secondary sex characteristics are caused by hormones released at the time of puberty, which usually is around two years earlier in girls than in boys. While both boys and girls grow taller in their teenage years, the male body becomes more muscular, and the shoulders grow broader than the hips, while the female's hips become wider than her shoulders, and breasts develop. Some of the first changes in a boy are the growth of his testicles and growth of pubic hair. Later, the chest becomes larger, hair grows in the armpits, muscles grow in the arms and legs and shoulders become larger and stronger. In some males, hair also grows on the chest, but generally, Asian men are less hairy and less muscular than Caucasian men, and those from Africa have coarser body hair. Facial hair, which usually grows first above the lips and later grows on the cheeks, may grow into a mustache and beard unless the boy shaves regularly. The larynx voice box becomes larger as well, resulting in a deeper voice.
Primary and secondary sexual characteristics refer to specific physical traits that set apart males and females in sexually dimorphic species; that is, species in which the males and females look different from each other. Primary sexual characteristics are there from birth for example, penises vs. Secondary sexual characteristics emerge at puberty such as low voices and beards in human males, and high voices and no facial hair in human females. Primary and secondary sexual characteristics are physical traits that make males and females look and behave differently from each other in certain species, including humans. Secondary sexual characteristics appear during puberty. These characteristics are not used in sexual reproduction, but are important for attracting a mate - such as long tusks or brightly colored scales - or being able to provide care for offspring - such as human breasts or marsupial pouches. The choosy female theory purports that females choose males with bigger, brighter and better ornamentation to increase the viability of her offspring by choosing a mate with good genes. Primary sexual characteristics are those that are present at birth. In mammals, sex is determined through hormonal events in utero that under normal circumstances are controlled by the combination of X and Y chromosomes.