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Sexual dimorphism is the condition where sexes of the same species exhibit different morphological characteristics, including characteristics not directly involved in reproduction. [1] The condition occurs in most dioecious species, which consist of most animals and some plants.
Examples of secondary sex characteristics in non-human animals include manes of male lions [4] and long feathers of male peafowl, the tusks of male narwhals, enlarged proboscises in male elephant seals and proboscis monkeys, the bright facial and rump coloration of male mandrills, horns in many goats and antelopes, [10] and the swollen upper ...
Male primary sex characteristics are the penis, the scrotum and the ability to ejaculate when matured. Female primary sex characteristics are the vulva, vagina, uterus, fallopian tubes, cervix, and the ability to give birth and menstruate when matured. [1] Hormones that express sexual differentiation in humans include: estrogens such as estradiol
Homosexual behaviour is demonstrated by 120 known species of birds. [40] While an uptick in research on bird homosexuality – and animal homosexuality in general – has been coming out in recent years, it is common for some authors to labour in articulating the view any root cause or function of bird homosexuality is poorly understood.
Extant primates exhibit a broad range of variation in sexual size dimorphism (SSD), or sexual divergence in body size. [4] It ranges from species such as gibbons and strepsirrhines (including Madagascar's lemurs) in which males and females have almost the same body sizes to species such as chimpanzees and bonobos in which males' body sizes are larger than females' body sizes.
Intersex is a general term for an organism that has sex characteristics that are between male and female. [1] It typically applies to a minority of members of gonochoric animal species such as mammals (as opposed to hermaphroditic species in which the majority of members can have both male and female sex characteristics). [2]
Elephants can use their ears as threat displays in male-to-male competition. Sexual selection in mammals is a process the study of which started with Charles Darwin's observations concerning sexual selection, including sexual selection in humans, and in other mammals, [1] consisting of male–male competition and mate choice that mold the development of future phenotypes in a population for a ...
The social sciences sometimes approach gender as a social construct, and gender studies particularly does, while research in the natural sciences investigates whether biological differences in females and males influence the development of gender in humans; both inform the debate about how far biological differences influence the formation of ...