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A few types of organisms, such as many fungi and the ciliate Paramecium aurelia, [11] have more than two "sexes", called mating types. Most animals (including humans) and plants reproduce sexually. Sexually reproducing organisms have different sets of genes for every trait (called alleles). Offspring inherit one allele for each trait from each ...
Regarding sexual dimorphism (see the section about animals above), humans are in the intermediate group with moderate sex differences in body size but with relatively small testes, [10] indicating relatively low sperm competition in socially monogamous and polygynous human societies. One estimate is that 83% of human societies are polygynous, 0 ...
Human reproduction naturally takes place as internal fertilization by sexual intercourse. During this process, the man inserts his erect penis into the woman's vagina and then either partner initiates rhythmic pelvic thrusts until the man achieves orgasm , which leads to ejaculation of semen containing sperm into the vaginal canal.
In order to reproduce sexually, both males and females need to find a mate. Generally in animals mate choice is made by females while males compete to be chosen. This can lead organisms to extreme efforts in order to reproduce, such as combat and display, or produce extreme features caused by a positive feedback known as a Fisherian runaway.
Gestation, called pregnancy in humans, is the period of time during which the fetus develops, dividing via mitosis inside the female. During this time, the fetus receives all of its nutrition and oxygenated blood from the female, filtered through the placenta , which is attached to the fetus' abdomen via an umbilical cord .
In this method, however, all eggs in a clutch (20–50) will be of the same sex. In fact, the natural sex ratio of this species is five females to one male. [17] In birds, mothers can influence the sex of their chicks. In peafowl, maternal body condition can influence the proportion of daughters in the range from 25% to 87%. [18]
Human reproductive ecology is a subfield in evolutionary biology that is concerned with human reproductive processes and responses to ecological variables. [1] It is based in the natural and social sciences , and is based on theory and models deriving from human and animal biology, evolutionary theory , and ecology .
In advanced groups of insects, the male uses its aedeagus, a structure formed from the terminal segments of the abdomen, to deposit sperm directly (though sometimes in a capsule called a "spermatophore") into the female's reproductive tract. Other animals reproduce sexually with external fertilization, including many basal vertebrates.