Female cats are seasonally polyestrous, which means they may have many periods of heat over the course of a year, the season beginning in spring and ending in late autumn. Heat periods occur about every two weeks and last about 4 to 7 days.[149] Multiple males will be attracted to a female in heat. The males will fight over her, and the victor wins the right to mate. At first, the female will reject the male, but eventually the female will allow the male to mate. The female will utter a loud yowl as the male pulls out of her. This is because a male cat's penis has a band of about 120150 backwards-pointing penile spines, which are about one millimeter long;[150] upon withdrawal of the penis, the spines rake the walls of the female's vagina, which is a trigger for ovulation. This act also occurs to clear the vagina of other sperm in the context of a second (or more) mating, thus giving the later males a larger chance of conception.[citation needed] After mating, the female will wash her vulva thoroughly. If a male attempts to mate with her at this point, the female will attack him. After about 20 to 30 minutes, once the female is finished grooming, the cycle will repeat.[149] Because ovulation is not always triggered by a single mating, females may not be impregnated by the first male with which they mate.[151] Furthermore, cats are superfecund; that is, a female may mate with more than one male when she is in heat, with the result that different kittens in a litter may have different fathers.[149] A newborn kitten The gestation period for cats is between 6467 days, with an average length of 66 days.[152] The size of a litter averages three to five kittens, with the first litter usually smaller than subsequent litters. Kittens are weaned at between six and seven weeks, and cats normally reach sexual maturity at 510 months (females) and to 57 months (males), although this can vary depending on breed.[149] Females can have two to three litters per year, so may produce up to 150 kittens in their breeding span of around ten years.[149] Cats are ready to go to new homes at about 12 weeks old,[153

or when they are ready to leave their mother. Cats can be surgically sterilized (spayed or castrated) as early as 7 weeks to limit unwanted reproduction.[154] This surgery also prevents undesirable sex-related behavior, such as aggression, territory marking (spraying urine) in males and yowling (calling) in females. Traditionally, this surgery was performed at around six to nine months of age, but it is increasingly being performed prior to puberty, at about three to six months.[155] In the USA approximately 80% of household cats are neutered. Throughout many mammal species, males have developed keratinized penile spines along the glans and/or shaft of their penis that may be involved in sexual selection. These spines have been described as being simple, single-pointed structures (macaques) or complex with two or three points per spine (prosimians).[1] Penile spine morphology may be related to mating strategy. Penile spines in chimpanzees and mice are small surface projections made by the piling up of keratinized cell layers in the outermost skin surface.[2][3] In contrast, the common structures found in humans are substantially larger, appear to be an outpocketing of both surface and underlying connective tissue layers, and lack the rich innervation seen in other animals.[4][5] Thus the relationship between the structures is still uncertain.[6] In the primate line from which humans have evolved, a regulatory DNA sequence associated with the formation of small keratinized penile spines was lost. This simplification of penis anatomy may be associated with the monogamous mating habits of humans[7] In species which retain the full expression of penile spines, penile spines contribute to sexual pleasure and quicker orgasms.[8] Hirsuties coronae glandis, found in humans, are sometimes described as vestigial remnants of penile spines.[2] An hCONDEL (highly conserved region of DNA that contains deletions in humans) located near the locus of the androgen receptor gene may be responsible for the loss of penile spines in humans.[9] Felines, especially domestic cats are well-known for having penile spines.