Gestation period
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For mammals the gestation period is the time in which a fetus develops, beginning with fertilization and ending at birth. [1] The duration of this period varies between species.
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[edit] Duration
The gestation period is divided into two major periods: the embryonic period during which time the development of the embryo takes place, and the foetal period that completes the development of the foetus before birth. In humans the embryonic period constitutes 20% of the whole gestation period, and the foetal period 80% of the whole. In mice and rats used in research, the opposite is seen where the embryonic period constitutes 80% of the gestation period and the foetal period 20% in a yet another demonstration of the Pareto principle.
For most species, the amount a fetus grows before birth determines the length of the gestation period. Smaller species normally have a shorter gestation period than larger animals. [2] For example, a cat's gestation normally takes 58–65 days while an elephant's gestation takes 645 days. [3] However, growth does not necessarily determine the length of gestation for all species, especially for those with a breeding season. Species that use a breeding season usually give birth during a specific time of year when food is available.[2]
Various other factors can come into play in determining the duration of gestation. For humans, males normally gestate several days longer than females and multiple pregnancies gestate for a shorter period.[2] Ethnicity may also lengthen or shorten gestation.[4] Some events, such as preterm birth, can greatly shorten the length of gestation.
[edit] Gestation periods
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| Animal | Gestation period (days) |
|---|---|
| Mammals | |
| baboon | 187 |
| bear (black) | 210 |
| bear (grizzly) | 225 |
| bear (polar) | 240 |
| beaver | 122 |
| buffalo (American) | 270 |
| camel (Bactrian) | ~410 |
| cat (domestic) | 58–65 |
| chimpanzee | 230–250 |
| chinchilla | 110–120 |
| chipmunk | 31 |
| cow | 279–292 |
| deer (white-tailed) | 201 |
| dog (domestic) | 58–70 |
| donkey | 365 |
| elephant (Asian) | 645 |
| elk (Wapiti) | 240–250 |
| fox (red) | 52 |
| giraffe | 420–450 |
| goat (domestic) | 145–155 |
| gorilla | 257 |
| guinea pig | 68 |
| hippopotamus | 225–250 |
| horse | 330–342 |
| kangaroo | 42 |
| leopard | 92–95 |
| lion | 108 |
| llama | 330 |
| mink | 40–75 |
| monkey (rhesus) | 164 |
| moose | 240–250 |
| mouse (domestic white) | 19 |
| mouse (meadow) | 21 |
| muskrat | 28–30 |
| opossum (American) | 12–13 |
| otter | 270–300 |
| pig (domestic) | 112–115 |
| porcupine | 112 |
| puma | 90 |
| rabbit (domestic) | 30–35 |
| raccoon | 63 |
| rhinoceros (black) | 450 |
| seal | 330 |
| sea lion (California) | 350 |
| sheep (domestic) | 144–151 |
| squirrel (gray) | 30–40 |
| tiger | 105–113 |
| whale (sperm) | 480–500 |
| wolf | 60–68 |
| wombat | 26–28 |
| zebra (Grant's) | 365 |
| Birds | |
| chicken | 20–22 |
| duck | 26–28 |
| finch | 11–14 |
| goose | 25–28 |
| parrot | 17–31 |
| pheasant | 24 |
| pigeon | 10–18 |
| quail | 21–23 |
| swan | 33–36 |
| turkey | 28 |
[edit] See also
[edit] References
- Gestation, Incubation, and Longevity of Selected Animals
- David Crystal, The Cambridge Factfinder Cambridge: Cambridge University Press, 1998 (84).
[edit] Notes
- ^ "Gestation period". McGraw-Hill's AccessScience Encyclopedia of Science & Technology Online. McGraw-Hill. http://www.accessscience.com/abstract.aspx?id=288400&referURL=http%3a%2f%2fwww.accessscience.com%2fcontent.aspx%3fid%3d288400.
- ^ a b c "gestation". Britannica - The Online Encyclopedia. Encyclopedia Britannica. http://www.britannica.com/EBchecked/topic/232124/gestation.
- ^ "Average Animal Gestation Periods and Incubation Times". MSN Encarta. Microsoft. http://encarta.msn.com/media_701500881/average_animal_gestation_periods_and_incubation_times.html.
- ^ "Does gestation vary by ethnic group? A London-based study of over 122000 pregnancies with spontaneous onset of labour". International Journal of Epidemiology. http://ije.oxfordjournals.org/cgi/content/full/33/1/107.
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