As a result, this behavior is by no means rare in the animal kingdom: Lions and horses, for instance, are also known for killing the offspring of females they want to mate with.
Alberts and her colleagues traced a roughly 6 percent spike in feticide two weeks after a new male immigrated to a group. They also studied the data for evidence of infanticide and found similar patterns. Deaths of infant baboons increased by little over 2 percent two weeks after a male baboon immigrated to the group.
For decades Cheney has documented infanticide in baboons in Botswana, where the behavior accounts for at least 50 percent of all infant deaths. Cheney notes that, in the Botswana populations at least, a dominant male typically mates with multiple females—in the process fathering a high proportion of infants—but only retains his tenure as alpha male for a few months.
Other factors include group size and access to available females. So what can these findings tell us about the workings of human society? In this case, the principle is that males and females may have conflicts of interest with respect to reproduction.
Infants weigh about 2 lbs. They only drink their mother's milk until they start weaning at 3 to 4 months old. Like with human infants, weaning can be a long process full of tantrums. A little before a baboon turns 2 years old, it starts becoming a juvenile and grows one pound every three months, according to the Amboseli Baboon Research Project. They become mature at around 6 to 8 years old.
Males typically leave their troops when they become adults while the females stay. Males will often join other troops and leave again many times throughout their lives. Baboons can live up to 30 years in the wild. Female baboons can reproduce even when they get very old, unlike human females. Here is the taxonomy of baboons, according to Integrated Taxonomic Information System :. Also, Gelada baboons are members of the Papionini tribe, but are in a different genus.
Their scientific name is Theropithecus gelada. The baboon's primary predators are humans, cheetahs and leopards. All of them are listed as least concern, except for one. The Guinea baboon is listed as near threatened because it is believed that they may have lost 20 to 25 percent of their home range in the past 30 years.
This range loss is due greatly to human farming and hunting. Baboons can talk, sort of. Baboons at Gombe have been observed since , with continuous demographic data collected since Data were collected on two distinct study groups, which subsequently split several times throughout the years, yielding a total of 9 troops with a mean size of These data include daily reproductive status of females, immigration and emigration events, births, and deaths.
Male and female ranks were determined using the outcomes of pairwise interactions between same-sex individuals, with those exhibiting more submissive behaviors in repeated encounters ranked below the individual to which they were submissive.
Birth and miscarriage data are available from to Pregnancy in females is identified by the appearance of bright red coloration on the paracollosal skin of the rump This color change is overt, appearing approximately 3 weeks after the sexual swelling begins to detumesce 25 , and persists until several days after parturition, providing a reliable indicator of reproductive status Gestation typically lasts days Vaginal bleeding by pregnant females and the complete loss of pregnancy coloration were used to estimate fetal age at miscarriage.
The underlying miscarriage rate for Gombe baboons is A significant decrease in rainfall at Gombe over several decades introduced an increasing environmental stressor to females—drought has been shown to increase rates of miscarriage in yellow baboons 23 and rain-mediated food abundance also impacts seasonal reproduction in geladas 35 —and so both 2-year rainfall means and maternal rank were included as predictors in these regressions.
Other predictors, such as group size and maternal age were evaluated in a previous analysis Though age remained the only other significant predictor of miscarriage, its inclusion did not change the 3-way interaction result and thus was not included in the final Cox regression analysis. No distinction was made between infants exposed to one male and those exposed to multiple males; the earliest exposure age was used. Maternal rank and 2-year rainfall means were also used as a predictor in these regressions.
A total of male immigrants with known rank were used in these analyses, with 30 males ascending to top rank within a year of immigration. Though varying in severity, we treated all wounds identically. Fetal age at each wounding event was determined for all pregnancies; unwounded females were classified as having 0 wounds during pregnancy and this score was updated to 1 at the fetal age of the wounding event.
A Cox regression with a time-dependent covariate was then used to calculate the hazard of miscarriage before day for wounded vs. A chi-square analysis was also used to determine whether a disproportionate number of pregnant females were wounded immediately after the arrival of a rapid-rising male as compared to expected. Out of pregnancies, 77 were exposed to males that attained top rank within a year.
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