古代人類祖先（人科動(dòng)物）可能在人屬進(jìn)化出來之前就已經(jīng)生出了較大的嬰兒,，并發(fā)展出了高強(qiáng)度,、合作進(jìn)行的新生兒護(hù)理方式——這是把人類和大猿區(qū)別開來的特征,。Jeremy DeSilva使用來自一個(gè)全國(guó)靈長(zhǎng)類研究中心,、博物館樣本和此前研究的信息,，來檢驗(yàn)一個(gè)常見的主張：即比例來算,，人類嬰兒比猿的嬰兒更重，同時(shí)也試圖確定在人類進(jìn)化過程中這種朝著更大的嬰兒進(jìn)化的轉(zhuǎn)變發(fā)生在什么時(shí)候,。DeSilva發(fā)現(xiàn)人類嬰兒大約是母親體重的6%,，而黑猩猩的新生兒體重接近母親體重的3%。由于更大的新生兒更難分娩而且更重而難以攜帶,，一些科研人員已經(jīng)提出，人類的撫養(yǎng)子女的特征——諸如父親和家族其他成員參與新生兒護(hù)理——可能與猿人開始直立行走同時(shí)出現(xiàn),。然而,，DeSilva提出，盡管最早的人科動(dòng)物顯示出了類似于今天的猿的新生兒-母親體重比例,，南方古猿屬（一種如今已經(jīng)滅絕的人科動(dòng)物群,，在大約400萬年前進(jìn)化出來）的雌性可能生出超過其體重5%的嬰兒。DeSilva說,，該研究提示,，人類進(jìn)化史中父母共同撫養(yǎng)子女的開始可能比此前科研人員認(rèn)為的更早。（生物谷Bioon.com）
生物谷推薦原文出處：
PNAS doi: 10.1073/pnas.1003865108
A shift toward birthing relatively large infants early in human evolution
Jeremy M. DeSilva
Abstract
It has long been argued that modern human mothers give birth to proportionately larger babies than apes do. Data presented here from human and chimpanzee infant:mother dyads confirm this assertion: humans give birth to infants approximately 6% of their body mass, compared with approximately 3% for chimpanzees, even though the female body weights of the two species are moderately convergent. Carrying a relatively large infant both pre- and postnatally has important ramifications for birthing strategies, social systems, energetics, and locomotion. However, it is not clear when the shift to birthing large infants occurred over the course of human evolution. Here, known and often conserved relationships between adult brain mass, neonatal brain mass, and neonatal body mass in anthropoids are used to estimate birthweights of extinct hominid taxa. These estimates are resampled with direct measurements of fossil postcrania from female hominids, and also compared with estimates of female body mass to assess when human-like infant:mother mass ratios (IMMRs) evolved. The results of this study suggest that 4.4-Myr-old Ardipithecus possessed IMMRs similar to those found in African apes, indicating that a low IMMR is the primitive condition in hominids. Australopithecus females, in contrast, had significantly heavier infants compared with dimensions of the femoral head (n = 7) and ankle (n = 7) than what is found in chimpanzees, and are estimated to have birthed neonates more than 5% of their body mass. Carrying such proportionately large infants may have limited arboreality in Australopithecus females and may have selected for alloparenting behavior earlier in human evolution than previously thought.
