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hand (and intimacy) of hominids

How is that ancestral hominids living is something that would give us valuable information about how to We are who we are and, fortunately, is a topic of interest to a handful of scientists who at this time questions are asked what were the social life and relationships of our ancestors? Were monogamous or polygamous? bones and debris left behind tell us much less than we would like to know about your social life. And the more information-and more species of hominid, are appearing in the picture more doubts arise about their social life. Because we only have this information, it becomes necessary to take full advantage. Fortunately, the fossil-even when fragmented and limited, can give interesting information. Its size, for example, is possible to deduce several things. The sexual dimorphism, ie the size difference observed between males and females of a species is a feature that has been used to predict social behavior. The larger males over females, the greater the competition between males for access to females. Other features may also be associated with such competition as is the size of the canine . Using the degree of sexual dimorphism to infer the social life of extinct hominids becomes more difficult because, among other things, to other characteristics of the group for which there is currently debate, for example, the size of the canines. And in cases like this when, to turn over certain methodological problems emerge ideas such as using other indicators of the social life of the species, such as those related to sexual selection . This is the proposal of a study by Emma Nelson , Rolian Campbell, Lisa Cashmore and and Susanne Shultz The results were published just recently in the journal Proceedings of the Royal Society . The multinational and multidisciplinary group for study considered the ratio between the second (index finger) and the fourth digit (ring finger), ie the result of dividing the length of the index finger between the length of the ring. The proportion to which commonly referred to as 2D: 4D , is considered a marker of prenatal sex hormones.

have seen that the proportion 2D: 4D is sexually dimorphic in humans, being generally lower in men than in women. Additionally, we have seen that a low proportion 2D: 4D is associated with dominance-related behaviors in both sexes. Even at the population level has been linked with polygynous systems. This relationship is also maintained in nonhuman primates and has been shown that the proportion is higher in monogamous species than in those more promiscuous and characterized by competition between males.

Hand with shorter index than ring fingers (a low ratio between the second and fourth fingers) which indicates high exposure to testosterone in the womb. Image taken from Wikipedia .

Therefore, to investigate the social system of extinct hominids that we had enough information on their hands, and since only we have the bones of the hands of several of Emma and her team used the size of the phalanges. For their study, then, the proportion used 2D: 4D ratio unless 2FP: 4FP, where FP refers to the proximal phalanx . Emma and colleagues used fossils housed in museum collections, as well as information reported in other articles on existing hominids, ie Homo sapiens , and extinct as Pierolapithecus catalaunicus , Hispanopithecus laietanus (an ancestral ape), Ardipithecus (the recently discovered "Ardi"), Australopithecus afarensis (like the famous Lucy), and Homo neanderthalensis (our closest relative in the sample). used for their comparisons contemporary measures monogamous apes such as gibbons (Hylobates ) and promiscuous apes such as chimpanzees, orangutans and gorillas (Pan , Pongo and Gorilla , respectively). In such a way that counting the dimensions of the phalanges of extinct hominids and man, as well as measures of the phalanges and information about the social life of contemporary apes and man, it was possible to infer the behavior of extinct hominids. It is important to note that in case of Homo sapiens social system was considered as an intermediate between monogamy and polygyny. Ardi The results indicate that the ancestral apes, Neanderthals and humans would all devotees of polygyny, but a system would be characterized monogamous australopithecenes , ie Lucy and her relatives. However, the variability in the proportions of our closest relatives digital Homo neanderthalensis suggests that these hominids of the Pleistocene, as well as contemporary humans, they could have shown some flexibility in their social system and mating habits, ie could been found between monogamy undecided and promiscuity. These results suggest beyond as they might have been the headlines of the Pleistocene version of the journal Hello! , also suggests that the transition from a polygynous one (potential or mostly) monogamous may have occurred late in human evolutionary history. The earlier proposal, placed on the table by other authors, I would agree with theories that suggest that a monogamous system would have evolved hand in hand with the increase in brain size evolution genus Homo. Not that being monogamous is (necessarily) mean being smart in the animal world, but because big brains are expensive and monogamy may be the ideal social system to pay its price. Let's see why.

The big brains of human babies, compared to other species, requires a considerable amount of parental care for an extended period of time and the fact that, despite this, the human species is highly fecund in hominids is attracting attention. The species with large brains in relation to body size are generally little productive. However, the exception to this rule are those species in which there is a dedicated parental care.

Breeding Homo sapiens. Stock Bùi Linh Ngan taken Wikimedia Commons.

In the human case, in particular, high fertility may in some cases maintained only if it has the support of both parents, especially if we think human in such demanding situations such as a hunter-gatherer and / or a nomad. The fact that, considering the proportion 2FP: 4FP, humans are at an intermediate point between monogamy and polygyny also suggests that pairing in this species differs from other monogamous primates. We can say that, biologically speaking, the human system is rather one in which both females and males tend to have multiple partners, but exhibit a tendency to monogamy when it comes to raising their offspring. Judging by the proportion of the bones of the hand, the social systems of the Neanderthals and modern humans would be similar and characterized by some degree of competition in the acquisition of partners. This is consistent with the idea that both members of the genus Homo showed similarities in their development. As we see, the hands-and in particular the bones of the fingers can tell us about the social life of the species, including extinct hominids. The more you appear older fossils may be the scope of studies like Emma and their collaborators. There are still many mysteries to be solved than when the hominid brain became so great that shared parenting was a prerequisite for the survival of offspring? What other factors in the history of our ancestors spoke to was a transition from polygyny to a system closer to monogamy? What ways-if any-are linked the evolution of brain size, parental care and sexual dimorphism? Sure there are currently few others paleobiologist wondering what lay hands tools to answer these and other electrifying unknowns. Reference article:

Nelson, E., Rolian, C., Cashmore, L., & Shultz, S. (2010). Digit ratios predict polygyny in early apes, Ardipithecus, Neanderthals and Early Modern Humans But Not in Australopithecus Proceedings of the Royal Society B: Biological Sciences DOI: 10.1098/rspb.2010.1740
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-------------------- Please read the article by Dan Jones " A window on the past " published on April 25, 2009 in the journal New Scientist .