Erbgut des Gorillas entschlüsselt: Wie nahe sind wir verwandt?

Ein Bericht im Spiegel zur Entschlüsselung des Erbguts von Gorillas:

Die Genom-Analyse bestätigte zudem, dass der Schimpanse und nicht der Gorilla der nächste Verwandte des Menschen ist. Das Erbgut enthüllte aber auch Unerwartetes: 15 Prozent des menschlichen Genoms sind dem des Gorillas ähnlicher als dem des näher verwandten Schimpansen. Umgekehrt teilen Schimpansen 15 Prozent ihrer Gene nur mit dem Gorilla – obwohl sie mit ihm weniger nahe verwandt sind als mit dem Menschen.

„Wir haben herausgefunden, dass Gorillas viele genetische Veränderungen mit dem Menschen gemein haben, darunter die Entwicklung des Gehörs“, sagte Mitautor Chris Tyler-Smith vom Sanger Institute. Bisher hatte man angenommen, dass die rasche Entwicklung des menschlichen Gehörs im Zusammenhang mit der Sprachentwicklung steht. Beim Gorilla hat sich das Gehör dem Genomvergleich zufolge jedoch ähnlich schnell entwickelt.

Alle drei – Mensch, Schimpanse und Gorilla – teilen zudem rund 500 Gene, die sich besonders schnell im Laufe der Evolution verändert haben. „Diese Gene sind mit Funktionen wie der Sinneswahrnehmung, dem Gehör und der Gehirnentwicklung verknüpft“, berichten die Forscher.

Das finde ich sehr interessant. Zum einen stützt es Theorien von David Geary, die er in „Male / Female“ darlegt. Dieser meint, dass unsere Vorfahren unter ähnlichen Verhältnissen wie die Gorillas gelebt haben, mit starker intrasexueller Konkurrenz unter Männchen. Es zeigt auch unsere sonstige Gemeinsamkeit mit den Menschenaffen

David Geary zu den Ähnlichkeiten mit Gorillas (PDF):

For reasons described next, we suggest that certain features of the social behavior of australopithecines may have been more similar to that seen in modern gorillas than in chimpanzees or bonobos. We are not arguing that australopithecines were gorilla-like in every sense, as they clearly were not (e.g., they were bipedal). Rather we believe that a gorilla-like model for australopithecine social dynamics provides an evolutionary launching point that more readily accommodates certain patterns of human parental behavior, such as male parenting, and family formation than does either a chimpanzee-like or bonobo-like social structure. At the same time, there are also similarities between human and chimpanzee behavior, especially male coalitions, and thus arguments can be made that australopithecines also evidenced this form of social competition. This is, of course, a possibility that cannot be ruled out. We are suggesting that an alternative be considered: Male coalitional behavior may have evolved independently in humans and chimpanzees and may not have been an important feature of the reproductive strategy of male australopithecines.

Male – male competition, social structure, and brain size. The degree of sexual dimorphism in A. anamensis and A. afarensis suggests intense one-onone male – male competition and perhaps a gorilla-like social structure (Leakey et al., 1998). Although other social structures are, of course, possible (Plavcan, 2000), a gorilla-like social structure is consistent with many features of human social organization. The modal social organization of both lowland gorillas (Gorilla gorilla gorilla) and mountain gorillas (Gorilla gorilla beringei) is single-male harems, which typically include one reproductive male, many females, and their offspring (Fossey, 1984; Stewart & Harcourt, 1987; A. B. Taylor, 1997). In lowland gorillas, several of these families may occupy the same geographical region and are often in proximity, whereas in mountain gorillas they are geographically isolated. In both cases, adult male and female gorillas often form long-term social relationships, and male gorillas, presumably due to high levels of paternity certainty associated with single-male harems, show high levels of affiliation with their offspring. “Associated males hold, cuddle, nuzzle, examine, and groom infants, and infants turn to these males in times of distress” (Whitten, 1987, p. 346). The reduction in the magnitude of the sexual dimorphism, combined with coalitional aggression in extant human populations (e.g., Chagnon, 1988; Keeley, 1996), is consistent with the emergence of coalition-based male – male competition during hominid evolution, perhaps with the emergence of H. erectus. Still, coalitional behavior is more typical among female primates than among male primates. In these species, females are the philopatric sex — that is, the sex that stays in the birth group (Wrangham, 1980). Female-biased philopatry results in a degree of genetic relatedness among females that supports coalition formation when such behavior covaries with survival or reproductive outcomes (Sterck, Watts, & van Schaik, 1997). For human beings, chimpanzees, bonobos, and gorillas (sometimes sons inherit the harem), philopatry is male biased, not female biased, suggesting that the male-biased philopatry has a long evolutionary history in African hominoids (Ghiglieri, 1987; Pasternak et al., 1997; Stewart & Harcourt, 1987). Male-biased philopatry is important because it creates social conditions that can lead to the evolution of male kin-based coalitions (Foley & Lee, 1989). Unlike female coalitions, male coalitions are focused on competition for mates rather than competition for food (Wrangham, 1999). As described for chimpanzees, a coalition of male hominids would have had a competitive advantage over a lone male, even a larger male.

(…)

Paternal investment, concealed ovulation, and female – female competition. If the social structure of A. anamensis and A. afarensis was similar to that found in gorillas, then it would be possible that there are continuities in male parenting, male – female relationships, and family structure between these australopithecines and human beings. In fact, if the social structure of these australopithecines were similar to that found in gorillas, then the evolutionary emergence of human families would be straightforward. Once lone males were replaced by kin-based multimale coalitions, the males and females of these species would likely maintain the preexisting social deep structure — a basic social organization that included one adult male, one or a few adult females, and their offspring, as well as long-term male – female relationships and male parenting (Lovejoy, 1981; Stewart & Harcourt, 1987). The primary difference is that these families would be nested within the larger community rather than being geographically (mountain gorillas) or socially (lowland gorillas) separated. As noted, lowland gorilla families are often in proximity, but they are not socially bonded together through a kin-based coalition or social network. In other words, human families are similar in many respects to gorilla families, with the addition that in most preindustrial societies human families are nested within a larger male kin-based community (Pasternak et al., 1997). The emergence of male kin-based coalitions and thus multimale, multifemale communities with many reproductive males (see Table 1) would have resulted in an exponential increase in the complexity of social relationships relative to that evident in gorillas. In particular, this change in social structure increases the mating opportunities of both males and females, increases the risks of cuckoldry, and thus creates a social ecology that could potentially result in the evolution of reproductive dynamics similar to that found in other mammals — a male focus on mating and a female focus on parenting (Clutton-Brock, 1989). The issue is the mechanisms responsible for the maintenance of a family-focused social organization rather than the eventual evolution of the standard mammalian pattern.

Der verlinkte Text ist 63 Seiten lang, ich rege dazu an, es sich durchzulesen.

Ob der Mensch dabei etwas mehr mit dem Schimpansen oder mit dem Gorilla gemein hat erscheint mir dabei nebensächlich. Denn die Linien trennten sich eben irgendwann und der Mensch hat sich verändert. Die zeitliche „Einbettung“ zwischen Gorilla und Schimpansen, die beide eine starke intrasexuelle Konkurrenz zeigen, macht aber deutlich, dass auch unsere Linie eine solche Konkurrenz einmal kannte. Meiner Meinung nach spricht viel im menschlichen Verhalten dafür, dass davon auch noch etwas übrig geblieben ist.