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发帖数: 2273 | 1 Genes Play Major Role in Primate Social Behavior, Study Finds
By NICHOLAS WADE
Social behavior among primates — including humans — has a substantial
genetic basis, a team of scientists has concluded from a new survey of
social structure across the primate family tree.
The scientists, at the University of Oxford in England, looked at the
evolutionary family tree of 217 primate species whose social organization is
known. Their findings, published in the journal Nature, challenge some of
the leading theories of social behavior, including:
¶ That social structure is shaped by environment — for instance, a
species whose food is widely dispersed may need to live in large groups.
¶ That complex societies evolve step by step from simple ones.
¶ And the so-called social brain hypothesis: that intelligence and
brain volume increase with group size because individuals must manage more
social relationships.
By contrast, the new survey emphasizes the major role of genetics in shaping
sociality. Being rooted in genetics, social structure is hard to change,
and a species has to operate with whatever social structure it inherits.
If social behavior were mostly shaped by ecology, then related species
living in different environments should display a variety of social
structures. But the Oxford biologists — Susanne Shultz, Christopher Opie
and Quentin Atkinson — found the opposite was true: Primate species tended
to have the same social structure as their close relatives, regardless of
how and where they live.
The Old World monkeys, for example, a group that includes baboons and
macaques, live in many habitats, from savanna to rain forest to alpine
regions, and may feed on fruit or leaves or grass. Yet all have very similar
social systems, suggesting that their common ancestry — and the inherited
genes that shape behavior — are a stronger influence than ecology on their
social structure.
“We were trying to test accepted models of social evolution and have shown
that in primates it happens via a different pathway than we always assumed,
” Dr. Shultz said.
The researchers suggest that sociality emerged about 52 million years ago.
The earliest primates sought safety by being solitary and inconspicuous,
moving only at night. It seems that when they shifted to daytime activity,
they sought safety in numbers.
It was from these loose, unstructured groups that more specific forms of
primate social behavior began to evolve, some 16 million years ago. These
included pair bonding, an arrangement adopted by gorillas and humans, and
the multi-male, multi-female groups typical of baboons and chimpanzees.
The fact that related species have similar social structures, presumably
because the genes for social behavior are inherited from a common ancestor,
“spells trouble” for ecological explanations, Joan B. Silk, a primate
expert at the University of California, Los Angeles, wrote in a commentary
in Nature. Also, the finding that there has not been a steady progression
from small groups to large ones challenges the social brain hypothesis, Dr.
Silk said.
The Oxford survey confirms that the structure of human society, too, is
likely to have a genetic basis, since humans are in the primate family, said
Bernard Chapais, an expert on human social evolution at the University of
Montreal.
“Evolutionary change in any particular lineage is highly constrained by the
lineage’s phylogenetic history,” Dr. Chapais said, referring to the
evolutionary family tree. “This reasoning applies to all species, including
ours. But in humans, cultural variation hides both the social unity of
humankind and its biological foundation.”
Human multifamily groups may have arisen from the gorilla-type harem
structure, with many harems merging together, or from stable breeding bonds
replacing sexual promiscuity in a chimpanzee-type society, Dr. Chapais said.
In his book “Primeval Kinship” (Harvard, 2008), he describes a further
stage in human social evolution that occurred when individual bands allied
with those with whom they exchanged daughters. The bands in such a marital
exchange system formed a tribe, taking human society to a level of
organization beyond that of chimpanzee society.
With chimps, territorially based bands also exchange daughters to avoid
incest but continue to fight with one another to the death because the males
cannot recognize their kinship with relatives in neighboring bands. |
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