DIFFERENT PERSPECTIVES OF LANGUAGE EVOLUTION
Even though there is certainly no consensus yet，not even about what an adequate theory of language evolution should look like，there is at least a widespread agreement about the origins and evolution of language that is based on a congruence of three different evolutionary processes，influencing and reinforcing each other：biological evolution，socio-ecological evolution，and cultural evolution.
From the perspective of biological evolution，language is regarded as a species.Darwin wrote：“The formation of different languages and of distinct species...［is］curiously parallel...We find in distinct languages striking homologies due to community of descent，and analogies due to a similar process of formation”（Darwin 1871：465-466）.Of course，this stand leads to some objections.1For example，one objection comes from Premack D.（1985），who argued that：“Human language is an embarrassment for evolutionary theory because it is vastly more powerful than one can account for in terms of selective fitness.A semantic language with simple mapping rules，of a kind one might suppose that the chimpanzee would have，appears to confer all the advantages one normally associates with discussions of mastodon hunting or the like...syntactic classes，structure-dependent rules，recursion and the rest，are overly powerful devices，absurdly so”.And besides Premack's insightful opinion on language evolution，we aslo put some doubt on this stand that the oversimplification of language evolution process fails to figure out how environmental variables force language change，and by what？
Nevertheless，Evolutionary biology has been widely invoked to account for human behavior，language，and social institutions.These explanations have generated sociobiology（Trivers 1985；Wilson 1975），human behavioral ecology（Borgerhoff Mulder 1991），and evolutionary psychology（Barkow et al.1992），as well as evolutionism and social Darwinism（Kuper 1988）.In fact，the complexity of language evolution just reflects the complexity of human species physical，biological and social networks.
Biologically，there is a complex interplay between language evolution and brain evolution.Language must，by definition，be learnable by the brains of children in each generation（Schoenemann，2009：163）.This let us to ask such a question：“Does language change start from acquisition process？”Probablly，language acquisition may be seen as a reflexive activity.The interaction in dyads is multimodal：voice，rhythm and facial expressions interact to create mutual understanding and agreement on steps to take.In this way，we can say language and brain get coevolved as the result of a complex adaptive system.For example，recent findings of nervous systems evolutions are likely relevant to language evolution（Gary Cziko 1997），which include becoming more centralized and hierarchical in architecture，a trend toward concentration of neurons and sense organs，a larger brain size，and an increase in plasticity.
In recent years，on the other hand，natural scientists have considered the possibility that the emergence of human cultural evolution has distinct and novel characteristics that are not simply reducible to biological or genetic factors.The findings published in Nature by Michael Dunn et al（2011）have proved that the evolution of only a few word-order features of languages are strongly correlated，which is contrary to the generative account of parameter setting in our brain.In addition，contrary to the Greenbergian generalizations，they show that most observed functional dependencies between traits are lineage-specific rather than universal tendencies.These findings support the view that—at least with respect to word order—cultural evolution is the primary factor that determines linguistic structure，with the current state of a linguistic system shaping and constraining future states.
In other words，culture amplifies the capacity of human beings to modify sources of natural selection in their environments to the point where that capacity raises some new questions about the processes of human adaptation.From this pointview，we argue evolutionary processes take place at two linked levels：replication and selection.Replicators are replicated，but with cumulating errors resultant from mutation and recombination and in these ways variation is generated.Selection is a process by which interactors in interaction with their environment cause replication to be differential.
Language evolution definitly is being involved with social and demographic factors.Kevin N.Laland et al（2000）claims that Social and demographic factors affect rates of language change within populations of speakers，include social status，the strength of social ties，the size of the population，and levels of outside contact.These forces may influence rates of evolution on a local and temporally specific scale.For example，when language is divided into small groups，the changes will occur.The diversity of languages is used“to maintain social groupings at a small and manageable level—and，conversely，to keep other groups at a distance”（Laycock1982：35）.
As we can see the three evolutions above are the sources for explaining language evolution processes.Socio-ecological evolution is our best source for explaining the reasons why humans speak.The ecological pressures at the dawn of our species must have encouraged symbolic communication and the complexity of social structures must have grown to cope with these pressures.Biological evolution is our best source for explaining how the embodiment and neural architecture necessary for language have originated and how they get reconstructed in development.And cultural evolution is our best source for explaining how specific language subsystems，for example a tense-aspect system，may emerge and culturally propagate in a population.The three evolutions are the forces shaping the emergence of language complexity（see Figure 1）.Increasing the linguistic complexity will increase the brain capacity，and follow the increased social and ecological complexity.So this is a circle working together to force language change.
Figure 1 Three forces shaping the emergence of language complexity in a spiraling process（Luc Steels 2011）
If language is a complex adaptive system，here we may say，language evolution is realized by biological，Socio-ecological and cultural evolution processes.And organism and environments work together，interacting each other and adapting each other.Such ecological interactions are evolutionarily conserved across the entire tree of life.During the ecological interacting，organisms may cooperate selectively with reciprocators and benefit from social information.And these social organisms may enforce cooperation through rewards and punishment to secure effective communication which enhances the social function of language behavior.In turn，social interactions may affect individual learning and biological fitness.Here we must emphasize a very important concept“selve”，which is the agent of language evolution.As Giddens（1999）points out，in each social encounter we adjust ourselves and our linguistic and non-linguistic behavior to suit the demands of that social situation，which implies that an individual has as many“selves”as there are divergent contexts of interaction.
So far，we talk about so many static and basic factors involved with language evolution.They are the macro-level of language evolution，which shaping the emergence of language complexity.Nevertheless，we never ask ourselves what about the role of each individual self in the play of such evolution，what about our body，senses，and brain，even the tiny neurons in our nervous system influencing us when we are acquiring language，learning language and communicating with others.The significant but ignored micro-level factors must be considered when language evolution is under the way；after all，we human beings are the agent to interact with each other and the environment.We are the bridges between the internal and the external causal features.Therefore，next we will go back to the very fundamental part of language communication to probe some significant factors at the micro-level that influence language evolution.