Sandman has a post up, Can There Be A Synthesis Between Cultural And Biological Evolution?, taking off on the PLoS Biology article, Across the Curious Parallel of Language and Species Evolution. Read both. I would add one important point though: linguistic and biological evolution are simply subsets of evolutionary dynamics. That is why Martin Nowak’s book of that name, Evolutionary Dynamics, naturally has a section on the evolution of language. Several evolutionarily oriented thinkers have attempted to translate models originally developed for biology into the domain of culture. Cultural Transmission and Evolution and Culture and the Evolutionary Process are two works which I think are good introductions to the field.
I think it is important to emphasize that various evolutionary genetic parameters such as selection, drift and migration are operative in cultural evolution. This means that the evolutionary dynamics of language extend beyond the debate as to the relevance of functionalism to anthropology, just as evolution on the molecular level is more than simply adaptation. Additionally, the adaptation of cultural traits must be measured as both intrinsic and extrinsic to the mind. That is, particular cultural adaptations may be evaluated against their fitness implications against the environment (e.g., the extent of clothing) or social milieu (e.g., structures which mediate rank order and enable group cohesion to operate smoothly). But others are almost certainly canalized by the constraints and incentives which are inherent within the structural parameters of the human mind. Any given cultural trait may span all these dimensions, or limit itself to one dimension. For example, it seems rather clear that religious ideas are strongly constrained/adapted to the nature of the human mind. On the other hand, the question as to whether religious ideas are constrained/adapted exogenously to the mind is an open question, they may well be, or they may not.
Then there is the matter of substrate. Biological evolution is gifted with a discrete and concrete unit of replication, the physical gene. The structure of the gene and the process of meiosis result in the emergence of endogenous parameters which have an affect on biological evolution; e.g., the parameter of recombination which is conditioned by the physical nature of DNA. In contrast, cultural evolution has no atomic unit to which we can ascribe bookkeeping functions. Cultural evolution may be considered to operate by principles of blending of traits, but this misses some important nuances.
For example, the transmission process in cultural evolution is extremely malleable and exhibits far less invariance and regularity than that of biological evolution mediated by genes. A child may adopt the values of one parent to the total exclusion of others. Except in the case of mitochondria one can generally state that the offspring receives half of its genetic material from each parent in the case of diploid sexually reproducing organisms. Many social insects are characterized haplodiploidy. Asexual organisms reproduce in a clonal manner. And so forth. The set of various modes of transmission is finite and not so numerous as to be intractable (ergo, the reasonableness of a few categories such as haploid, diploid, haplodiploid, sexual, asexual, hermaphroditic, etc.).
Cultural transmission is a much more statistical affair. Though one can posit models of total transmission of cultural values via one parent (e.g., Judaism transmitted through the mother), these are often exceptional cases, and generally the rate of deviation from the norm is high. Blending inheritance in evolutionary biology was always problematic because of the rapid diminishing of variation, but in cultural process this is not an issue. Additionally, the nature of variation across populations differs a great deal in culture from that of genetics. Genetic variation usually exhibits a clinal pattern so that demes only change gradually in character; this is due to the power of gene flow in eliminating between group variance. This is one reason that many evolutionary biologists are skeptical of the power of higher than individual level selection, within group genetic variation is usually much greater than between group variance, and the power of selection is directly proportional to the extent of said variance.
No so for culture. Going back to language, consider the rapid changes in dialect that can occur across group boundaries. Because it seems plausible that we have a “language organ” the trait is atypical in some ways, but it still exhibits differences from biological variation that illustrate the general pattern. In small tribes one can posit that there is almost no within group variance in accent. If an individual from the outside marries into the group their offspring will carry half their genes, but, it is likely that very little of their cultural traits will be passed down because of the strong incentives for the children of a foreigner to adhere closely to the norms of their tribe. While genetic variation can be thought of as the gentle rolling sweeps of hills gradually rising and fall across the landscape, cultural variation many manifest as a set of sharply demarcated plateaus and ravines cutting a very rugged and fragmented landscape. This of course is a better context for higher-than-individual level selection to occur!
Finally, there is the issue of biology-culture evolution. This is perhaps the most important point of synthesis and cross-fertilization between these two domains of evolutionary dynamics. Lactase persistence for example is probably the classic case. But there are others, such as the CNV work on amylase, or the affect of Toxoplasma gondii on the central tendency of various societies in regards to personality. Exciting times….