One of the theory's central claims is that culture evolves partly through a Darwinian selection process, which dual inheritance theorists often describe by analogy to genetic evolution.
DIT recognizes that the natural selection of genotypes is an important component of the evolution of human behavior and that cultural traits can be constrained by genetic imperatives.
DIT makes three main claims:[5] The human capacity to store and transmit culture arose from genetically evolved psychological mechanisms.
For example, the cultural adoptions of agriculture and dairying have, in humans, caused genetic selection for the traits to digest starch and lactose, respectively.
Dual inheritance theorists hypothesize that the demographic transition may be a result of a prestige bias, where individuals that forgo reproduction to gain more influence in industrial societies are more likely to be chosen as cultural models.
Lactase persistence One of the best known examples is the prevalence of the genotype for adult lactose absorption in human populations, such as Northern Europeans and some African societies, with a long history of raising cattle for milk.
Until around 7,500 years ago,[21] lactase production stopped shortly after weaning,[22] and in societies which did not develop dairying, such as East Asians and Amerindians, this is still true today.
[25] This implies that the cultural practice of raising cattle first for meat and later for milk led to selection for genetic traits for lactose digestion.
[34][38] This increased energy intake, more free time and savings made on tissue used in the digestive system allowed for the selection of genes for larger brain size.
[39] With approximately 86 billion neurons in the human brain and 60–70 kg body mass, an exclusively raw diet close to that of what extant primates have would be not viable as, when modelled, it is argued that it would require an infeasible level of more than nine hours of feeding every day.
[40][43] Wrangham argues that anatomical evidence around the time of the origin of Homo erectus (1.8 million years ago), indicates that the control of fire and hence cooking occurred.
[34] At this time, the largest reductions in tooth size in the entirety of human evolution occurred, indicating that softer foods became prevalent in the diet.
Random variation arises from errors in the learning, display or recall of cultural information, and is roughly analogous to the process of mutation in genetic evolution.
[50] A model by Hahn and Bentley shows that cultural drift gives a reasonably good approximation to changes in the popularity of American baby names.
[62] Boyd and Richerson argue that the evolution of cumulative culture depends on observational learning and is uncommon in other species because it is ineffective when it is rare in a population.
[61] Michael Tomasello argues that cumulative cultural evolution results from a ratchet effect that began when humans developed the cognitive architecture to understand others as mental agents.
[66] Based on an earlier model by Cavalli-Sforza and Feldman,[67] Boyd and Richerson show that conformist biases are almost inevitable when traits spread through social learning,[68] implying that group selection is common in cultural evolution.
[70] In 1876, Friedrich Engels wrote a manuscript titled The Part Played by Labour in the Transition from Ape to Man, accredited as a founding document of DIT;[71] “The approach to gene-culture coevolution first developed by Engels and developed later on by anthropologists…” is described by Stephen Jay Gould as “…the best nineteenth-century case for gene-culture coevolution.”[72] The idea that human cultures undergo a similar evolutionary process as genetic evolution also goes back to Darwin.
[47] Borrowing heavily from population genetics and epidemiology, this book built a mathematical theory concerning the spread of cultural traits.
In a 2006 interview Harvard biologist E. O. Wilson expressed disappointment at the little attention afforded to DIT: "...for some reason I haven't fully fathomed, this most promising frontier of scientific research has attracted very few people and very little effort.
"[81]Kevin Laland and Gillian Ruth Brown attribute this lack of attention to DIT's heavy reliance on formal modeling.
"In many ways the most complex and potentially rewarding of all approaches, [DIT], with its multiple processes and cerebral onslaught of sigmas and deltas, may appear too abstract to all but the most enthusiastic reader.
[83] These behavioral economic techniques have been adapted to test predictions of cultural evolutionary models in laboratory settings[84][85][86] as well as studying differences in cooperation in fifteen small-scale societies in the field.
Although findings from traditional ethnologic studies have been used to buttress DIT arguments,[47][55] thus far there have been little ethnographic fieldwork designed to explicitly test these hypotheses.
However, Dual Inheritance theorists charge that both disciplines too often treat culture as a static superorganic entity that dictates human behavior.
[94][95] It is useful for some applications to note, however, that there are ways to pass ideas which are more resilient and involve substantially less mutation, such as by mass distribution of printed media.
[98] Memetics, which comes from the meme idea described in Dawkins's The Selfish Gene, is similar to DIT in that it treats culture as an evolutionary process that is distinct from genetic transmission.
[17] One difference is that memetics' focus is on the selection potential of discrete replicators (memes), where DIT allows for transmission of both non-replicators and non-discrete cultural variants.
[100][101][102] She argues that traits that are not transmitted by way of a self-assembly code (as in genetic evolution) is misleading, because this second use does not capture the algorithmic structure that makes an inheritance system require a particular kind of mathematical framework.
[103] Other criticisms of the effort to frame culture in tandem with evolution have been leveled by Richard Lewontin,[104] Niles Eldredge,[105] and Stuart Kauffman.