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Thus, given these forces that can act against cultural change, one can ask what is the characteristic pace of cultural evolution, and how does it compare to the pace of biological evolution? In this study, I try to answer these questions by comparing the rates of change in technologies, as observed in the historical and archaeological record to the rates of morphological change, as seen in contemporary and fossil animal populations. Biological rates were obtained from previously analyzed data sets [28] , [29].

Biological rates are calculated from observations made at various taxonomic levels, ranging from subpopulations of the same species to genus and family. Cultural rates were compiled from the archaeological literature and are described in Table 1. Cultural rates are based on observations made at the level of taxonomic unit that archaeologists often refer to, albeit haphazardly [30] as types, classes, and style; that is, artifacts that share a combination of attributes and that have distinct spatial and temporal distribution.

Only rates corresponding to a change in one-dimensional metric attributes were collected. Biological rates observed in a laboratory or human-perturbed settings, as well as those measuring divergence between contemporary sister populations, were excluded. Effort was made to assemble an unbiased sample of cultural rates calculated from what the author s of each study interpreted as historically continuous populations.

Both biological and cultural rates were measured in darwins d , which is a standardized unit of change in factors of e , the base of the natural logarithm, per millions of years. The darwin is preferred to the haldane [31] , which is another metric of the rate of evolutionary change, since standard deviations for metric attributes are often not reported in the archaeological literature and because the generation time for cultural evolution is unclear.

The rates analyzed in this study were absolute and non-autonomous [28] , [32]. Biological rates are clustered by studies, taxonomic units, subpopulations if relevant , and traits.

Cultural rates are clustered by studies, technologies, and traits. To test for the interaction between the type of rates biological or cultural or rate and time intervals or rate ages , a linear mixed model of interaction was used.

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Applying Evolutionary Archaeology: A Systematic Approach

Time interval was assigned as a fixed effect and study-series as a random effect using an unstructured covariance matrix. The linear mixed model controls for the fact that rates are unevenly distributed among the different studies. Comparing cultural rates of change to biological rates that are calculated from various organisms on an absolute time scale allows us to compare the ability of human culture and biological traits to keep pace with a common driver, such as climate change.

Historical contingencies can influence evolution [33] — [35] , and both biological and cultural traits can be subjected to a wide range of evolutionary forces, including neutral drift and selection [8]. In order to circumvent this problem and to obtain the typical pace of biological and cultural evolution, I compare large samples of rates representing a wide range of biological and cultural traits that have undoubtedly been subjected to different regimes of evolutionary forces and historical contingencies. Archaeological rates are on average faster than biological rates, with the fastest cultural rates observed being more than twice as large as the fastest biological rates Fig.

However, a comparison of rates, as presented in Figure 1 , is complicated by the fact that rates of biological evolution are inversely correlated with the time interval over which change is measured [2] , [8] , [28] , [38] — [41]. Evolution appears to operate faster when observing short intervals of time compared to long intervals of time. Two main reasons for this dependency have been suggested [28] , [38] — [40] , [42] — [45]. First, as the time interval of observation increases, it becomes more likely that the net rate observed is in fact averaged over several disparate rates and evolutionary reversals.

How Do Archaeologists Decide Where to Dig? - Introduction to Archaeology

This effect is in part driven by the fact that the taxonomic level of the data is likely to increase with the observation time interval. This is true for both biological and cultural evolution. The level of taxonomic units impacts rates of evolution because the evolutionary change that occurs below a taxonomic level i. This is accomplished by plotting the rates on an ln -rate versus ln -time interval graph, and using the linear model that best describes the correlation to compare the groups of rates on the same temporal scale [44].

A linear mixed model shows that cultural rates are also inversely correlated with the time interval over which they are measured Fig. As we study older periods of our history, taphonomic processes cause the measured time intervals to increase [46]. Cultural rates are therefore inversely correlated with their absolute age Fig. This correlation could potentially account for one of the most salient features of the archaeological record: the pace of change of human material culture appears faster in more recent periods than it does for older ones.

Biological rates black circles and cultural rates gray squares are inversely correlated to the interval of the time over which the rates are measured. The solid lines represent the linear mixed model of interaction that best fit the biological black line and cultural gray line distributions Table 2. The age of a rate corresponds to the midpoint, in years Before Present BP , of the time interval over which the rate is calculated. The solid line represents the linear mixed model of interaction of rates with age Table 3. The difference between cultural and biological rates remains significant even when the effect of the measurement time intervals is controlled Table 2.

We can use the linear mixed model that describes each type of rate to compare them on the same temporal scale. The models converge at the time scale of approximately 1 month i. Cultural change is already recognizably faster at this time scale. At a larger time interval of years, which is the time scale of millennial climatic fluctuations [41] , [47] — [52] , the divergence is more pronounced, with morphologies changing at a pace of Thus, cultural evolution is faster than biological evolution when the effects of observational time intervals are controlled.

This is due to the fact that for any given time interval, the characteristic amount of accumulated changes x 2 — x 1 is greater for culture than for biology. This suggests that cultural change, like biological change, is a multiplicative process: the increments of change in a trait increase as the trait becomes larger. More surprising, however, is the fact that the magnitude of accumulated cultural changes grows at an increasingly faster pace with time, which is more so than the magnitude of accumulated biological change.

Figure 2 shows that the difference between rates of cultural evolution and biological evolution may appear small or even non-existent over a short time scale. This result is not an artifact of the bimodal distribution of the time intervals of biological rates. Removing the rates obtained from the paleontological record from the analysis, which account for the rightmost cloud of biological rates plotted in Figure 2 , actually increases both the distance between biological and cultural rates as well as the rate at which this difference increases with the time interval Table 4.

The observation that technologies can change over a short time scale, even if unnoticeably faster than animal morphologies, may be sufficient to make culture adaptive. The minimal time interval at which biological evolution can be observed depends on the generation time of the species. For instance, biological rates calculated over a very short time interval, as plotted in Figure 2 , come from species where the life span is counted in months.

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Several cultural rates have been observed over similarly short time scales, while the generation time of our species is approximately 20 years. Another way to look at this is to calculate evolutionary rates as change per generation, rather than as change per million years. To do this, I have assumed a generation length for humans of 20 years for the computation of cultural rates. The biological rates calculated from the fossil record were also excluded from the analysis, because we do not have good generation time estimates for them. This analysis shows that the pace of cultural change, per generation, is faster than the rate of biological evolution over all observation time intervals Fig.

Biological rates black circles and cultural rates gray squares , calculated as change per generation, are inversely correlated to the interval of the time over which the rates are measured. The solid lines represent the linear mixed model of interaction that best fit the biological black line and cultural gray line distributions Table 5. The conversion of rates from an absolute time scale to a generational time scale impacts mostly the biological rates from species with a short generation time.

For any given amount of phenotypic change observed over any given time interval, the difference between rate of change per millions of years and rates of change per generation time increases as generation time of species increases. This effect explains why the difference between the slopes of the two linear models, although significant, is smaller Table 5 than that shown in Figure 2. In this study, I aimed to test the hypothesis that the pace of cultural evolution is faster than the pace of biological evolution.

Michael J. O'Brien (Author of Archaeology as a Process)

I found that 1 Similar to biological rates, rates of cultural change are inversely correlated with the time interval over which they are measured; 2 this inverse correlation explains, at least in part, why the pace of change appears to be faster for more recent periods of the archaeological record; 3 when controlling for this inverse correlation, rates of cultural evolution are significantly faster than rates of biological evolution; 4 The magnitude of accumulated cultural change grows at an increasingly faster rate with time, which is greater than the magnitude of accumulated biological change.

This could mean that some of the adaptive benefits of cultural transmission are not reaped during the short term, but rather occur over longer time scales. However, the fact that biological rates decrease more rapidly with time interval could be driven in part by individual phenotypic plasticity.

Phenotypic plasticity is comparable to cultural evolution and allows organisms to change over short time intervals. It is possible that some of the biological rates calculated over a short time interval reflect rapid phenotypic change, while the changes observed over longer time intervals are mostly due to genetic change; and 5 the amount of cultural change observed per generation time 20 years is significantly faster than what we would expect from biological evolution for a species with the same generation time as humans.

This observation highlights the fact that culture allows us to evolve over time scales that are normally accessible only to short-lived species, while at the same time allowing us to enjoy the benefits of having a long life history, such as a large brain, an extended juvenile period, and long life span. However, it is likely that the archaeological record underestimates rates of cultural change over small time intervals compared to the fossil record. Correct measurements of evolutionary rates must be calculated using phylogenetically-linked populations.

Large and rapid changes can obscure phylogenetic relationships and lead to a loss of visibility of the most rapid changes from the data [28]. Fossil species are more likely to retain several homologous traits over longer periods of time compared to culturally transmitted technologies. This may allow for fossils to be compared despite a rapid evolution of other traits. The retention of trait homologies also allows fossils to be compared over greater spatial distances, which increases the chance that they have experienced divergent selective pressure and subsequently a greater morphological differentiation.

In contrast, it is often impossible to distinguish rapid cultural evolution in the archaeological record from population replacement. Because of this uncertainty, the cultural rates that were analyzed in this study originated from populations that remained in the same locality, with spatial propinquity being used as a measurement of historical continuity.


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