Phylogenetics and dating seriöse partnersuche Jena
Indirect dates are, however, associated with far greater uncertainties than direct dates.
Apart from the errors associated with the dating of the layer boundaries, reburial or mixing of deposits can lead to substantial errors.
Consequently, assigning a point value for the age of a layer-dated sample can be highly misleading.
In studies of ancient DNA from environmental samples, there is an additional risk of DNA migrating between strata (Haile et al. Sample-age uncertainties can be incorporated into Bayesian methods by specifying the prior age distribution of each ancient sample, rather than assigning a point value (Ho and Phillips 2009).
For example, samples can be contaminated with more recent sources of carbon, owing to either the dynamics of the depositional environment or during excavation and laboratory preparation (Mellars 2006).
Various sources of estimation error can reduce our ability to estimate rates and timescales accurately and precisely.
We show that, provided that samples have been accurately dated and have a broad temporal span, it might be unnecessary to account for sample-dating uncertainty in Bayesian phylogenetic analyses of ancient DNA.
We also investigated the sample size and temporal span of the ancient DNA sequences needed to estimate phylogenetic timescales reliably.
Calibrations are commonly based on paleontological or geological data, which can provide an estimate of the timing of divergence events (internal nodes) in the phylogenetic tree.
However, because of difficulties in assigning fossils to branches of the evolutionary tree, the placement of calibrations is often highly uncertain (Lee et al. In addition, internal-node calibrations can carry a substantial amount of temporal uncertainty, and it is usually difficult to quantify this (Ho and Phillips 2009).
Such risks can be assessed and minimized by replicating the dating process using different sections of the sample and by checking concordance with archeological or geological context (Törnqvist et al. As an alternative to radiocarbon dating, which is costly and involves destruction of the material being analyzed, samples can be dated indirectly.