Protein clock dating

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Violation of these conditions can lead to erroneous inferences and result in estimates that are off by orders of magnitude.

In this study, we examine the consistency of substitution rates among a set of conserved genes in diverse bacterial lineages, and address the questions regarding the validity of molecular dating.

Although there is some uncertainty in the clock, this dating may pose a problem for the widely believed hypothesis that the bipedal creature, which lived some 3.7 million years ago at Laetoli in Tanzania and at Hadar in Ethiopia, was ancestral to man and evolved after the human-ape splitting.

Another likelier possibility is that mt DNA was transferred through hybridization between a proto-human and a protochimpanzee after the former had developed bipedalism.

One also assumes that all the sand is in the bottom of the glass when one turns it over. He must look for something in the bone which disappears over time, as the sand disappeared from the top chamber of the egg timer.

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This use of molecular clocks is based on the assumptions that substitution rates for homologous genes or sites are fairly constant through time and across taxa.

Kumar S, Filipski A, Swarna V, Walker A, & Hedges SB. Placing confidence limits on the molecular age of the human-chimpanzee divergence. Assessing the quality of molecular divergence time estimates by fossil calibrations and fossil-based model selection. Comparison of likelihood and Bayesian methods for estimating divergence times using multiple loci and calibration points, with application to a radiation of cute-looking mouse lemur species.

Proceedings of the National Academy of Sciences 1842-18847. Philosophical Transactions of the Royal Society of London B 377-1483.

The molecular clock of mitochondrial DNA (mt DNA) was calibrated by setting the date of divergence between primates and ungulates at the Cretaceous-Tertiary boundary (65 million years ago), when the extinction of dinosaurs occurred.

A generalized leastsquares method was applied in fitting a model to mt DNA sequence data, and the clock gave dates of 92.3±11.7, 13.3±1.5, 10.9±1.2, 3.7±0.6, and 2.7±0.6 million years ago (where the second of each pair of numbers is the standard deviation) for the separation of mouse, gibbon, orangutan, gorilla, and chimpanzee, respectively, from the line leading to humans.

By tipping the glass when the egg starts cooking, one learns when three minutes are up and the boiling should be stopped.

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