There are valves in the vessels that prevents backflow, just like in the viens. ... the lymph vessels to ensure that the flow of lymph
Sure. Single-cell organisms include bacteria and hens' eggs.
This is an example of microevolution.
Microevolution represents a small change in the genetic structure of the population. These changes manifest through the change in the allele frequencies of genes like in the case of dung beetles.
The causes of microevolution are evolutionary mechanisms, natural selection, genetic drift, mutations and gene flow.
Some isotopes, however, decay slowly, and several of these are used as geologic clocks. Dating rocks by these radioactive timekeepers is simple in theory, but the laboratory procedures are complex. <span>All methods rely on the fact that certain elements (particularly uranium and potassium) contain a number of different isotopes whose half-life is exactly known and therefore the relative concentrations of these isotopes within a rock or mineral can measure the age.</span>
