Red Queen: from populations to taxa and communities.

Biotic interactions via the struggle for control of energy and the interactive effects of biota with their physical environment characterize Van Valen's Red Queen (VRQ). Here, we review new evidence for and against a VRQ view of the world from studies of increasing temporal and spatial scales. Interactions among biota and with the physical environment are important for generating and maintaining diversity on diverse timescales, but detailed mechanisms remain poorly understood.

Gradual dinosaur extinction and simultaneous ungulate radiation in the hell creek formation.

Dinosaur extinction in Montana, Alberta, and Wyoming was a gradual process that began 7 million years before the end of the Cretaceous and accelerated rapidly in the final 0.3 million years of the Cretaceous, during the interval of apparent competition from rapidly evolving immigrating ungulates. This interval involves rapid reduction in both diversity and population density of dinosaurs.

Homology and causes.

Homology is resemblance caused by a continuity of information. In biology it is a unified developmental phenomenon. Homologies among and within individuals intergrade in several ways, so historical homology cannot be separated sharply from repetitive homology.

The archaebacteria and eukaryotic origins.

Critical analysis of the phylogeny of prokaryotes is in its infancy. Woese and others have made the startling proposal that methane-producing bacteria and a few others form a phyletically unified group, the Archaebacteria, as old and as diverse (although not now as numerous) as all other bacteria. The only critique of this proposal is inadequate.

The history and stability of atmospheric oxygen.

There are three processes weakly concentration-dependent that keep changes in concentration of atmospheric pressure from being a random walk-inhibition of net photosynthesis by oxygen, the passage of hydrogen through the oxidizing part of the atmosphere before it escapes from the earth, and burial of reduced carbon in anaerobic water. A stronger regulator seems desirable but remains to be found. The cause of the initial rise in oxygen concentration presents a serious and unresolved quantitative problem.