The rise and fall of SRY

Comparisons between species reveal when and how SRY, the testis-determining gene, evolved. SRY is younger than the Y chromosome, and so was probably not the original mammal sex-determining gene that defined the Y. SRY is typical of genes on the Y chromosome. It arose from a gene on the proto-sex chromosome pair with a function (possibly brain-determination) in both sexes. It has been buffeted in evolution, and shows variation in copy number, structure and expression. And it is dispensable, having been lost at least twice independently in different rodent lineages. At the observed rate of attrition, the human Y chromosome will be gone in 5-10 million years. This could lead to the extinction of our species or to a burst of hominid speciation.     

The rise and fall of photomutagenesis

UV is the most abundant human carcinogen, and protection from extensive exposure to it is a widespread human health issue. The use of chemicals (sunscreens) for protection is intuitive and efficacious. However, these chemicals may become activated to reactive intermediates when absorbing energy from UV, thus producing damage themselves, which may manifest itself in phototoxic, photoallergenic or photocarcinogenic reactions in humans. The development of safe sunscreens for humans is of high interest. Similar issues have been observed for some therapeutically used principles such as PUVA therapy for psoriasis or porphyrins for phototherapy of human cancers. Photoactivation has also been reported as a side effect of various pharmaceuticals such as the antibacterial fluoroquinolones. In this context, the authors have been involved over more than 20 years in the development and refinement of assays to test for photomutagenicity as an unwanted side effect of UV-mediated activation of such chemicals for cosmetic or pharmaceutical use. The initial years of great hopes for simple mammalian cell-based assays for photomutagenicity to screen out substances of concern for human use were followed by many years of collaborative trials to achieve standardization. However, it is now realized that this topic, albeit of human safety relevance, is highly complex and subject to many artificial modifiers, especially in vitro in mammalian cell culture. Thus, it is not really suitable for being engineered into a general testing framework within cosmetic or pharmaceutical testing guidelines. Much knowledge has been generated over the years to arrive at the conclusion that yes, photomutagenicity does exist with the use of chemicals, but how to best test for it will require a sophisticated case-by-case approach. Moreover, in comparison to the properties and risks of exposure to UV itself, it remains a comparatively minor human safety risk to address. In considering risks and benefits, we should also acknowledge beneficial effects of UV on human health, including an essential role in the production of Vitamin D. Thus, the interrelationships between UV, chemicals and human health remain a fascinating topic of research.     

The fall and rise of apical dominance

The plant hormone auxin, synthesised in the shoot apex, moves down the stem and inhibits lateral branching. Auxin does not travel upward into the branches, so it must act indirectly; for example, through a second messenger. However, recent work on auxin transport suggests a possible additional mechanism whereby auxin transport in the stem prevents the establishment of auxin transport out of the branches, inhibiting their growth.     

The rise and fall of mutator bacteria

Bacteria with elevated mutation rates are frequently found among natural isolates. This is probably because of their ability to generate genetic variability, the substrate for natural selection. However, such high mutation rates can lead to the loss of vital functions. The evolution of bacterial populations may happen through alternating periods of high and low mutation rates. The cost and benefits of high mutation rates in the course of bacterial adaptive evolution are reviewed.     

The rise and fall of forensic hypnosis

This paper examines the fortunes of the controversial use of hypnosis to ‘enhance’ autobiographical memories in postwar America. From the 1950s through the early 1980s, hypnosis became increasingly popular as a means to exhume information thought to be buried within the mind. This practice was encouraged by lay understandings of memory drawn from a material culture full of new recording devices (motion pictures, tape and then video recorders); and during the years when the practice was becoming most popular and accepted, academic psychologists developed a contrary, reconstructive, account of memory that was put to use in a series of battles meant to put an end to hypnotic recall. But popular commitment to the idea of permanent memory ‘recordings’ sustained the practice and the assumptions about memory and self that were associated with it, and in the face of a culture of academic psychology fully committed to the idea of ‘reconstructive’, malleable memory, a tidal wave of ‘enhanced’ memories swept America in the late 1980s and 1990s, in the so-called ‘memory wars’. These, in turn, provoked academic psychologists to research the claims and counter claims central to the memory wars. The paper will also make an argument about the importance of lay knowledge in the psychological sciences explored in this paper: that popular psychological beliefs played a significant, even formative role in defining the nature of forensic psychological expertise, and also the framing of elite academic psychological research.     

The rise and fall of the RNA world.

It is generally believed that there was a time when life on earth was based on RNA rather than on DNA and protein. Considering the relevant evidence from geophysics, geology, paleobiology, and molecular biology, it is possible to set the time frame for the existence of RNA-based life to a 400 million year interval beginning 4.0 to 4.2 billion years ago and ending 3.6 to 3.8 billion years ago. The minimum level of biochemical complexity that existed during this time consists of those functions necessary for the establishment and maintenance of an RNA-based evolving system, namely, an RNA unwinding activity, an RNA replicase activity, and a primitive biosynthetic apparatus leading to enrichment of the local environment with activated D mononucleotides.     

The rise and fall of antimicrobial resistance.

Antimicrobial resistance is a growing problem in nearly every infectious disease, but the extent and rate of increase of the problem varies widely with different pathogen-drug combinations. The rate of increase of resistance depends primarily on the availability of resistant variants and the intensity of selection imposed by antimicrobial treatment (appropriately measured). Declines in resistance following antimicrobial control measures are typically faster in hospital-acquired infections than in community-acquired ones, probably owing to the dependence in the latter case on the fitness cost of resistance. Open questions and approaches for testing the hypotheses proposed here are outlined.     

The rise and fall of Hox gene clusters

Although all bilaterian animals have a related set of Hox genes, the genomic organization of this gene complement comes in different flavors. In some unrelated species, Hox genes are clustered; in others, they are not. This indicates that the bilaterian ancestor had a clustered Hox gene family and that, subsequently, this genomic organization was either maintained or lost. Remarkably, the tightest organization is found in vertebrates, raising the embarrassingly finalistic possibility that vertebrates have maintained best this ancestral configuration. Alternatively, could they have co-evolved with an increased ;organization' of the Hox clusters, possibly linked to their genomic amplification, which would be at odds with our current perception of evolutionary mechanisms? When discussing the why's and how's of Hox gene clustering, we need to account for three points: the mechanisms of cluster evolution; the underlying biological constraints; and the developmental modes of the animals under consideration. By integrating these parameters, general conclusions emerge that can help solve the aforementioned dilemma.     

The rise and fall of Homo sapiens sapiens

Human beings have broken the ecological 'law' that says that big, predatory animals are rare. Two crucial innovations in particular have enabled us to alter the planet to suit ourselves and thus permit unparalleled expansion: speech (which implies instant transmission of an open-ended range of conscious thoughts) and agriculture (which causes the world to produce more human food than unaided nature would do). However, natural selection has not equipped us with a long-term sense of self-preservation. Our population cannot continue to expand at its present rate for much longer, and the examples of many other species suggests that expansion can end in catastrophic collapse. Survival beyond the next century in a tolerable state seems most unlikely unless all religions and economies begin to take account of the facts of biology. This, if it occurred, would be a step in cultural evolution that would compare in import with the birth of agriculture.     

The rise and fall of Darwin's second theory

Conclusion The difficulty of discussion between people brought up in different frameworks is to be admitted, Karl Popper writes. But nothing is more fruitful than such a discussion; than the culture clash which has stimulated some of the greatest intellectual revolutions.⁷¹ Certainly Kirby and Darwin were brought up in different cultures — Kirby with his Anglican-Tory orientation, Darwin with his Whig-liberal background — and certainly the clash generated some interesting theories; but it also resulted in the revival of Lamarck's discredited habit theory, which took another century of careful experimentation to weed out.     

The rise and fall of the chemoattractant receptor GPR33

Chemokine and chemoattractant receptors are members of the large superfamily of G protein-coupled receptors (GPCR), which control leukocyte chemotaxis. In addition to their physiological role, several chemokine and chemoattractant receptors, such as CCR5 and Duffy, have been directly associated with pathogen entry. GPR33 is an orphan chemoattractant GPCR that was previously identified as a pseudogene in humans. GPR33 evolved in mammals about 125-190 million years ago. The cloning and analysis of more than 120 mammalian GPR33 orthologs from 16 of 18 eutherian orders revealed an inactivation of this chemoattractant GPCR not only in humans, but also in several great ape and rodent species. Intriguingly, in all ape and some rodent species where the inactivation occurred, samples harbored both pseudogene and intact gene variants. The analysis of over 1200 human individuals representing all major linguistic groups revealed that the intact allele of GPR33 is still present in the human population. Estimates of the age of the human alleles suggest inactivation in the past 1 million years. Similarly, analysis of more than 120 wild-caught gray rats (Rattus norvegicus), revealed that inactivation of gpr33 is worldwide fixed and occurred in less than 0.7 million years ago. The coincidental inactivation and its fixation in several species of distantly related mammalian orders suggest a selective pressure on this chemoattractant receptor gene.