Daisyworld is Darwinian: constraints on adaptation are important for planetary self-regulation.

The Daisyworld model demonstrates that self-regulation of the global environment can emerge from competition amongst types of life altering their local environment in different ways. Robertson & Robinson (1998. J. theor. Biol.195, 129-134) presented what they describe as a "Darwinian Daisyworld" in which the ability of organisms to adapt their internal physiology in response to environmental change undermines their ability to regulate their environment. They assume that there are no bounds on the environmental conditions that organisms can adapt to and that equal growth rates can potentially be achieved under any conditions. If adaptation could respond sufficiently rapidly to changes in the environment, this would eliminate any need for the environment to be regulated in the first place, because all possible states of the environment would be equally tolerable to life. However, the thermodynamics, chemistry and structure of living organisms set bounds on the range of environmental conditions that can be adapted to. As these bounds are approached, environmental conditions limit growth rate, and adaptations necessary for survival can also cost energy. Here we take account of such constraints and find that environmental regulation is recovered in the Daisyworld model. Hence, we suggest that constraints are an important part of a self-regulating planetary system.

Midwife to the greens: the electron capture detector.

James E. Lovelock makes an account of the path he has followed since he started his scientific research at the National Institute for Medical Research (NIMR) in London in the 1940s, emphasizing the aspects related to environmental sciences. Lovelock explains the origins of the electron capture detector (ECD). So far, the ECD is the most sensitive, easily portable and inexpensive analytical apparatus capable of detecting substances present in the atmosphere at concentrations as low as parts per trillion (10(-12)). It has been the first device specifically sensitive to pollutants, and its use has provided the grounds for the development of environmental sciences, and green politics. The data gathered by the ECD about the persistence of pesticides in the environment led American biologist Rachel Carson to write her seminal book Silent Spring; data regarding the global presence of chlorofluorocarbons (CFC) in the atmosphere led Sherwood Rowland and Mario Molina to develop their theory of ozone depletion. The results of his research over the years led Lovelock himself to the development of the Gaia theory.

Exploiter-mediated coexistence and frequency-dependent selection in a numerical model of biodiversity.

The key feature of the Daisyworld approach is to explicitly model feedbacks between the competitive dynamics of a planetary biota (daisies with different albedos) and the planet's climate, namely its surface temperature. Self-regulation of surface temperature and stable population dynamics are striking emergent properties of this system, despite increasing energy output from the model's sun. In this paper we attempt to perturb Daisyworld by introducing herbivores endowed with one of four strategies for feeding on daisies in a system rich in daisy diversity, and find that the herbivores only moderately diminish the temperature regulating abilities of the system. Furthermore, we find that the precise trajectory of the system's temperature regulation depends critically on which daisy species the herbivore allows to co-exist, thereby revealing that climate and patterns of biodiversity are highly interrelated in this model, and, possibly, in the real world.

Long-term results of open meniscal repair.

The purpose of this study was to document the long-term clinical and radiographic results of open meniscal repair. Thirty consecutive patients, involving 33 open repairs, were evaluated by history, physical examination, KT-1000 arthrometer testing, Lysholm II score, Tegner activity score, and weightbearing radiographs. The mean followup was 10.9 years (range, 10.1 to 13). No patients were lost to followup. Seven meniscal retears (21%) were documented (six demonstrated by repeat arthroscopy and one suspected on clinical evaluation). Three of 21 (14%) acute repairs (performed within 6 weeks of injury) retore as compared with 4 of 12 (33%) chronic repairs (P = 0.38). None of the 12 menisci in stable knees (< 3 mm side-to-side difference in anterior laxity on manual maximum load testing) sustained retears, compared with 7 of 21 (33%) menisci in nearly stable or unstable knees (P = 0.03). Standing radiographs revealed no degenerative changes in 22 of 26 (85%) compartments with successful repairs as compared with 3 of 7 (43%) compartments with retorn menisci (P = 0.04). We concluded that the long-term survival rate of repaired menisci was 79%, that increased retear rates were encountered in unstable knees, and that radiographs provided evidence for the biomechanical function of successful meniscal repairs.

New statements on the Gaia theory.

Gaia is the name the ancient Greeks gave to their goddess of the Earth and is the root of words like geography and geology. Gaia is also a straightforward scientific theory about the Earth and the organisms that inhabit it. Gaia theory is testable and has a proper mathematical basis in a set of closely coupled differential equations. We do not yet know if it is a good explanation of the way our planet works; the evidence is only partially gathered. Its main value at this stage is to provide a different way to look at the Earth. In science, Gaia theory has already led to significant discoveries but just as important it forces us to question whether the good of humankind is the only thing that matters. The true value of the journeys into space was to reveal the Earth as a live planet. They made us realise for the first time that humanism is not enough. The view from space teaches that we are part of a greater entity, the Earth, and that our survival and its good health are inextricably entwined. Perhaps in time we can expand our view to encompass the larger systems of the galaxy and the Universe. Now the Earth needs our full attention.

The surgical treatment of arthrofibrosis of the knee.

Sixty-one lysis of adhesion procedures were performed for arthrofibrosis of the knee between 1981 and 1990. In 43 cases (37 patients) the etiology was prior knee ligament surgery. Ten cases had sustained fractures about the knee and eight had miscellaneous etiologies. Six patients required a second lysis of adhesion procedure. A retrospective analysis of the 43 ligament patients was undertaken to evaluate the results of surgical treatment. All 43 cases were available for followup at an average of 3.6 years. Surgical indications included flexion or extension deficits of > or = 10 degrees or when motion failed to improve despite 2 months of intense therapy. Follow-up assessment included clinical and radiographic evaluation. Flexion improved from 83% to 97% of the contralateral side. Extension deficits improved from 14 degrees to 3 degrees. Only 23 of 37 patients (62%) achieved satisfactory functional results. Radiographic evidence of degenerative changes, soft tissue calcification, and patella infera was found in 89%, 51%, and 9% of the patients, respectively. Patients requiring surgical treatment for arthrofibrosis after knee ligament surgery achieved excellent motion gains, but functional outcome scores were compromised and radiographic findings were concerning. Patients with the localized anterior intraarticular variant or those undergoing lysis of adhesion surgery sooner than 6 months had outcomes comparable with controls.

The normal posterior atlantoaxial relationship.

The relationship of the posterior aspects of the atlas and the axis were studied in 100 normal adult volunteers. The ratio of the height of the atlantal spinolaminar line to the atlantoaxial interspinous distance was found to be remarkably constant and was less than 2.0 in all men and women. This ratio should prove helpful in detecting hyperflexion injuries isolated to the atlantoaxial level.

Bone formation following carpal interposition arthroplasty.

Two cases of bone formation occurring at the site of carpal excision and soft tissue interposition are presented.

Complications of total knee replacement.

The records and radiographs of 162 patients with 224 total knee replacements were reviewed for evidence of complications. Early complications included cardiovascular abnormalities, in particular deep vein thrombosis (3%), and limitation of motion requiring manipulation under anesthesia (7%). Late problems included patellofemoral arthritis (11%), heterotopic bone formation (10%), loosening (7%), deformity (4%), fracture (3%), and infection (2%). Patellofemoral pain and arthritis is the most common and often the most disabling complication.

The radiology of total hip replacement.

The radiology of total hip replacement (THR) and its complication is reviewed in conjunction with a long-term follow-up study on 402 patients with 501 prostheses. The indications, contraindications, biomechanics, and operative management of these patients is discussed. Clinical complications such as deep vein thrombosis, pulmonary embolism, and hemorrhage are mentioned. Postoperative infections including granulomatous pseudotumors, dislocations and fractures, true loosening of the prosthesis, and heterotopic bone formation (HBF) are discussed and illustrated. The importance of differentiating the lucent line from true loosening is stressed. Mechanical and other clinical complications which are largely ignored by radiologists are also discussed. The uses of arthrography and bone scanning are included.

Central acetabular fracture dislocations: an unusual complication of seizures.

Central acetabular fracture-dislocations resulting from convulsions are rare. The literature is reviewed in this regard and we add two additional cases in which hyponatremia was the cause of seizure activity. In most cases this type of injury is seen in bone already weakened by underlying disease.

Halogenated hydrocarbons in the atmosphere.

The sources, sinks, and tropospheric abundancies of the gaseous halocarbons, so far as they are known, are listed and discussed. The relative importance of natural and of man-made halocarbons is discussed within the context of contemporary concern about the depletion of stratospheric ozone by chlorine-bearing compounds.