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ABSTRACT

Whales, dolphins and porpoises, 80 species of entirely aquatic mammals, constitute the order Cetacea. In the early Eocene, about 55 to 60 million years ago according to paleontologists, distant ancestors of modern cetaceans left land for aquatic life. Cetaceans are diverse; average adult size of cetacean species varies by 1000 to 2000 times. Small and large species occupy all oceans from the equator to the polar seas, some forms inhabit rivers and four species live only in fresh water.

Cetaceans are born in water and spend their entire lives in the aquatic medium. There is a great gap in knowledge about hearing in most cetacean species and especially about how noise and high-intensity sound may affect all cetaceans and other mammals underwater. Studies of temporary threshold shift (TTS) and occupational noise exposure in human divers suggest a cautious approach to cetacean noise exposure until data on cetacean TTS can give us some idea of the dynamic range of cetacean ears.  相似文献   

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Tännsjö T 《Bioethics》1992,6(4):288-296
Is it defensible that society spends money on medical or research projects intended to help people solve their fertility problems? Suppose that we want to answer this question from the point of view of a utilitarian cost-benefit analysis. The answer to the question then depends, of course, on how expensive these projects turn out to be, relative to the costs of other possible projects. But it depends also on how we assess the benefits of these projects. To whom do they accrue? Who are the beneficiaries of these projects?  相似文献   

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R. M. Johnstone 《CMAJ》1931,24(4):580-581
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Our view of sperm competition is largely shaped by game-theoretic models based on external fertilizers. External fertilization is of particular interest as it is the ancestral mode of reproduction and as such, relevant to the evolution and maintenance of anisogamy (i.e., large eggs and tiny, numerous sperm). Current game-theoretic models have been invaluable in generating predictions of male responses to sperm competition in a range of internal fertilizers but these models are less relevant to marine broadcast spawners, the most common and archetypal external fertilizers. Broadcast spawners typically have incomplete fertilization due to sperm limitation and/or polyspermy (too many sperm), but the effects of incomplete (<100% fertilization rates) fertilization on game-theoretic predictions are unclear particular with regards to polyspermy. We show that incorporating the effects of sperm concentration on fertilization success changes the predictions of a classic game-theoretic model, dramatically reversing the relationship between sperm competition and the evolutionarily stable sperm release strategy. Furthermore, our results suggest that male and female broadcast spawners are likely to be in conflict at both ends of the sperm environment continuum rather than only in conditions of excess sperm as previously thought. Across the majority of the parameter space we explored, males release either too little to too much sperm for females to achieve complete fertilization. This conflict could result in a coevolutionary race that may have led to the evolution of internal fertilization in marine organisms.  相似文献   

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RIVKA WEINBERG 《Bioethics》2013,27(9):471-484
In formulating procreative principles, it makes sense to begin by thinking about whose interests ought to matter to us. Obviously, we care about those who exist. Less obviously, but still uncontroversially, we care about those who will exist. Ought we to care about those who might possibly, but will not actually, exist? Recently, unusual positions have been taken regarding merely possible people and the non‐identity problem. David Velleman argues that what might have happened to you – an existent person – often doesn't merit moral consideration since the alternative person one would have been had what might have happened actually happened is a merely possible person about whom one has no reason to care. He argues that his way of thinking can eliminate the non‐identity problem. Caspar Hare argues that merely possible people have interests and are morally relevant. He argues that we can solve the non‐identity problem by rejecting the view that merely possible people are morally irrelevant. Both Hare and Velleman argue that focusing on one's de dicto rather than on one's de re children can help us avoid the non‐identity problem. I analyze the role that merely possible, nonexistent hypothetical entities ought to play in our moral reasoning, especially with regard to procreation. I refute both Velleman's and Hare's views and demonstrate the difficulties we encounter when we try to apply their views to common non‐identity cases. I conclude with the common‐sense view regarding who matters, morally: only those who do, did, or will exist.  相似文献   

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Reid L 《Bioethics》2005,19(4):348-361
The seriousness of the risk that healthcare workers faced during SARS, and their response of service in the face of this risk, brings to light unrealistic assumptions about duty and risk that informed the debate on duty to care in the early years of HIV/AIDS. Duty to care is not based upon particular virtues of the health professions, but arises from social reflection on what response to an epidemic would be consistent with our values and our needs, recognizing our shared vulnerability to disease and death. Such reflection underwrites a strong duty of care, but one not to be borne solely by the altruism and heroism of individual healthcare workers.  相似文献   

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