a86 



NATURE 



[December 28, 



191 1 



therefore be f ' ■ ' •*•*'• r^'>sqirito reduction when 



the malaria- 



Dr. C. A. I ...lied a very good report 



on malaria in !'■ '1 its prevention. He con- 



cludes that, as u : 'St from the first, the prin- 



cipal measure must be the reduction of the carrier, 

 H. stephensi. The cost should be about 100,000 rupees 

 a year. Our studies of malaria are, then, advancing 

 into fine detail; but I agree with Colonel Kin^^, C.I.E., 

 that practical preventive measures should not be post- 

 poned until we actually become quite omniscient. That 

 will imply a considerable loss of life in the meantime. 

 We have already waited twelve years in India. 



R. Ross. 



THE LONGEVITY OF ANIMALS.' 



ONE of the most satisfactory results of the re- 

 organisation of the Zoological Society of London 

 is the series of papers dealing with important aspects 

 of animal life which are now issuing from the pens 

 of the society's officials. Instead of being content to 

 amass, as formerly, a mere collection of as many 

 strange beasts as possible for the inspection of the idle 

 and curious, the otlicials are now directing their atten- 

 tion to many important points concerning the life of 

 animals which could not have been examined, except 

 where such unrivalled opportunities exist for their 

 prosecution. Thus the Gardens bid fair to become a 

 centre for important studies, while the health of the 

 animals improves as the results are brought to bear 

 on their treatment and housing. 



In a recent paper Dr. Chalmers Mitchell has col- 

 lected the available information supplied by records 

 in the Gardens concerning the length of life and 

 viability of mammals and birds. 



On first glancing at this paper we are struck by 

 the immense amount of information collected, and, 

 on the other hand, by the small amount of knowledge 

 which we really possess on so important a subject. 



This deficiency is not likely to be easily eliminated, 

 since our powers of ascertaining the actual length of 

 life of any wild animal are, and must always remain, 

 strictly limited. Sometimes an individual animal be- 

 comes abnormally marked, so that we observe and 

 watch it for a period, or the unnatural life of a captive 

 affords us material for estimating the longevity of the 

 wild race; but such isolated observations can at 

 the best only be regarded as approximate, and our 

 knowledge of the longevity of the bulk of wild animals 

 must always remain meagre. 



Even our knowledge of the longevity of common 

 domestic animals is far below the standard which 

 might be expected. Domestic fowls are said by Dr. 

 Mitchell to be capable of living for thirty years, yet, 

 owing to commercial reasons, few members of the 

 farmyard flock reach five years. It is the same with 

 cattle. Although their potential longevity is, accord- 

 ing to Dr. Mitchell, about thirty years, we habitually 

 kill all our beef cattle and bulls under five, and a vast 

 majority of our cows under twelve years. The same 

 principle holds with all domestic breeds, the tendency 

 being to speed up the processes of life to such an 

 extent that the career of the organism is concluded 

 at an artificially early date. 



On the other hand, there are methods which may 

 eventually yield a considerable increase of Icnowledge, 

 and one of these is used by Dr. Mitchell, who has 

 tabulated the numerous records kept in the prosec- 

 toriuro of the Zoological Society, and has calculated 



wLl'2.''.^*'^''"'"?, Relative Viabilitv in Mammals .ind Birds: with » 

 l«^,!?J.«A. 7^".°' f^^^'^'.y"' By Dr. P. Chalmers Mitchell. F.R.S., 



^i^!:z^t. ''^xt^^t^z:"' '""'*'"• ^""^ '*"• ^*=- ^' ^ 



NO. 2200. VOL. 88] 



the average and maximum longevity of a lar^'- " ' - 



of mammals and birds which have lived ui. 



the Gardens. From these it appears that tlu „t, 



duration of life of any species in the Gardens is a^ 

 a rule remarkably below the maximum dumtinn s< 

 that, to the majority of animals, captivity, i 

 the care of experts and in spite of the resi: 

 tection from enemies, is anything but coi. 

 great length of life. Even, however, after ^ 



for the undoubted shortening of life resulting from 

 ciptivity, the potential longevity of mammals in 

 general appears to be surprisingly low, and it ma: 

 be some satisfaction to know that the possible dura- 

 tion of life in man is probably greater than that 01 

 any other mammal, excepting, possibly, the large 

 whales. 



In this respect birds seem to be fully equal, if not 

 superior, to mammals, amongst which those who liv< 

 longest are certain of the larger carnivora and un- 

 gulates. For instance, the potential longevity 01 

 lions is between thirty and forty years; a polar 

 bear lived to thirty-three years in the Gardens, and 

 the largest ungulates may reach fifty years. 



Both whales and elephants are popularly supposed 

 to be creatures of high potential longevity, but as 

 regards the former, the officials of the Zoological Gar- 

 dens are naturally not in a position to offer any 

 information. As regards the latter, it appears that 

 their reputation has been wrongly acquired, since for 

 them Dr. Mitchell estimates one hundred years as 

 being the probable limit, and twenty to thirty years a 

 fair average duration. On the other hand, there are 

 amongst birds several groups which equal or exceed 

 such figures. A raven has been known to reach 

 sixty-nine years, an eagle sixty-eight, while more than 

 one parrot has been recorded to have survived to 

 close upon or more than a centurj-. It appears that 

 some birds of prey may also reach 100, and that 

 herons, swans, and geese have a high potential 

 longevity. The ostrich, to judge by its size, ought 

 to live as long as any other bird, but thirty-five years 

 is considered to be an extreme age for it. 



The most difficult mammals to keep in captivity are 

 probably the insectivorous bats. For these the maxi- 

 mum duration of life in the Gardens has so far been 

 only five months, but the failure to keep them alive 

 is undoubtedly due, not to their being naturally short- 

 lived animals, but to their great delicacy under arti- 

 ficial conditions. 



These bats commence to breed at relatively so late 

 a period of their life and produce so few young at a 

 time or in any single season that the majority of them 

 must in nature reach an age of at least five years, 

 that is, if they are to keep up their numbers and 

 w-ithout making any allowance for the undoubtedlv 

 high death-rate which is alwavs prevalent amongst 

 wild animals. Dr. Mitchell has calculated the death- 

 rate for the London sparrows at at least 50 per cent, 

 m a stationary population ; in the mixed assemblance 

 of vertebrates in the Zoological Gardens it has been 

 observed to be 28 per cent., both of which figures are 

 very much above that of human beings. 



Weissman has sought to establish a correlation 

 between longevity and reproduction, but Dr. Mitchell 

 refuses to accept his interpretation. He believes, not 

 that longevity has become adapted to reproduction, 

 but that the rate of reproduction has been adapted 

 to average specific longevity. In anv case, the death- 

 rate amongst prolific wild animals maintaining a 

 stationary population must be stupendous ; for instance, 

 if a mouse produces only two litters a vear of six 

 young in each, then if all survive to ma'turitv there 

 will be fourteen mice where before there were only 

 two, and if the population is to remain stationary 



