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Иосиф Кубрак
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AlexK
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20.05.2001 10:41:03
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Рубрики
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Прочее;
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Re: Кубраку вопрос
Уважаемый Алекс,
Спасибо за сообщение. Его только что увидел, у Вас тут (или здесь на машине) дерево как-то прыгает, трудно следить и не могу
привыкнуть. :-)
*** О наследовании приобретённых признаков.
Источники? Основные положения? Эксперименты? ***
1. Источники.
Представления о наследовании приобретённых признаков имеют очень давние корни и встречаются в античности, средние века и
в эпоху Просвещения. Ради краткости отмечу два важных, на мой взгляд, этапа: начало 19-го века, когда идея была сформулирована
как часть теории эволюции Ламарком, и вторую половину 19-го века, когда она была пересмотрена Дарвином и включена в его
теорию эволюции в качестве одной из основных составляющих. Благодаря любезности Андрея, предоставившего ссылку на сайт,
на котором, в свою очередь, находились ссылки на сайты с работами Дарвина, я с удовольствием процитирую фрагмент из пятой
главы "Происхождения видов":
--------------------------------
Effects of Use and Disuse
From the facts alluded to in the first chapter, I think there can be little doubt that use in our domestic animals strengthens and enlarges certain parts, and
disuse diminishes them; and that such modifications are inherited. Under free nature, we can have no standard of comparison, by which to judge of the
effects of long-continued use or disuse, for we know not the parent-forms; but many animals have structures which can be explained by the effects of
disuse. As Professor Owen has remarked, there is no greater anomaly in nature than a bird that cannot fly; yet there are several in this state. The
logger-headed duck of South America can only flap along the surface of the water, and has its wings in nearly the same condition as the domestic
Aylesbury duck. As the larger ground-feeding birds seldom take flight except to escape danger, I believe that the nearly wingless condition of several
birds, which now inhabit or have lately inhabited several
oceanic islands, tenanted by no beast of prey, has been caused by disuse. The ostrich indeed inhabits continents and is
exposed to danger from which it cannot escape by flight, but by kicking it can defend itself from enemies, as well as any
of the smaller quadrupeds. We may imagine that the early progenitor of the ostrich had habits like those of a bustard, and
that as natural selection increased in successive generations the size and weight of its body, its legs were used more, and
its wings less, until they became incapable of flight.
Kirby has remarked (and I have observed the same fact) that the anterior tarsi, or feet, of many male dung-feeding beetles are very often broken off;
he examined seventeen specimens in his own collection, and not one had even a relic left. In the Onites apelles the tarsi are so habitually lost, that the
insect has been described as not having them. In some other genera they are present, but in a rudimentary condition. In the Ateuchus or sacred beetle
of the Egyptians, they are totally deficient. There is not sufficient evidence to induce us to believe that mutilations are ever inherited; and I should prefer
explaining the entire absence of the anterior tarsi in Ateuchus, and their rudimentary condition in some other genera, by the long-continued effects of
disuse in their progenitors; for as the tarsi are almost always lost in many dung-feeding beetles, they must be lost early in life, and therefore cannot be
much used by these insects.
In some cases we might easily put down to disuse modifications of structure which are wholly, or mainly, due to natural
selection. Mr. Wollaston has discovered the remarkable fact that 200 beetles, out of the 550 species inhabiting Madeira,
are so far deficient in wings that they cannot fly; and that of the twenty-nine endemic genera, no less than twenty-three
genera have all their species in this condition! Several facts, namely, that beetles in many parts of the world are very frequently blown to sea and perish;
that the beetles in Madeira, as observed by Mr Wollaston, lie much concealed, until
the wind lulls and the sun shines; that the proportion of wingless beetles is larger on the exposed Dezertas than in
Madeira itself; and especially the extraordinary fact, so strongly insisted on by Mr. Wollaston, of the almost entire
absence of certain large groups of beetles, elsewhere excessively numerous, and which groups have habits of life almost necessitating frequent flight;
these several considerations have made me believe that the wingless condition of so many Madeira beetles is mainly due to the action of natural
selection, but combined probably with disuse. For during thousands
of successive generations each individual beetle which flew least, either from its wings having been ever so little less
perfectly developed or from indolent habit, will have had the best chance of surviving from not being blown out to sea;
and, on the other hand, those beetles which most readily took to flight will oftenest have been blown to sea and thus have been destroyed.
The insects in Madeira which are not ground-feeders, and which, as the flower-feeding coleoptera and lepidoptera, must habitually use their wings to
gain their subsistence, have, as Mr. Wollaston suspects, their wings not at all reduced, but even enlarged. This is quite compatible with the action of
natural selection. For when a new insect first arrived on the island, the tendency of natural selection to enlarge or to reduce the wings, would depend on
whether a greater number of individuals were saved by successfully battling with the winds, or by giving up the attempt and rarely or never flying. As
with mariners ship-wrecked near a coast, it would have been better for the good swimmers if they had been able to swim still further, whereas it would
have been better for the bad swimmers if they had not been able to swim at all and had stuck to the wreck.
The eyes of moles and of some burrowing rodents are rudimentary in size, and in some cases are quite covered up by
skin and fur. This state of the eyes is probably due to gradual reduction from disuse, but aided perhaps by natural
selection. In South America, a burrowing rodent, the tuco-tuco, or Ctenomys, is even more subterranean in its habits
than the mole; and I was assured by a Spaniard, who had often caught them, that they were frequently blind; one which I
kept alive was certainly in this condition, the cause, as appeared on dissection, having been inflammation of the nictitating membrane. As frequent
inflammation of the eyes must be injurious to any animal, and as eyes are certainly not indispensable to animals with subterranean habits, a reduction in
their size with the adhesion of the eyelids and growth of fur over them, might in such case be an advantage; and if so, natural selection would constantly
aid the effects of disuse.
It is well known that several animals, belonging to the most different classes, which inhabit the caves of Styria and of
Kentucky, are blind. In some of the crabs the foot-stalk for the eye remains, though the eye is gone; the stand for the
telescope is there, though the telescope with its glasses has been lost. As it is difficult to imagine that eyes, though useless, could be in any way injurious
to animals living in darkness, I attribute their loss wholly to disuse. In one of the blind animals, namely, the cave-rat, the eyes are of immense size; and
Professor Silliman thought that it regained, after living some days in the light, some slight power of vision. In the same manner as in Madeira the wings
of some of the insects
have been enlarged, and the wings of others have been reduced by natural selection aided by use and disuse, so in the case of the cave-rat natural
selection seems to have struggled with the loss of light and to have increased the size of the eyes; whereas with all the other inhabitants of the caves,
disuse by itself seems to have done its work.
It is difficult to imagine conditions of life more similar than deep limestone caverns under a nearly similar climate; so that on the common view of the
blind animals having been separately created for the American and European caverns, close
similarity in their organisation and affinities might have been expected; but, as Schi?dte and others have remarked, this is not the case, and the
cave-insects of the two continents are not more closely allied than might have been anticipated from the general resemblance of the other inhabitants of
North America and Europe. On my view we must suppose that American animals, having ordinary powers of vision, slowly migrated by successive
generations from the outer world into the deeper and deeper recesses of the Kentucky caves, as did European animals into the caves of Europe. We
have some evidence of this gradation of habit; for, as Schi?dte remarks, 'animals not far remote from ordinary forms, prepare the transition from light to
darkness. Next follow those that are constructed for twilight; and, last of all, those destined for total darkness.' By the time that an animal had reached,
after numberless generations, the deepest recesses, disuse will on this view have more or less perfectly obliterated its eyes, and natural selection will
often have effected other changes, such as an increase in the length of the antennae or palpi, as a compensation for blindness. Notwithstanding such
modifications, we might expect still to see in the cave-animals of America, affinities to the other inhabitants of that continent, and in those of Europe, to
the inhabitants of the European continent. And this is the case with some of the American cave-animals, as I hear from Professor Dana; and some of
the European cave-insects are very closely allied to
those of the surrounding country. It would be most difficult to give any rational explanation of the affinities of the blind
cave-animals to the other inhabitants of the two continents on the ordinary view of their independent creation. That several of the inhabitants of the
caves of the Old and New Worlds should be closely related, we might expect from the well-known relationship of most of their other productions. Far
from feeling any surprise that some of the cave-animals should be very anomalous, as Agassiz has remarked in regard to the blind fish, the Amblyopsis,
and as is the case with the blind Proteus with reference to the reptiles of Europe, I am only surprised that more wrecks of ancient life have not been
preserved, owing to the less severe competition to which the inhabitants of these dark abodes will probably have been exposed.
-------------------------
Как можно видеть, у Дарвина мало сомнений в том, что у домашних животных упражнение укрепляет и увеличивает
определённые органы, а неупражнение приводит к их уменьшению и ослаблению, и что эти изменения наследуются. Первую главу,
на которую он ссылается, желающие могут перечитать сами:
http://www.literature.org/authors/darwin-charles/the-origin-of-species/chapter-01.html
Затем Дарвин задаётся вопросом, а не происходит ли чего-то подобного в дикой природе. Отмечая, что в последнем случае мы
лишены возможности проследить так же хорошо, как у домашних животных, степень развития признака у исходных форм, он тем не
менее приводит примеры структур, которые могут быть объяснены упражнением-неупражнением и наследованием приобретённых
таким образом признаков, часто в сочетании с естественным подбором, закрепляющим такие изменения, если они в определённом
смысле выгодны для их обладателей:
- крылья у птиц, утративших или утрачивающих способность к полёту (страусы и др.);
- крылья у ряда видов птиц на некоторых островах, где им не угрожали опасности, от которых нужно было спасаться при помощи
полёта, - и крылья у этих птиц почти исчезли;
- передние лапки некоторых видов навозных жуков, причём с разной степенью исчезновения;
- наблюдения над жуками на острове Мадера и др., в условиях сильных ветров, уносящих летающих насекомых в море показали
большое количество бескрылых видов и видов с недоразвитыми крыльями; в тех же случаях, когда насекомые в силу образа своего
питания всё-таки вынуждены летать, крылья у них больше и мощнее, чем у аналогичных форм на континенте, чтобы противостоять
действию ветра. Дарвин полагает, что упражнение-неупражнение могло в обоих случаях способствовать естественному подбору.
- глаза у некоторых видов грызунов, обитающих в грунте;
- наконец, глаза у видов-обитателей пещер. У одного из видов слепых животных, именно у пещерной крысы, глаза огромных
размеров (Дарвин объясняет это по аналогии с увеличенными крыльями жуков на Мадере); у всех остальных глаза редуцированы.
Дарвин отмечает, что
1) рассматриваемые пещерные животные принадлежат к совершенно разным группам (рыбы, крабы, насекомые, земноводные)
(т.е., добавлю от себя, эти изменения не могут быть объяснены сходной наследственностью),
2) в ряде случаев редукция глаз сопровождается увеличением и развитием органов осязания (антенны и проч.), и
3) условия жизни в пещерах очень стабильны (т.е., эти изменения строения тела не могут быть вызваны изменениями факторов
внешней среды).
2. Основные положения.
Дарвин предполагает, что если в силу своего образа жизни животное употребляет какие-то органы больше других, то они
укрепляются и увеличиваются в размерах, неупотребляемые же органы - уменьшаются. Если этот процесс происходит очень долго,
на протяжении многих поколений и результат такого упражнения-неупражнения закрепляется естественным подбором, то
результатом будет заметное изменение строения тела. В тех случаях, когда уменьшение органа нейтрально по отношению к
естественному отбору, т.е. не приносит не вреда ни пользы, оно может происходить как следствие своеобразного баланса в
организме.
3. Эксперименты.
Первое положение проверить очень легко. Напр., если человек занимается к.-л. видом спорта, у него лучше развиты
соответствующие мышцы. Дальнейшее, однако, на высших животных проверить нельзя из-за недостатка времени (большая
длительность смены поколений), а на людях - ещё и из-за этических соображений. Кроме того, для правильной постановки опыта
тут много неясного, в частности, сколько поколений требуется для конкретного вида, чтобы изменение стало заметным. А
результаты, полученные на растениях и низших организмах, можно интерпретировать по-разному из-за некоторых специфических
форм наследственности и изменчивости и связанных с этим проблем...
*** Стоит заикнуться о наследовании приобретённых признаков, сразу вешают ярлык лысенковщины. ***
Скорее всего, навешиватели ярлыков не читали ни Лысенко, ни Дарвина. Ума не приложу, что тут можно предпринять... Не
пробовали посоветовать им пойти в библиотеку? :-)
С уважением,
И.К.