Book IV chapter 10

The period of gestation¹ is, as a matter of fact, determined² generally in each animal in proportion to the length of its life. This we should expect, for it is reasonable that the development of the long-lived animals should take a longer time. Yet this is not the cause of it, but the periods only correspond accidentally for the most part; for though the larger and more perfect sanguinea do live a long time, yet the larger are not all longer-lived. Man lives a longer time than any animal of which we have any credible³ experience except the elephant, and yet the human kind is smaller than that of the bushy-tailed animals and many others. The real cause of long life in any animal is its being tempered in a manner resembling the environing air, along with certain other circumstances of its nature, of which we will speak later; but the cause of the time of gestation is the size of the offspring. For it is not easy for large masses to arrive at their perfection in a small time, whether they be animals or, one may say, anything else whatever. That is why horses and animals akin⁴ to them, though living a shorter time than man, yet carry their young longer; for the time in the former is a year, but in the latter ten months at the outside. For the same reason also the time is long in elephants; they carry their young two years on account of their excessive size.

We find, as we might expect, that in all animals the time of gestation and development and the length of life aims at being measured by naturally complete periods. By a natural period I mean, e.g. a day and night, a month, a year, and the greater times measured by these, and also the periods of the moon, that is to say, the full moon and her disappearance⁵ and the halves of the times between these, for it is by these that the moon’s orbit fits in with that of the sun [the month being a period common to both].

The moon is a first principle because of her connexion with the sun and her participation⁶ in his light, being as it were a second smaller sun, and therefore she contributes to all generation and development. For heat and cold varying within certain limits make things to come into being and after this to perish, and it is the motions of the sun and moon that fix the limit both of the beginning and of the end of these processes. Just as we see the sea and all bodies of water settling and changing according to the movement or rest of the winds, and the air and winds again according to the course of the sun and moon, so also the things which grow out of these or are in these must needs follow suit. For it is reasonable that the periods of the less important should follow those of the more important. For in a sense a wind, too, has a life and birth and death.

As for the revolutions of the sun and moon, they may perhaps depend on other principles. It is the aim, then, of Nature to measure the coming into being and the end of animals by the measure of these higher periods, but she does not bring this to pass accurately⁷ because matter cannot be easily brought under rule and because there are many principles which hinder generation and decay from being according to Nature, and often cause things to fall out contrary to Nature.

We have now spoken of the nourishment⁸ of animals within the mother and of their birth into the world, both of each kind separately and of all in common.

1 gestation   

n.怀孕；酝酿

参考例句：

• The gestation period can be anything between 95 and 150 days.妊娠期从95天至150天不等。
• This film was two years in gestation.这部电影酝酿了两年。

2 determined   

adj.坚定的；有决心的

参考例句：

• I have determined on going to Tibet after graduation.我已决定毕业后去西藏。
• He determined to view the rooms behind the office.他决定查看一下办公室后面的房间。

3 credible   

adj.可信任的，可靠的

参考例句：

• The news report is hardly credible.这则新闻报道令人难以置信。
• Is there a credible alternative to the nuclear deterrent?是否有可以取代核威慑力量的可靠办法？

4 akin   

adj.同族的，类似的

参考例句：

• She painted flowers and birds pictures akin to those of earlier feminine painters.她画一些同早期女画家类似的花鸟画。
• Listening to his life story is akin to reading a good adventure novel.听他的人生故事犹如阅读一本精彩的冒险小说。

5 disappearance   

n.消失，消散，失踪

参考例句：

• He was hard put to it to explain her disappearance.他难以说明她为什么不见了。
• Her disappearance gave rise to the wildest rumours.她失踪一事引起了各种流言蜚语。

6 participation   

n.参与，参加，分享

参考例句：

• Some of the magic tricks called for audience participation.有些魔术要求有观众的参与。
• The scheme aims to encourage increased participation in sporting activities.这个方案旨在鼓励大众更多地参与体育活动。

7 accurately   

adv.准确地，精确地

参考例句：

• It is hard to hit the ball accurately.准确地击中球很难。
• Now scientists can forecast the weather accurately.现在科学家们能准确地预报天气。

8 nourishment   

n.食物，营养品；营养情况

参考例句：

• Lack of proper nourishment reduces their power to resist disease.营养不良降低了他们抵抗疾病的能力。
• He ventured that plants draw part of their nourishment from the air.他大胆提出植物从空气中吸收部分养分的观点。