The Ten Descents

The Purāṇic ten. The canonical list is late and the tradition knows it: the Bhāgavata counts twenty-two descents and then says they are innumerable, “like rivulets flowing from inexhaustible sources of water.”^[5] But by the time of the Padma, Garuḍa and Matsya Purāṇas the ten had settled into a formula — matsyaḥ kūrmo varāhaś ca nṛsiṃho vāmanas tathā, rāmo rāmaś ca kṛṣṇaś ca buddhaḥ kalkī tataḥ smṛtaḥ: fish, tortoise, boar, man-lion, dwarf, the two Rāmas, Kṛṣṇa, Buddha, Kalki.^[1,2,3,4] Kṣemendra wrote his Daśāvatāracarita on that list in 1066; Jayadeva sang it a century later in the hymn Odissi dancers still perform — though his eighth is Balarāma and Kṛṣṇa is the one being addressed, and the Śrī Vaiṣṇava lists of Vedānta Deśika drop the Buddha altogether.^[6,7,8] I use the Padma formula, the one most of the world means by “the ten,” and note the Balarāma variant where it matters.

The Āyurvedic ten. Caraka's Śārīrasthāna 4, Suśruta's Śārīrasthāna 3 and Vāgbhaṭa's Śārīrasthāna 1 all walk the womb month by month, and — this is the first honest thing to say — they disagree. Caraka's first month is a kheṭabhūta, a “jelly-like mass”; Suśruta's and Vāgbhaṭa's is kalala. Suśruta lets the heart manifest in the fourth month and with it the sentient principle, so that the fetus begins to want things and the mother becomes dauhṛdinī, two-hearted; Caraka's fourth month is merely sthiratva, stability, and he starts the two-hearted state a month earlier, with the senses; Vāgbhaṭa moves consciousness to the fifth month and never uses the word dauhṛda at all, speaking instead of the mother's śraddhā, her cravings, which it is “not desirable to disregard” because the fetus's heart “is born of the mother, and … is connected with the mother's heart.”^[27,28,29] Suśruta gives the fifth month to manas and the sixth to buddhi; Caraka gives them to flesh-and-blood and to strength-and-complexion; Vāgbhaṭa's sixth is a list — “snāyu (ligaments/sinews), sirā (veins), hair, strength, complexion, nails, and skin.”^[27,28,29] They converge again only at the seventh month, which all three call complete, and at the eighth, whose unsteady ojas all three fear. The Bhāgavata's own chapter and the little Garbha Upaniṣad add two more month-lists, both different again.^[30,31] A tradition that agreed on everything would be less interesting; one that disagrees about consciousness and agrees about the seventh month is telling us something, and we will come back to what.

The Jyotiṣa ten. Varāhamihira, in the chapter of the Bṛhat Jātaka on conception, gives the ten months in a single verse: seven stage-names — kalala, ghana, aṅkura, asthi, carma, aṅgaja, cetanatā: jelly, mass, sprout, bone, skin, hair, consciousness — and ten lords: Venus, Mars, Jupiter, the Sun, the Moon, Saturn, Mercury, then the lord of the conception-ascendant, then the Moon and the Sun again.^[34] The commentators supplied the missing three stages (the child feeds through the cord; it is filled with cares; it is born) and the rule that a month whose lord is afflicted at conception is a month of danger.^[34] Two of these lords, we will see, match the Āyurvedic stage of their month with a precision that looks deliberate.

The embryologist's forty weeks. Obstetrics counts from the first day of the last menstrual period, so that a pregnancy is 280 days, forty weeks — which is to say, exactly ten lunar months of twenty-eight days.^[58] The arithmetic is the reason the instrument below can exist: month n of the tradition is weeks 4(n−1) to 4n of the chart, with conception falling in the second week. (Embryologists proper count from fertilization, two weeks less; I convert throughout and say so.^[36]) The forty weeks divide into an embryonic period, the first eight after fertilization, in which the body plan is laid down and the creature looks least like a person, and a fetal period of growth and maturation.^[36,37]

Four ladders, then, each of ten rungs. Figure 1 lays them out on one time-line; the instrument in the next section lets you climb them.

When the gods and the demons churn the ocean of milk, the mountain they use for a churning-rod begins to sink, and Viṣṇu becomes a tortoise and dives beneath it, so that the whole rotation turns on his back.^[12] The tortoise is older than Viṣṇu's descents: in the Śatapatha Brāhmaṇa it is Prajāpati himself, who “made” the creatures and is therefore called kūrma, and whose shell is at once the earth, the sky, and the space between; “this tortoise,” the text adds, “is the same as yonder sun.”^[11] What the second descent supplies is not motion but steadiness — an axis held still under an immense turning. Every other treasure comes out of the churning; the tortoise is what lets the churning happen.

The second month in the texts is ghana: the jelly becomes dense. Caraka says the mass hardens into a knot, a tendon or an egg, and reads the sex from the shape; Suśruta gives the physics — the great elements, “cooked by cold, heat and wind,” condense; Vāgbhaṭa follows him: “from the kalala, it becomes a dense mass (ghana), a fleshy mass (peśī), or a tumor-like mass (arbuda). From these, in order, come males, females, and eunuchs.”^[27,28,29] The Bhāgavata's count reaches the head at one month and the arms and legs at two; the Garbha Upaniṣad puts the head at two months.^[30,31] Varāhamihira names the month ghana and gives it to Mars, the planet that in his scheme rules the marrow — a heat-and-blood planet for the month Suśruta says is cooked.^[34,35]

The embryologist's second month is the one on which the whole of comparative anatomy turns, and it goes fast. Sixteen days after fertilization the notochord forms, a stiff rod down the midline that is the axis around which the vertebrate body is built. Neural folds rise beside it and close into a tube; on the twenty-second day, at Carnegie stage 10, the heart — still a tube — begins to beat.^[36,38,39] Over the next ten days the embryo develops the features every vertebrate embryo develops: a row of somites down the back, four pharyngeal arches at the neck with clefts between them that look, and only look, like gill slits; paddle-shaped limb buds; a tail that reaches its greatest length around the thirty-eighth day and then, over the following week, is resorbed.^[38,40] The heartbeat can be seen on a transvaginal scan from about the sixth week of the chart.^[44] The first blood cells, made in islands on the yolk sac, are in circulation by the fourth week, and before the month ends the liver has begun to take over their manufacture — the first of three hand-overs, yolk sac to liver to marrow, that the blood makes before birth.^[41] By the end of the month, forty-two days after fertilization, the hand-plate shows digital rays, and the first movements can be seen on ultrasound.^[39,45]

This is also the window that the modern successor to Haeckel's law singles out. The hourglass model — to which section XIII returns — holds that vertebrate embryos are most alike not at the start of development but in the middle, at a “phylotypic period” of organogenesis; in the mouse that period is embryonic days 9.5 to 10.5, which the stage tables map onto human Carnegie stages 10 to 13, days 22 to 32 after fertilization.^[39,64] The waist of the hourglass, in other words, falls in the traditional second month — the month of the tortoise.

Text Order Image The density is textual. The position is structural, and it is the most important structural fact in this essay: the one stretch of development in which a human embryo really does resemble the embryos of fish, turtle and chick — the only stretch in which the old slogan retains any truth — is the second month, and the second descent is the animal that holds the axis still while everything turns. The notochord as Mandara and the first heartbeat as the churning are my images; I offer them as such. But the tortoise sitting exactly at the waist of the hourglass is not something I arranged.

Set the clock to month 2 →

Hiraṇyakaśipu has made himself unkillable by a boon of exclusions: not by any created being, not by man or beast, not indoors or outdoors, not by day or night, not on the ground or in the sky, not by any weapon.^[15] Viṣṇu's fourth descent is the answer to a riddle. Out of a pillar, at his devotee's word, bursts a form “neither that of a man nor that of a lion,” who takes the demon on his lap in a doorway and opens him with his nails.^[15] (The twilight hour that makes it neither day nor night is the commentators' addition; the verses give the doorway, the lap and the nails.^[15]) Narasiṃha is the avatāra of the threshold: a being defined by being two things at once, in the place between.

The fourth month is the month the texts disagree about most, and the disagreement is about exactly this: when does the thing inside become a someone? Suśruta is unambiguous. In the fourth month the limbs are distinct and the heart becomes manifest, and because the heart is the seat of the cetanā-dhātu, the sentient principle, consciousness appears with it; the fetus now “expresses its desire for things of taste, smell and so on” through its mother's cravings, and the woman with two hearts in her is called dauhṛdinī, whose wishes must be honoured lest the child be born crooked, lame or blind.^[28] Caraka says only that the fetus becomes stable and the mother heavy; Vāgbhaṭa, that “the limbs become distinct” — and, a few verses earlier, that the fetus's heart “is born of the mother, and … is connected with the mother's heart. Therefore, it is not desirable to disregard the cravings of a pregnant woman.”^[27,29] The Bhāgavata gives the month the seven dhātus; Varāhamihira names it asthi, bone, and gives it to the Sun — the planet that, in his own second chapter, rules bone.^[30,34,35]

The embryologist's fourth month, weeks twelve to sixteen of the chart, is the month in which the fetus becomes unmistakably human and, at the same time, furred like an animal. The skeleton is now widely ossified and shows on ultrasound; sex can be told on the scan with ninety-six percent accuracy at thirteen weeks; the male external genitalia are complete by the month's end.^[38,43] And at about three months after fertilization the skin sprouts lanugo — a fine, downy hair that will spread from the head down over the whole body by the fifth month and be shed again before birth, a coat that no adult human wears and every fetus does.^[38] A mother carrying her second child may feel the first flutter of movement in these weeks.^[38]

Text Order Image Bone is textual twice over in the Jyotiṣa — the stage is asthi and the lord is the Sun, who rules asthi — and the manifest heart is Suśruta's. The threshold is structural: the fourth month opens the second trimester, the passage from the perilous first months to the settled middle ones, and Caraka's word for it is sthiratva. The rest is image, but I think it is a good one. A being neither wholly inside its mother nor separate from her, its heart joined to hers so that its desires speak in her mouth; a face that has just become human on a body wearing a lion's coat: if you wanted an icon for the fourth month, the man-lion on the threshold with a child on his lap would do.

Set the clock to month 4 →

Rāma of the Axe is the descent that cuts. At his father's command the boy beheads his own mother, then asks as his boon that she live again, and she rises “as if from sleep”; later, with the axe that gives him his name, he clears the earth of its warrior caste twenty-one times; and he is one of the deathless — the Bhāgavata says he lives still, calm, weapons laid down, on Mount Mahendra.^[18] The sixth descent is violence in the service of restoration, and a being who cannot die.

The sixth month in the texts is hair, sinew and intellect. Varāhamihira names it aṅgaja, which his translator glosses as hair, and gives it to Saturn — who in the second chapter rules the sinews and is himself described as “hard-haired.”^[34,35] Vāgbhaṭa's sixth month begins with sinews and hair — “snāyu (ligaments/sinews), sirā (veins), hair” — and continues through “strength, complexion, nails, and skin”; Caraka's is strength and complexion; Suśruta's is buddhi, the intellect, arriving a month after the mind.^[27,28,29] The Garbha Upaniṣad gives the sixth month the mouth, nose, eyes and ears.^[31]

The embryologist's sixth month, weeks twenty to twenty-four, is the month of viability and of the cortex. Eyebrows and eyelashes appear, and the fused eyelids begin to part.^[39,48] The brain's smooth surface begins to fold — the Sylvian fissure at twenty-two weeks, the central sulcus at twenty-four — and axons from the thalamus begin to enter the cortical plate.^[49,50] Behind that folding is a cull: the developing nervous system makes far more neurons than it keeps, and in many neuronal populations between a fifth and four-fifths, often about half, die on schedule in the weeks that follow.^[52] The lungs' type II cells begin to make surfactant at twenty-four weeks; the cochlea becomes functional.^[38,46] And at twenty-two to twenty-four weeks a fetus becomes able, sometimes, to live outside its mother: in the American cohort of 2013–2018, eleven percent survived birth at twenty-two weeks, forty-nine at twenty-three, seventy at twenty-four.^[54]

Text Order Image Hair and sinew are textual across three authors, and Saturn-for-sinew is the second of Varāhamihira's deliberate-looking matches. Viability at the sixth month is structural — the textbooks put it here, and nowhere else. The axe is image, twice over: the pruning of a brain that keeps only what it needs, and the cut that could now, for the first time, be survived. The sixth-month fetus is the first that could live severed from its source. That is what a cirañjīvin is.

Set the clock to month 6 →

Kṛṣṇa is the eighth descent and he was the eighth child. A voice from the sky tells Kaṃsa that the eighth child of the woman in his chariot will kill him; he imprisons her and kills her infants one by one — six of them — and the seventh is spirited from her womb into another woman's; and the eighth is born at midnight in a prison, the guards asleep and the doors open, and carried across the Yamunā before dawn to be raised as a cowherd's son and steal butter.^[20] His birthday is the eighth of the dark fortnight; the vow bears the number in its name, Janmāṣṭamī.^[26] Of the ten, he is the only one whose story is a story of a dangerous gestation.

The eighth month is the month the Āyurvedic texts fear. All three say the same strange thing: ojas, the vital essence, passes back and forth between mother and child — “again and again,” Caraka says, through the channels that carry nourishment; “repeatedly,” says Vāgbhaṭa, so that “they both become emaciated and elated” — and because the ojas is unsteady, a child born now is at risk.^[27,28,29] Caraka calls the birth merely vyāpattimat, hazardous, and the month agaṇya, “not to be counted on”; Suśruta and Vāgbhaṭa say flatly that “a child born then does not survive,” and Suśruta prescribes an offering of meat to the demons who take it.^[27,28,29] Greek medicine held the same belief, and Reiss and Ash traced it from a Hippocratic treatise on the eighth-month child through the Talmud to their own obstetric patients in the 1980s — a superstition, they called it, but one that two ancient medical traditions arrived at independently.^[33] Varāhamihira's eighth month is the only one whose lord is not a planet but the lord of the conception-ascendant — the native's own — as if the chart's self had to stand guard.^[34]

The embryologist's eighth month, weeks twenty-eight to thirty-two, is the month of butter. The fetus weighs about a kilogram at twenty-eight weeks and will gain two and a half more by term, most of it in the last ten weeks and much of it fat: the newborn is twelve to sixteen percent fat, and nearly all of that is laid down from now on.^[55] The lungs' surfactant becomes sufficient to keep them open by thirty-two weeks.^[38] The pupils begin to respond to light; active and quiet sleep become recognizable; the mother's antibodies, crossing the placenta, reach about half her own level.^[48,53,56]

Text Order Image That the eighth month is perilous is textual in three Āyurvedic authors and, independently, in Hippocrates; that the eighth descent was himself the eighth child, hunted in the womb, is textual in the Bhāgavata. Whether the ancient fear had a basis is another question — eight-month babies do very well today, and there is no reason to think they fared worse than seven-month babies then, whatever the physicians wrote — but the position of the fear on both ladders is the same. The butter is mine. Yet the eighth month is the month in which the child begins to store its fat, and the picture of an ojas that is stolen back and forth between two hearts, by a child who will grow up to be the thief of butter, is one I could not leave out.

Set the clock to month 8 →

Kalki has not come. The Bhāgavata says he will: at the close of the Kali age, when kings have become thieves and bodies have grown small, in the house of a brāhmaṇa named Viṣṇuyaśas in the village of Śambhala, mounted on the swift horse Devadatta, with a sword, to end the age and begin a new one.^[22] He is the only descent whose story is entirely in the future tense, and the only one whose work is not to save something within the world but to end the world's present cycle so that another can start.

The tenth month is birth, and here every text is unanimous and a little afraid. Caraka: past the eighth month even by a day, from the ninth to the tenth is the time of delivery, and longer is abnormal; Suśruta: born in the ninth, tenth, eleventh or twelfth month, otherwise something is wrong; Vāgbhaṭa: “even if one day has passed in that eighth month, thereafter is the time for delivery,” and “after a year, if retained in the womb by vāta, it causes disorders.”^[27,28,29] The Bhāgavata describes the mechanism: the ten-month child, still praising, is seized by the birth-wind and thrust out head-first, breathless, “its memory struck away,” and falls to the ground and cries.^[30] The Garbha Upaniṣad has the same forgetting and gives the wind a name: “at the door of the womb, pressed as by a machine, born in great pain, it is touched by the vaiṣṇava wind, and then it does not remember its births and deaths.”^[31] Both modern translators render vaiṣṇava as “all-pervading”; the word is also, plainly, “Viṣṇu's.” The last of Viṣṇu's descents, in this text, is the breath that makes us forget the others. Varāhamihira gives the month to the Sun, the soul of the Cosmic Man — the month of coming into light.^[34,35]

The embryologist's tenth month is term. Thirty-seven weeks is “early term,” thirty-nine “full term,” and forty is the two hundred and eightieth day from the last period — ten months of the moon exactly.^[58] A fetus of thirty-eight weeks hears its mother's voice through her body and its heart quickens; to a stranger's voice it slows.^[47] Then the wind: labour, the passage, the cord cut, and the first breath, which the newborn draws itself. What the Ṛgveda prayed for three thousand years ago is what the delivery room still prays for — niraitu jīvo akṣato, may it come forth alive, unharmed.^[32]

Text Order Image The end of an age is textual: Kalki ends the Kali-yuga, and birth ends the womb; the ten-month count is Vedic, Purāṇic and obstetric alike. The sword as the knife on the cord is my image, and so is this: that each newborn is Kalki, the descent still to be lived, arriving with its memory struck away into an age that is only beginning. Vāgbhaṭa's chapter is called the descent into the womb; the tenth descent is the descent out of it.

Set the clock to month 10 →

In 1866 Ernst Haeckel, Darwin's most zealous apostle in Germany, wrote the sentence that would outlive everything else he wrote: Die Ontogenesis ist die kurze und schnelle Recapitulation der Phylogenesis — the development of the individual is a short and rapid recapitulation of the development of the lineage.^[59] He meant it literally. The human embryo, he held, climbs through the adult forms of its ancestors: a fish stage with gills, a reptile stage, a mammal stage, and only at the end a human one; the “biogenetic law” was that evolution works by adding new stages onto the end of the old sequence. Two years later, in his Natural History of Creation, he published the first comparative embryo plates, and in 1874 the grid that made the law famous — fish, salamander, turtle, chick, pig, calf, rabbit and human in columns, all but indistinguishable in the top row and diverging only lower down — and was accused, by Ludwig Rütimeyer in 1868 and by the anatomist Wilhelm His in 1874, of having drawn what he wished to see. One woodblock in the 1868 book had been printed three times and labelled dog, chick and turtle.^[59,62]

The drawings were re-examined in 1997 by Michael Richardson and colleagues, who photographed real embryos at the stage Haeckel had drawn and found them varying more than tenfold in size and considerably in form: “there is no highly conserved embryonic stage in the vertebrates,” their title said, and Haeckel's figures depicted “a stylised amniote embryo.”^[61] Nick Hopwood's history of the affair, the fairest account, concludes that the drawings were idealized type-figures synthesized from several sources — “unconventional, reckless even, but there was no intent to deceive.”^[62] The strong law, in any case, had died long before the drawings were retried. Walter Garstang showed in 1922 that embryos do not pass through adult ancestral forms at all; Stephen Jay Gould's Ontogeny and Phylogeny (1977) gave the whole history its standard obituary.^[63]

What was true in Haeckel had been said better forty years before him, by Karl Ernst von Baer, who was not an evolutionist and whose four laws of 1828 remain the sanest thing in the subject. The general features of a large group appear in the embryo before the special ones; from the general the less general develop; the embryo of a given form, instead of passing through other forms, diverges from them; and therefore — the fourth law — “the embryo of a higher form never resembles any other form, but only its embryo.”^[60] A human embryo at five weeks does not look like a fish. It looks like a fish embryo. The pharyngeal arches are not gills that became a jaw and a larynx; they are the shared embryonic scaffold from which gills are built in a fish and a jaw and a larynx in us. The tail is not a monkey's tail; it is the vertebrate tail-bud, which in us is resorbed. The kidneys that form first and regress are the ones a fish keeps — the pronephros of its larva, the mesonephros of its adult. Ancestral embryonic features are conserved because later steps depend on them; ancestral adult features are not recapitulated at all.^[38,60]

And in the last thirty years a second correction has arrived from the study of genes. Vertebrate embryos, it turns out, are not most alike at the beginning, as both Haeckel and von Baer supposed. Eggs, cleavage and gastrulation differ wildly between a fish, a frog and a mouse — yolk, implantation, the whole logistics of the first days are species business. The likeness peaks in the middle, at a “phylotypic period” of organogenesis when the body plan is being laid out, and diverges again afterward. Denis Duboule proposed the shape in 1994, Rudolf Raff drew it as an hourglass in 1996, and in 2010 and 2011 three laboratories measured it directly in the expression of genes across development in flies, in zebrafish, and across four vertebrates: the transcriptomes are most conserved at the waist.^[64] In the mouse the waist is embryonic day 9.5 to 10.5. No one has staged it in the human embryo directly, and I will be careful to say that the placement in Figure 13 is an inference through the standard stage tables; but those tables put the mouse's waist at Carnegie stages 10 to 13 — days 22 to 32 after fertilization, weeks five to seven of the chart, the heart of the traditional second month.^[39,64]

So this is what survives of the slogan, in three sentences. Embryos resemble the embryos of their relatives, not the adults of their ancestors. The resemblance is greatest not at the start but at a waist in the second month, when the axis, the heart, the arches and the buds are being laid down. And single characters — the arches, the tail, the transient kidneys, the fur the fetus grows and sheds — do carry the history of the lineage, one feature at a time, without the whole organism ever replaying it.^[61,64] Ontogeny does not recapitulate phylogeny. It recapitulates the embryology of phylogeny, briefly, in the month of the tortoise.