בבא קמ נה,א
אמר שמואל אווז ואווז הבר כלאים זה בזה ... מאי טעמא ? אמר אביי זה ביציו מבחוץ וזה ביציו מבפנים
Shmuel said "a domestic goose and a wild goose are kilayim with one another"...what is the reason [to classify them as two distinct species]? Abbaye explained, the male wild goose has testicles that are external, but the male domestic goose has testicles that are internal...(Bava Kama 55a)
The Koren Talmud on Wild and Domestic Geese
In today's Daf Yomi page of Talmud, we enter a brief discussion of the biblical prohibition of כלאים - kilayim - which is the prohibition of cross breeding two different species, be they plant or animal. According to the great talmudic sage Abbaye (died c. 339 CE), cross breeding a domestic goose and a wild goose is forbidden as well, because they seem to be two different species as evidenced by their anatomy: "the male wild goose has testicles that are external, but the male domestic goose has testicles that are internal." Here is the background note found in The Koren Talmud.
Today, these two types of birds are treated as one species. The wild goose is classified as the Anser anser, also known as the greylag goose, and the domestic goose is classifeid as the Anser anser domestica. Although the differences between them are not always apparent, they do differ in several ways, such as in their appearance, voice, and behavior. In terms of their appearance, they differ in color, as the wild goose is usually gray and the domestic goose white, and the neck of the domestic goose is shorter than that of the wild goose.
Another difference is that the male organ of the wild goose is more recognizable than that of the domestic goose. As for laying eggs, the wild goose lays fewer eggs than the domestic goose, which can lay more than ten eggs at a time.
All of this is very helpful indeed, but it does not address the claim that was made by Abbaye and which Rashi clarifies: "ביצי הזכרות ניכרין באווז הבר מבחוץ" - that the testes of wild geese may be seen outside of the body. Is that the case? Let's see what the geese experts have to say.
The Handbook of Bird Biology
Here are the ornithologists at the Cornell Lab of Ornithology on the location of bird testes:
Oval or elliptical in shape, avian testes are paired and lie within the body cavity at anterior end of each kidney.
In most birds the the intestinal, urinary, and generative canals open into a cavity called the cloaca. However the Cornell Handbook notes that a few species including ostriches, ducks and geese, have a more advanced copulatory organ, the cloacal phallus. "Although often called a 'penis', this structure differs from the mammalian equivalent: since it lacks an internal urethra, sperm must travel along the external surface of the phallus." Good to know.
The Manual of Ornithology: Avian Structure and Function
The authors of the 1993 Manual of Ornithology are an interesting duo: on is a professor of biology, and the other, a radiologist. Here is their description of where bird testes are located:
Male birds have paired testes within the abdominal cavity just anterior and ventral to the lobes of the kidneys. During much of the year the testes may be difficult or impossible to find because of their small size, but during the breeding season the testes may grow to several hundred times their non-breeding size, resembling two bean-shaped organs lying next to the kidneys on the dorsal abdominal wall...Some birds experience a nightly drop in body temperature that allows sperm development in males. In other species the male develops a cloacal protuberance, a swelling of the terminal end of the vas deferens. This functions like a mammalian scrotum, holding the developing sperm away from the high temperatures within the abdomen.
To be clear: there are no testes on the outside of the body, as Abbaye claims; the closest we get to this is a small swelling during the mating season.
The last reference book we will look at is Goose Production, published in 2002 by Food and Agriculture Organization of the United Nations. Chapter Five addresses the male (and female) reproductive system found in geese:
There are two bean-shaped testicles inside the body cavity which produce both spermatozoa and male hormones. They are highly vascularized and change in size and position according to whether the gander is sexually active or not...the copulatory organ of the gander is very well developed. It is invaginated, spiral-like, and is about 15cm in length.
To recap: Geese testes are only located within the body cavity. No birds - geese included - have a scrotum, though sometimes the cloaca may swell to hold the maturing sperm. And of course there is no difference between the natural and wild goose in any of these anatomical facts.
So what Did Abbaye mean?
What then, are we to make of Abbaye's testicular error? A couple of options spring to mind:
- The translation of אווז - avaz - as a goose is wrong, and he was referring to another species. The problem with this is (1) there is no dispute as to the translation and identification of this word and (2) even if Abbaye was referring to another species of bird, in no species do the testes reside in any place other than snugly inside the abdomen.
- The geese in Abbaye's time were different. There is no way to determine if this claim is true, though based on what we know about evolution it would be a pretty remarkable evolutionary change in the space of less than two millennia. Wait a minute, you say: what about the article two days ago in The New York Times with the title 'Evolution Is Happening Faster Than We
Thought'? Perhaps two millennia is enough time for a change like this to occur? Well, it is true that certain evolutionary changes may happen more quickly than scientists had previously expected, but this only happens "as long as natural selection — the relative benefit that a particular characteristic bestows on its bearer - is strong." One place where this happens is within our cities, where, for example, the temperature can be much higher or the ambient light much brighter, than in the surrounding countryside. However no such selective pressure is known to have occurred for geese living betwen Abbaye's time and our own. Absent this evolutionary pressure, the suggestion that the internal anatomy of geese has changed is without any merit.
- Abbaye was wrong. Abbaye was descended from a family of priests, and after the death of his parents was raised by an uncle and a kindly foster mother. As a young man Abbaye spent some time in poverty: he worked at night irrigating agricultural canals so that he could be free during the day for study. Eventually his fortune changed and he became a wine trader and a farmer with tenants of his own. But there is no record of his having worked closely with animals, and animal husbandry would be an unlikely occupation for the head of the rabbinic academy in Pumbedita, a position that he occupied for the last five years of his life. It is very likely then, that wise as he was, Abbaye simply had no factual experience on which to base his claim that wild and domesticated geese have different male sexual organs. It is always best to speak with authority only about that which you are certain is correct. Abbaye was certainly in authority as a great leader of a great rabbinic academy. But being in authority, and being an authority are by no means the same. That's a great lesson to remember.