Rabbinic Philosophies and the Scientific Method

Last time on Talmudology

Although permitted by Jewish law, in Victorian Britain it was illegal for a man to marry his dead wife’s sister – though many did.  There were attempts to change the law and permit this kind of marriage, but many in the Church of England remained opposed. Writing in 1887 in The British Medical Journal, an anonymous surgeon claimed that science could provide support for the permissive movement. But we now know that the science he offered (that all future children of a woman, regardless of the father, carry the traits of the man who first impregnated her) is nonsense. This shows that science changes. But if science changes, what should we do when it seems to challenge Jewish tradition? 

What is stuff made of?

This week I had the pleasure of studying science with my 13-year-old daughter Ayelet. She was preparing for a test, and the subject was “Atomic Structure”.  Here is some of the content she shared with me: (Read it through - it's really not scary.)

(All slides courtesy of Berman Hebrew Academy, 8th Grade Science Class)

So to sum it up, Ayelet taught me that in addition to the model of Aristotle, we've had at least five explanations of what stuff is made of:

why don't kids reject science?

Now here is a fascinating thing. My daughter had no existential breakdown when she realized that the way scientists understand the world changes over time. She did not once say to me “Scientists are useless. They change their minds all the time. They must have no idea what they are talking about. I’m done with learning science…” Not even close (though, by the end, she was most certainly done with studying for her science test). Let's compare this attitude towards the changing nature of scientific knowledge with that of some Jewish thinkers, past and present.  

reuven landau & foucault's pendulum

Let’s start with someone who is not well known (unless you read the book).  Revuen Landau (d. 1883?) wrote strongly against the Copernican model of the solar system in which the sun is stationary and the earth revolves around it.  But in 1851 Foucault demonstrated with his pendulum that the earth really was revolving, (though it didn’t prove that it revolved around the sun). What to do with this evidence? Landau had no doubt. Science was fickle and changed all the time, so don’t worry about it.

Although the astronomers of our time pride themselves on finding a compelling demonstration that the earth moves by using the pendulum, you should dismiss this too. For it has happened many times that an earlier scientist proved a point beyond a doubt using an unequivocal demonstration, and yet a later one came and disproved that which was established earlier, including the [previously] convincing demonstrations, and showed a new explanation for the findings...

This skepticism about accepting the results of the famous pendulum experiment reflected Landau's attitude towards science in general, which can be best summed up like this. Since all scientific theories are in a state of constant flux, it's best not to pay too much attention to them. When Jewish beliefs are challenged by science, take the long view; in doing so, tradition will ultimately be vindicated. (His view was actually more nuanced than that, insofar as he was willing to quote from the science when it supported his anti-Copernican position, but criticized the same science as being fickle when it proved to be problematic.) 

Rav Kook 

Abraham Isaac Kook (1865–1935), the first chief rabbi of Palestine, is thought to have welcomed science as a tool to understudying God's universe. While this is generally correct, (he was famously sympathetic to Darwin's theory, though in none of his writings does he mention Darwin by name,) Rav Kook cautioned against accepting  all scientific theories "...even those about which there is general agreement, for they are like a fading flower (כי הן כציץ נובל). Soon enough new instruments will be developed, and people will mock these new theories . . . only the word of our God will last forever." Because scientific theories come and go so quickly, Rav Kook felt it was best not to get too attached to them.

The Ben Ish Hai

Joseph Hayyim (1834–1909) was born in Baghdad, where at the age of twenty-five, he succeeded his father as leader of the Jewish community. He authored a work that is widely read by Sephardic Jews to this day called Ben Ish Hai, but it was in another work that he advanced an example of extreme rabbinic skepticism towards science.

Even when [a scientific idea seems] persuasive, it is likely to be rejected and overturned, because later enlightened people will come to understand something that arises from the natural world that had not been understood by those earlier. [These earlier people] had invented their own system based on their understanding. When an objection to an earlier system arises, the entire system is destroyed, because when a foundation is destroyed the whole house crumbles...Over the last two thousand years a number of systems have been developed and overridden in the fields of natural sciences and astronomy. One builds and another destroys, like the building of [the Egyptian cities of] Pitom and Ramses. 

Note the language the Ben Ish Hai uses here.

“When an objection to an earlier system arises, the entire system is destroyed, because when a foundation is destroyed the whole house crumbles.”

But is this a fair description of the scientific method? Did Bohr's atomic model (work for which he won the Nobel prize in 1922) really destroy the entire edifice of physics, or did it nudge it closer to the truth? 

Pinhas hurwitz & Sefer Haberit

Sefer Haberit is probably the best selling Jewish book of science ever written. First published anonymously in 1797, it remains in print to this day.  Its author, Pinhas Hurwitz from Vilna, wrote the book in two parts; the first was a scientific encyclopedia dealing with what he called human wisdom, and the second part dealt with divine wisdom, (and was ostensibly focussed on explaining a sixteenth century kabbalistic work by Hayyim Vital).  

Hurwitz cautioned against ever accepting any particular scientific theory.  His notion of the way science changes is certainly not as extreme as that of the Ben Ish Hai, but it placed him in a rather odd situation. Hurwitz didn't much like the new Copernican model of the universe with the earth revolving around the sun, but neither could he go back to the old geocentric model. So in the spirit of compromise he suggested following the model proposed by Tycho Brahe some two centuries earlier, the details of which need not detain us.  But Hurwitz knew that this model had been utterly discredited in the scientific community. No problem, wrote Hurwitz, because science is always changing its mind.  Perhaps one day this old discredited model will come back into favor, and when it does, it will pose less of a problem for traditional Jewish belief than the current widely accepted Copernican model.

. . . who knows if at a later time or in one of the many future generations that will come after ours, [Tycho's discredited] theory may be accepted. Then it may become permanently accepted, for this is the way among the Gentiles that some opinions have their moment. At times they are rejected and at other times they are accepted. Even if a theory is rejected from its very inception . . . eventually there may arise a person who adopts the theory and succeeds in spreading it across the entire world...  

So according to Hurwitz, it made sense to accept a discredited theory that supported his notion of Jewish belief, because one day, perhaps, the scientists will go back to believing what they now reject as false.  It is as if today, we claimed that it's perfectly reasonable to believe the world is flat, because that was once an accepted belief, and who knows, perhaps one day scientists will return to the flat-earth theory and believe once again that it is a true description of the world.

The Maharal of Prague

Another Jewish skeptic of science is the great Rabbi Judah Loew (d.1609), known by his acronym Maharal. In a long essay he contrasted knowledge attained from observation of the universe and knowledge obtained from Jewish tradition.  The former is constantly changing, and inferior to the unchanging wisdom received through divine revelation.

 ... the [Gentile] nations want nothing more than to become wise through this knowledge, and indeed they became expert in this field of knowledge, as all know. Yet there always came other experts afterwards who overturned the knowledge that they had worked so hard to attain...However the Sages of Israel who received their information from Moses at Sinai—and who himself received this from God—are the only ones who alone possess the Truth...

Note that the Maharal made an expansive claim (and one that was very popular circa 1580): all true knowledge comes from religion  - or more precisely - from the rabbis. He did not say that the rabbis provided spiritual insights while "experts" (who we'd call "scientists" today) provided insights into the physical universe. Rather he claimed that truth can only come from the "Sages of Israel who received their information from Moses at Sinai".  As a consequence, scientists really have no seat at the table when we discuss knowledge.  

rabbi moshe meiselman

The last example we will look at is a contemporary figure, Rabbi Moshe Meiselman. His recent book states that he "was trained by some of the great names in mathematics, philosophy and the sciences at two of America's premier universities." Great! Rabbi Meiselman has studied outside of the walls of the Jewish ghetto - something the Maharal could not do, even if he had wanted.  So we should expect a fresh and sophisticated approach from a rabbi who gets science, right? Wrong.

Science has no sacred cows. Over the past hundred years, scientific theories have changed with unprecedented rapidity. Whoever weds his belief system to any particular scientific theory will soon find that system outdated and will be forced to look for a new one... (585)

Rabbi Meiselman here has the same old understanding of science as the Ben Ish Hai. When a new scientific theory replaces an older one, everything comes crashing down and we are left wandering in search of something new to grab on to. Elsewhere though, he sounds more like the Maharal, who objected to scientific hubris, and reminded us that science can make no truth claims, for these are reserved for the rabbis.

[A]t every juncture, just as soon as the dust of the latest revolution has settled, one inevitably finds scientists claiming that the ultimate secrets often universe have finally been unlocked and that there are few surprises left in store...Absolute truth has been attained! (584)

Now in fairness to Rabbi Meisleman, elsewhere in his long book he shows a better understanding of the  scientific method.

Science, when properly understood, lays no claim to the knowledge of truth. It embodies the search for theories that approach the truth. It inches in the direction of truth, but it never claims to be in possession of that precious commodity. (579)

Which is it then, Rabbi Meiselman? Do scientists claim to have attained the Truth (as he writes), or rather are they engaged in a process that brings us ever closer to this goal without their having arrived (as he also writes)? His is a a peculiar mix of positions. (You can read other critiques of Rabbi Meiselman's book here and here.)

Got a spare five minutes? Great, then we can go a little deeper, and see why these rabbinic philosophies don't really reflect what science is all about. To do that, let's consider the truth claims of the following pairs of scientific statements. 

1. The earth is flat vs The earth is round.

Both of these statements are incorrect. The earth is actually an oblate spheroid, that is, a globe which is slightly flattened at the poles.  But the statement "the earth is round" is much closer to the truth than the claim that "the earth is flat."  

 

 

 

2. All matter consists of just four elements vs  All matter is made up of just electrons and protons.

Again, both are false, but the second statement is a lot less false than the first. Matter is certainly not just made up of  the four elements of earth, air, fire and water. But it's also not just made up of electrons and protons; matter is now known to be made up of neutrinos and muons, and up quarks and down quarks and charm quarks and who what knows other kinds of elementary particles still waiting to be discovered. The second statement is truer that the first, but physicists would not claim that it's the last word on the subject.  

3. Vitamins prevent cancer vs vitamins don't prevent cancer

Here is starts to get complicated. While some studies are pretty conclusive (no-one really suggests that smoking doesn't cause lung cancer) other scientific claims seem to change over time. For example, the relationship between vitamins (especially vitamin D) and cancer is one that we have had different scientific answers to at different times. In 1999 the N-HANES study of over 5,000 women followed for twenty years reported that vitamin D was associated with a reduction in breast cancer. Then in 2007 the Journal of the National Cancer Institute looked at a group of 36,000 women in the Women's Health Initiative.  It reported that there was no effect of vitamin D on the risk of breast cancer. Today, the official position of our National Cancer Institute is this: it still isn't sure if there is any association.

And now a forth scientific claim, this time from the field of mathematics

4. In a right angleD triangle, the square of the hypotenuse is equal to the sum of the squares of the other two sides.

This theorem (like all mathematical theorems) is true in a special way. So long as we're talking about two dimensional geometry, then this theorem will be true in all possible places in the universe; it was always true in the past, and it will always be true in the future.  That's what makes a mathematical theorem true in a different way from a medical truth, or a truth about the physical universe.  The latter two may be partially true, or true of the basis of the best equipment we have available, but these are not true in the way that the Pythagorean theorem is true.  

KINDS OF SCIENCE

So there are different kinds of scientific claims, some of which are more true than others. And scientific progress advances in different ways depending on which area of knowledge we are addressing.  These differences were not noted by any of the rabbinic critics we've cited above, but once understood, they allow us to appreciate that science can make different claims over time and that some of these can change without the entire scientific enterprise being called into question.

One last thing- be careful of any appeal to relativism. It could be argued that each of the rabbis we cited (well, other than Rabbi Meisleman) lived at a time when these subtleties were not appreciated. As a result we should not be a harsh judge of their philosophies of science, which just reflect the way people thought at that time.  I am sympathetic to this claim, and I think it is a perfectly reasonable explanation of how they may have arrived at their opinions. But if these rabbis were just reflecting the way everyone thought when they lived, we are most certainly not bound to consider these opinions as anything other than of  historical  interest.  And since we now know differently, we can ignore these rabbinic opinions as we forge our own Jewish philosophies towards science.  If, on the other hand, the claim is made that these rabbis were reflecting a profound Jewish Truth that will remain so for ever, well, then we have a problem. Because you are then forced to reject the science, and end up arguing for all kinds of things we know are simply not true.

One other last thing. This is not a claim that science is the only path to knowledge, happiness and enlightenment.  I am not suggesting anything like that.  Steven Pinker argued for something  along these lines in the pages of The New Republic (ז'לֹ), and Leon Wieseltier wrote a persuasive  response, both of which are well worth reading.  (I find myself more sympathetic to the latter than the former.) But when it comes to scientific questions, well, that is where science does, perhaps know best.

“Science confers no special authority, it confers no authority at all, for the attempt to answer a nonscientific question.”

— Leon Wieseltier

where we've been

We noted that 130 years ago the laws of Yibbum were explained with a scientific fact that today we know is incorrect. This example shows that the scientific enterprise is only ever tentative and should be best ignored when it seems to raise questions about Jewish teachings. We examined six rabbinic understandings of the philosophy of science, but noted that they do not capture the different meanings we have when we way that something is a fact of science. 

We need some new Jewish philosophies of science. There have been some really good efforts to address this area (like here and here and here), but more work needs to be done. 

next time on Talmudology

Had enough about rabbinic attitudes to the philosophy of science? OK, next time we'll talk about snakes.

Ta’amei Hamitzvot in the British Medical Journal: The Deceased Wife’s Sister Controversy: Part II

Last time on Talmudology

In Jewish law, a man may marry his dead wife’s sister, but in Victorian Britain it remained against the law (unless you were a Duke). But many ignored the law, and there was a strong movement to change it. Here’s what happened next, but first a personal revelation...

My own great grandfather married his dead wife's sister!

It's true.  I have skin in this game.  I am the direct descendent of a man who married his dead wife's sister. My great-grandfather, Solomon Bograchov married, moved to London (from Odessa?) and had two children. But his wife died, and, so the story goes, he called for his wife's younger sister to come to London and marry him.  Which she did. They had three children, one of whom was Johnny, born in London in 1913. And Johnny was my zaide.

For clarity, not all family members are shown.  

Now back to our regularly scheduled programming

Hook's Church Dictionary vs the British Medical Journal on Ta'amei Hamitzvot

Hook’s Church Dictionary, first published in 1842, was a wildly successful reference manual for the clergy of the Church of England. But its 1887 fourteenth edition contained a controversial new entry. 

The new edition tackled the key social issue that we have already discussed: should the law be changed to allow a man to marry his deceased wife’s sister? Absolutely not, said Hook’s Church Dictionary. And it supported this opinion by comparing it with what we call Yibbum, that is, the act of levirate marriage, which "was not, properly speaking, permitted by the Jewish law at all." (This is partially true, since marrying a husband's brother was forbidden in Leviticus 18:16.) This prohibition "was a general moral law" and so applied to all mankind, and was only to be overridden in the special case of a married man who died without children. In this instance, The Bible (Deut. 25:5-10) requires levirate marriage so as to "protect those agrarian rights which were at the basis of the Hebrew system.” But at its core, the Bible’s prohibition against marrying a brother’s wife was precisely the same as the Church’s prohibition against a man marrying his deceased wife’s sister.  Precisely the same.  And what would happen if that Church prohibition would be changed? It would lead to the end of society as we know it. Really, I’m not making this up; that’s what it said:

“To legalize marriage with a deceased wife’s sister cannot possibly remain a solitary innovation. We shall have …taken the first step in a revolution of the whole of our domestic and much of our social life.”

Which brings us, at long last, to The British Medical Journal.

Writing in The Journal, an anonymous doctor -“a surgeon of twenty-five years standing” -challenged this entry in Hook's Church Dictionary, and he used the best science of his day to do so.  The reasons for God’s laws, wrote the surgeon,  “will be found closely connected with some physiological law…and …what profound knowledge was possessed by the framer of Mosaic law, because the facts upon which the opinion is based have only recently appeared in the annals of science. “

He stated that the science at the basis of the laws of Yibbum was the laws of heredity.  Since children inherit the “proclivities of their parents,” a marriage of close blood relatives (consanguine marriage) would concentrate any undesirable traits, and “cause the race to deteriorate.” But when a man marries his dead wife’s sister, he is not marrying a close relative. In fact, he not marrying a blood relative at all, and any offspring would not carry the concentrated negative traits of their parents.  As a consequence, these marriages should be permitted. (Remember that the author was writing some six decades before the discovery of DNA, and only a few years after Mendel’s (largely ignored) suggestion that there were recessive and dominant “factors” that carry hereditary characteristics.)

But when a man marries a woman who has fathered children with another husband, something else is at work, scientifically speaking. “The fact may be regarded as well established that…traces of the first child’s father are discoverable in all succeeding children of the same mother, whatever the direct paternity of these may be.”

Got that? When a man impregnates a women, some of his traits are carried to all the future children of that woman, regardless of who the next father may be.  It is for this reason that the Bible prohibited a man from marrying his dead bother’s wife - unless that brother had fathered no children. For if the deceased brother had fathered a child, his traits would be carried by his wife in all her future pregnancies.  If a man would then marry his widowed brother’s wife, she would pass on both his traits and those of her former husband in a concentrated form. The effect on heredity would be exactly the same as marrying a close blood relative, since the undesirable traits (this time from two brothers) would be mixed together and passed on.  

By the powers of this science, the surgeon then addressed the issue of the day. He argued that no such effect would occur if a man were allowed to marry his dead wife’s sister. “The father has no similar power of transmitting traces of his former wife to the children of her successor, for the diseases which are occasionally contracted by contagion are quite distinct from the collaterally inherited traits referred to.”

Ta’amei Hamitzvot in the BMJ

It’s all very neat and scientific. Levirate marriage was a special dispensation and when understood through the science of heredity, it made biological sense. Since the dead brother had fathered no children, his traits were not carried by his wife, and she could marry her brother-in-law without being worried that there would be a concentration of bad blood. This same cutting edge science also supported a change in the law that would allow a man to marry his dead wife’s sister.

“The effect produced upon the ovaries by impregnation is not only special upon the particular ovum which becomes developed into the particular child begotten, but general upon the entire mass of at least one, if not both…But where impregnation has failed to take place no such effects can follow....”

But we know that no such effect exists. Not remotely.  (And don’t write to me about infectious conditions; we’re not talking about those.)  Today, we know that the science in The BMJ was wrong. Which makes us question the nature of scientific knowledge itself.  It is, as this example shows,  unreliable.  What is true for science today turns out to be wrong tomorrow. And so, when the Torah and Jewish tradition faces a challenge from the scientific community, the correct response is to ignore the science, because hey, in a few years, there will be another scientific theory that comes along and replaces the one that is troubling to us. Right?

Find out in the next installment, on Talmudology. 

Science, Torah, and The Deceased Wife’s Sister Controversy: Part I

For the last seven pages, the talmud has been analyzing one phrase in the Torah (Lev. 18:18):

וְאִשָּׁ֥ה אֶל־אֲחֹתָ֖הּ לֹ֣א תִקָּ֑ח לִצְרֹ֗ר לְגַלּ֧וֹת עֶרְוָתָ֛הּ עָלֶ֖יהָ בְּחַיֶּֽיהָ׃

Do not take [into your household as a wife] a woman as a rival to her sister and uncover her nakedness in the other’s lifetime.

The Plan

We are going to discuss what we mean when we say that science changes. We are also going to look at some Jewish skeptics of science, and their understandings and misunderstandings of the concept of a science that changes.  We’re going to do this through the lens of Yevamot, and examine in some depth The British Medical Journal’s understanding of Ta’amei Hamitzvot, the reasons for the commandments in the Torah. But to do so will require a detour into a fascinating social debate that took place in Victorian England. We are going to dive deeply. So strap in. (Yes I know. Too many metaphors. Sorry.)

Background – Yevamot 8a.

In Leviticus (18:18) the Torah states

"ואשה אל אחתה לא תקח לצרר לגלות ערותה עליה בחייה".

You shall not take a women with her sister to become rivals, to lay bare her nakedness, while her sister is still alive. 

Based on the word בחייה – is still alive, the Talmud in Yevamot (8b) established that a man may marry his wife’s sister if, and only if, his wife had died.  

This is reflected in the Code of Jewish Law, the Shulchan Aruch, which ruled (as did Maimonides) that the prohibition against a man marrying his wife’s sister exists only while his wife is alive. On her death, a man may marry his deceased wife’s sister. 

 אחות אשתו אסורה לו מן התורה, כל זמן שאשתו קיימת, לא שנא אם היא אחותה מן האב או     מן האם,  ואפילו גירש את אשתו. אבל לאחר מיתתה, מותר באחות

(שולחן ערוך אבן העזר הלכות אישות סימן טו סעיף כו) 

Just to be clear – this is not the central focus of Yevamot, which is concerned with levirate marriage; that’s when a man marries his dead brother’s widow; but it is very important since it will touch on issues central to science and Yevamot.  Let’s see how.  

Was Henry illegitimate?

The Jewish law allowing a man to marry his dead wife's sister was not followed in Victorian England. Quite the opposite - a marriage like this was forbidden. But a debate about this law began with a question about the the legitimacy the Duke of Beaufort. Henry Somerset (d. 1853) the seventh Duke of Beaufort, had married Georgina Fitzroy and had fathered two girls with her. But Georgina died in 1821, and the sad Duke then married her younger half-sister Emily, with whom he had a further six daughters, and a son. (I know this is beginning to sound like a complicated episode of Downton Abbey, but bear with me. It’s worth it.)  That son was Henry Charles FitzRoy Somerset (1824-1899), who later became the 8th Duke of Beaufort. But there was a problem. Perhaps Henry was not a legitimate heir to the House of Somerset, since he was the child of a union of a man and his wife’s sister (or in this case, half-sister.) If the old Duke’s marriage to his dead wife’s (half-) sister was prohibited, then Duke Henry was a bastard child and his inheritance would have to be passed on to other males in the family line. There was a lot at stake.

The solution came with the 1835 Act to render certain marriages valid and to alter the law with respect to certain voidable marriages, introduced by Lord Lyndhurst. This Act retrospectively made any marriage like the old Duke’s valid, but prohibited any such marriages from taking place in the future.  In this way, the present Henry, Duke of Beaufort, was not a bastard child after all; he could inherit the estate, and all was made good.

Except that it wasn’t. The Act did not settle matters at all, and ignited a debate in England that lasted seven decades. 

“In addition to regular parliamentary bills and debates, pamphlets, letters, treatises and statements from all sides were published steadily through this period; major journals carried articles from leading figures in the controversy…and at least five novels took marriage with a deceased wife’s sister as their explicit subject ”

— Wallace, Anne D. “On the Deceased Wife’s Sister Controversy, 1835-1907."

The Chief Rabbi and the Royal Commission

In 1842, and almost every year after that, the British Parliament debated whether to legalize the marriage between a man and his dead wife’s sister. Queen Victoria appointed a Commission to look into the whole thing, and look it did, producing a report of over 150 pages in 1848.  Buried in that report is a letter from the Chief Rabbi Nathan Adler, who made the Jewish position very clear.

“...the marriage of a widower with the sister of his deceased wife… is not only not considered as prohibited, but it is distinctly understood to be permitted, and on this point neither the Divine Law, nor the Rabbis, nor historical Judaism leave room for the least doubt.”

— Chief Rabbi Nathan Adler, Appendix to the Report of the Commissioners appointed to inquire into the state and operation of the Law of Marriage

It didn’t much matter. The law remained the law, though it seemed that the British public ignored their learned lawmakers.  In one 1849 parliamentary debate, it was estimated that there were some 13,000 such marriages. These marriages in turn produced about 40,000 children, all of whom were, by Victorian standards, bastards.

Things became especially heated in the late 1870s when some 3,000 farmers (all, apparently from Norfolk – what was happening in Norfolk?) signed a petition “praying for the legislation of marriage with a deceased wife’s sister.” And so, in May 1879, the Prince of Wales himself introduced a bill to legalize this marriage in Britain’s Parliamentary upper chamber, the House of Lords. Their lordships droned on, and on, and on (the transcript takes up some eight pages of single space font) until the measure was struck down in a vote: “Contents 81: Not-Contents 101”.

But even in England, things do change, and by the beginning of the twentieth century, Parliament was ready to legalize what many women were already doing with their dead sister’s husband. The Deceased Wife’s Sister’s Marriage Act of 1907 was passed, and British law finally caught up with that of the Talmud.

---

Next time:

The scientists weigh in on the Marriage Act as we look at The British Medical Journal and its understanding of Ta’amei Hamitzvot and Yibbum.

Yevamot 97a ~ Rava on Delayed Puberty in Boys

Several days ago (in Daf Yomi time) we read of Rava's observation that delayed puberty may be related to body mass:

כי אתו לקמיה דרבא אי כחוש אמר להו זילו אבריוהו ואי בריא אמר להו זילו אכחשוהו דהני סימנין זמנין דנתרי מחמת כחישותא וזמנין דנתרי מחמת בריותא

Whenever people came to Rava [with a case of a man who had not developed pubic hair]  he would tell them, if [the man was] thin, ‘Let him gain weight’; and if they were overweight he would say ‘Go lose weight’; for these signs [of sexual maturity] are sometimes delayed as a result of emaciation and sometimes  as a result of obesity.   (Yevamot 97a)

There has been some discussion of what appears to be the increasingly earlier onset of puberty in girls. In fact, menarche, (the age of a girl's first menstrual period) has been steadily decreasing by a consistent three years per century of record keeping. However, Rava was addressing not the early onset of puberty in girls, but its delayed appearance in boys.  He noted that this delay was sometimes related to extremes of nutritional status, and so in these cases, was amenable to intervention.

“Rava may have been the first first to report an association of obesity and delayed puberty in boys.”

Rava was on to something. He may in fact have been the first to report an association between obesity and delayed puberty in boys.  This association has been confirmed by several studies which found that obesity has different effects on puberty in boys and girls. In girls, obesity is associated with earlier puberty, while in boys it has the opposite effect, and delays sexual maturation. But it was not until 2010 this association was confirmed by a longitudinal population-based study. This reported that a "higher BMI z score trajectory" (i.e. obesity)  during early to middle childhood may be associated with later onset of puberty among boys. 

Rava also claimed that puberty may be delayed in boys who are underweight, and this has also been confirmed. As far as I can tell, none of the researchers has credited Rava (who died around 350 CE.) for being the first to notice these associations. But Rava was first, and firsts count for something in science.

POSTSCRIPT

The same passage is repeated in Bava Basra (155b) but in the name of Rabbi Hiyya.  Hiyya probably lived in the second half of the second century, and so predated Rava by a few decades.  The claim of primacy regarding the association with nutritional status and delayed puberty may therefore have to be extended back to R. Hiyya.  But so far I have found nothing in the works of Hippocrates, Aristotle and Galen that address this issue, so this association does not appear to have been a widely held belief in antiquity that was simply being echoed in the Talmud. As all good scientific papers end, further research is needed...