Identical Twins: Yaacov and Esav

The tale of the quarreling brothers Yaacov and Esav is one of extreme differences. Esav is wild and hairy, Yaacov is simple and fair. Obviously the text implies that these twin brothers were not identical however careful reading coupled with an understanding of modern medicine paints a very different and consequential picture of these identical twins. 

There are two types of twins, dizygotic and monozygotic. Dizygotic twins occur when the mother has two separate eggs fertilized. These fetuses will have two unique sets of genes and therefore not be identical and in fact can be opposite genders. Monozygotic twins derive from one maternal egg that divided into two fetuses. This results in the two fetuses having identical genes and are therefore colloquially ‘identical’ twins. 

Monozygotic (identical) twins have additional subtypes. If the egg splits before it implants into the endometrium then the twins will be dichorionic and diamniotic (DiDi), meaning they have separate placentas and amniotic sacs. Each child develops independently with less risk to the fetuses. If the egg splits soon after implanting into the endometrium then the twins will share a placenta but have two separate amnion, called monochorionic diamniotic (MoDi) twins. These twins might partly share a blood supply. If the egg splits a little later after implantation the twins will share a placenta and amniotic sac, termed monochorionic monoamniotic (MoMo) twins. These twins have a very high chance of sharing a blood supply and also suffer increased fetal risks due to the fact that they share an amniotic sac allowing them to physically interact with each other. If the egg splits any later after implantation this will result in monochorionic monoamniotic twins that may also share physical parts of their bodies, known as conjoined twins. The more delayed this split occurs results in a greater degree of conjoining.

The text describes Yaacov and Esav as physically distinct, seemingly implying dizygotic, non-identical, twins. Esav was born red and hairy (25:25) and later we learn that Esav remains quite hairy while Yaacov is smooth (27:11). Esav’s redness is never mentioned again after his birth so appears to have been temporary. These are very intriguing details as a very common complication of MoDi and MoMo pregnancies is Twin-to-Twin Transfusion Syndrome (TTTS). Due to the shared placenta the blood supply is often asymmetric resulting in dangerous differences of blood volume for each twin. Often one twin will be a donor to the other. This results in the donor being anemic, lacking blood, and often developing more slowly and growing smaller than their twin. The twin that receives the extra blood is polycythemic, red due to the extra blood and more developed than their twin.

The symptoms of TTTS perfectly match the birth description in the text as not only was Esav more developed (hairy) and red but we also learn that Yaacov was grasping the ankle of Esav as he was delivered first (25:26). This can only occur if there is no physical separation within the womb between the twins, which can only occur in MoMo twins. This type of twinning also greatly increases the chances of TTTS. A further hint of TTTS derives from the abnormal amount of fetal activity during Rivka’s pregnancy (25:22). She suffered so much from the fetal activity that she regretted wanting to become pregnant. This abnormally increased fetal activity may be related to the fact that the fetuses were physically touching each other as in a MoMo twinning. 

It is quite evident that the brothers were identical twins, yet they were remarkably physically different in their later years. Specifically, Esav was still significantly hairier than his smooth twin (27:11). This can possibly be explained by another interesting textual detail. Esav grew to be an outdoorsman and avid hunter while Yaacov led a simple indoor life (25:27). One’s lifestyle choices have tangible effects on the body, whether due to muscle building from physical labor or defensive compensations for environmental irritants, such as callous formation and hair growth. The opposite is true as well with a sedentary indoor lifestyle leading to fairer and lighter skin as was seen with the ‘blue bloods’ of medieval European aristocracy. While likely exaggerated by the text (27:16,22-23), nonetheless, there was likely a tangible difference to the material texture of Esav’s arms relative to Yaacov. 

The fact that Yaacov and Esav were identical twins serves to highlight even more the dangerous family dynamics that derive from quarreling over power, inheritance and succession. One would think that twins, more than regular siblings, would be most likely to get along. All the more so that identical twins would be the most likely to be equally adored and equitably treated by their parents. Yet, the text emphasizes the exact opposite due to the fixation of everyone in the family of the ultimate necessity to pass the estate of Abraham onto only a single descendent. Yaacov would later come to recognize the errors of this mindset when he literally fights himself and ultimately realizes the futility and self destruction that is familial discord (see “Who did Jacob Truly Wrestle and Why was his Reward a Name?”). Ultimately making peace with Esav and passing his estate equitably amongst all of his children.