It seems Rebekah's twin pregnancy was not easy. The phrase 'the babies jostled each other within her' (Gn 25:22), is hard to put into medical terminology but suggests unusually violent foetal movements. This foresaw the momentous future conflict between Esau and Jacob- and their descendants (Gn 25:23). In the Bible narrative, God's involvement with his people starts, not at birth, but before. Interestingly, this perspective is supported by advances in fetal physiology, emphasising the importance of intrauterine events in development.

At birth the babies' appearances were very different. Esau was described as both 'red' and 'hairy', hence to his biblical names of 'Esau' (hairy) and 'Edom' (red). A marked rubor of the skin at birth usually indicates polycythaemia and may be a useful clinical sign. Twin-to-twin transfusion occurs due to an abnormal placental vascular connection, resulting in one twin losing blood cells into the other's circulation. This can produce anaemia in the donor and polycythaemia in the recipient. However, this phenomenon only occurs in identical twins. From the biblical evidence it seems unlikely that Jacob and Esau were monozygotic; not only were their appearances (both at birth and in adult life) but their personalities were constantly at odds (Gn 25:27-28).

The other common cause of polycythaemia at birth is placental failure leading to chronic mild foetal hypoxia. This causes excess erythropoeitin release and increased red cell production in the bone marrow. A degree of placental failure is a common in twin pregnancy.

Finally, Esau's name may instead have described his hair colour. Perhaps, then as now, a fiery temperament and ginger appearance were seen as related. Whatever the explanation, in God's providence the differences between Esau and Jacob symbolised an ultimate and mysterious divide in God's covenant love. As both the prophet Malachi and the apostle Paul spelt out, 'Jacob I loved, but Esau I hated.' (Mal 1:2,3; Rom 9:10-16)