The text below was a response by Marko Marina in a BSA conversation here.
Like most critical scholars today (Catholic and non-Catholic alike), I’m [Dr. Marina] convinced the figures called “brothers” of Jesus in the New Testament were in fact his biological siblings, children of Mary and Joseph born after Jesus’ birth. Below, I’ll respond point-by-point to the reasons you find the older “cousin theory” persuasive and show why it no longer convinces professional historians or philologists.
1. The language problem:
a) In Koine Greek, ἀδελφός almost always means a blood brother. For a different reading, you’d need clear contextual clues, which are lacking in the case of Jesus’ brothers. Moreover, there is a different word in Greek for “cousin”. It’s ἀνεψιός. Interestingly enough, Paul (or whoever wrote Colossians) used this term, mentioning Mark, the cousin of Barnabas (Col 4:10)
b) No NT author ever used ἀδελφός for a “cousin”. That includes Mk 6:3 and John 7:5. As a great Catholic scholar, John P. Meier observed, reading, for instance, Mk 3:17, which mentions “καὶ Ἰάκωβον τὸν τοῦ Ζεβεδαίου καὶ Ἰωάννην τὸν ἀδελφὸν τοῦ Ἰακώβου” (James the son of Zebedee, and John, the brother of James), no one would ever argue that the author of Mark’s Gospel was actually claiming that John was James’ cousin, not a brother. However, people today would argue that in the case of Jesus’ brothers, it is not because there is evidence for that in our texts. Rather, it’s because of the later doctrinal developments (see below).
c) Jerome’s appeal to Hebrew/Aramaic imprecision fails! Aramaic may lack a distinct word for cousin, but the evangelists were writing in Greek, and there is no evidence that, for instance, Mk 6:3 bears clear Semitic traces. Moreover, where Hebrew syntax intrudes (e.g., LXX Genesis 13:8), the context always signals the broader sense or meaning of the word ἀδελφός. Mark 6:3 gives no such signal!
2. Why the “cross-references” don’t line up:
This is a bit trickier because Jerome’s complex theory needs to be unpacked. You cited 5 passages to argue that the brothers of Mk 6:3 are the “James and Joses” found at the cross and tomb. However, several things need to be exposed here:
a) “James the Younger” is never a title for James the Lord’s brother in any 1st or 2nd-century source. The Lord’s brother is instead called “James the Just” or simply τὸν ἀδελφὸν τοῦ κυρίου (Gal 1:19; Hegesippus, Hist. eccl. 2.23.4). James the Younger is called that way precisely so that he could be differentiated from other people bearing the same name, including (most famously), James the brother of Jesus.
b) The author of Mark distinguishes between two families. Jesus’ nuclear family in Nazareth (Mk 6:3) and another Mary with her own sons at the cross (Mk 15:40). Conflating them is the lynchpin of Jerome’s theory, and it does not survive careful source-critical reading.
3. The Clopas/Alphaeus hypothesis is, at best, speculative:
Jerome needs Clopas = Alphaeus to turn the second Mary’s sons into apostles and thus “explain” their fame. However, this equation rests solely on late patristic guesswork and a doubtful etymology. Even if Clopas were Joseph’s brother, being first cousins still would not explain why every gospel repeatedly calls the men adelphoi rather than “sons of Clopas.”
4. Other evidence cuts against the “cousin theory”:
Hegesippus (c. 170 C.E.) calls James and Jude “brothers of the Lord according to the flesh”. More importantly, elsewhere Hegesippus uses the word ἀνεψιός when he means “cousin”. The fact that he distinguishes these two terms shows how he understood kinship. Furthermore, Josephus (a “neutral” Jewish historian with no investment in any of the Christian doctrinal beliefs) refers to “James, the brother (ἀδελφός) of Jesus who was called the Christ.”
The Helvidian position (“literal/real brothers”) was popular and acceptable until later doctrinal developments and until Jerome’s counter-tract Against Helvidius, written at the end of the 4th century. But here is the crucial point (or two points)
1. Jerome’s motive was theological. He was defending the idea of Mary’s perpetual virginity from the perspective of a vigorous ascetic who believed that asceticism (which includes celibacy) was, by far, the superior way of life. Thus, it is absolutely clear that he projected his own ascetic “ideology” into the 1st-century context.
2. We have his work Against Helvidius, and it’s indicative that Jerome, in defending his position, made things up (to put it mildly). For instance, he claimed that Ignatius of Antioch, in one of his epistles, defended the “cousin theory”. That’s not the case at all. Ignatius never even addressed this issue!
5. Historical-social objections:
a) “Seven children in a poor Galilean village are medically improbable.” Actually, Jewish women bore 5 to 6 or even 7 children; high infant mortality meant having many births to secure lineage.
b) Regarding Luke’s story about only Jesus traveling is a theological device to showcase Jesus’ early wisdom (in the same case, other Greco-Roman authors would highlight early wisdom of various figures, such as Roman emperors). I’m not sure that this story goes back to the historical Jesus at all. But even if it does, the narrative silence is not evidence of non-existence, especially when Luke knows of the brothers (e.g., Acts 1:14).
6. Kinship terms in village life:
You suggest all children in an extended household were simply called “brothers” or “sisters.” Rural clans do blur kinship lines in practice. However:
a) Greek still retained ordinary precision. Even in tight-knit villages, papyrus evidence distinguishes ἀδελφός from ἀνεψιός when needed.
b) Paul had been in Jerusalem. He knew James personally, and he wrote to Greek-speaking congregations outside of Palestine. And still, he calls James “the Lord’s ἀδελφός”, not his ἀνεψιός (“cousin”) or even συγγενής (relative).
Conclusion:
Given these considerations, the overwhelming majority of critical scholars (including Catholics like John P. Meier, Joseph Fitzmyer, and Raymond E. Brown) hold that Jesus’ brothers were his actual brothers, not cousins. I remember lecturing on this a year ago. During the Q&A, a priest stood up and tried to defend Jerome’s theory. If you are really invested in this particular understanding of Mary’s perpetual virginity, no amount of evidence would persuade you. Our discussion lasted for about 20 minutes. In the end, he just couldn’t accept my arguments. But the reasons for his rejection had everything to do with doctrinal beliefs and theology, not history and philology.
Anyway, I hope I helped. If you want to know more about this issue, I’d suggest you take a look at works by Meier, Ben Witherington III, and John Painter. The latter wrote a scholarly biography on Jesus’ brother James.
