Had you asked [Jesus] if there was a literal Adam or Eve and serpent, I think he would have been puzzled by the 'literal' tag, but I suspect that if you had pressed him he would have said that he believes in a literal Adam and Eve (though I cannot prove these statements. I am making historical judgments, and I see no reason why he would not have believe these things – modern science did not develop for centuries. Though as noted, the whole metaphorical / scientific categorisation would have probably puzzled him).This is not an issue of scientific knowledge, it is one of literal versus allegorical.
Jesus was familiar with the Old Testament besides Genesis. He frequently quoted Deuteronomy and mentions the prophets. The Old Testament had plenty of material that was understood to be figurative. In the book of Judges we read of Gideon's son Jotham telling his half brother Abimelech a story of the trees having a council:
The trees once went out to anoint a king over them, and they said to the olive tree, 'Reign over us.' But the olive tree said to them, 'Shall I leave my abundance, by which gods and men are honored, and go hold sway over the trees?' And the trees said to the fig tree, 'You come and reign over us.' But the fig tree said to them, 'Shall I leave my sweetness and my good fruit and go hold sway over the trees?' And the trees said to the vine, 'You come and reign over us.' But the vine said to them, 'Shall I leave my wine that cheers God and men and go hold sway over the trees?' Then all the trees said to the bramble, 'You come and reign over us.' And the bramble said to the trees, 'If in good faith you are anointing me king over you, then come and take refuge in my shade, but if not, let fire come out of the bramble and devour the cedars of Lebanon.' (Judges 9)This is more than a thousand years before Jesus yet these people understood fable. In fact trees seem to be a recurrent theme in the Old Testament with Joash sending a message to Amaziah concerning a cedar and a thistle (2 Kings 14, 2 Chronicles 25), and God informing Ezekiel about an eagle removing the upper twigs of a cedar to a different land (Ezekiel 17). Jesus certainly would have been familiar with these passages.
Moreover, Jesus frequently spoke in parables himself. He didn't just inform people of theological truths but made use of stories to illustrate these truths. Matthew adds,
All these things Jesus said to the crowds in parables; indeed, he said nothing to them without a parable. (Matthew 13)The parable of the sower is a good example. This parable uses symbols thru-out: sower, soil, birds, rocks, thorns, birds—all symbols of some other thing.
The clincher that Jesus both understood and affirmed the literalness of Adam and Eve is seen in his description of John the Baptist. The Old Testament closes with a prediction of God's visitation and his forerunner Elijah:
"Behold, I send my messenger, and he will prepare the way before me." (Malachi 3)
"Behold, I will send you Elijah the prophet before the great and awesome day of the LORD comes." (Malachi 4)Now this could be interpreted as either Elijah returning (as he ascended to heaven in a whirlwind) or as a person coming in the ministry of Elijah. We are told it is the latter in the gospel of Luke; the fulfilment in the person of John the Baptist:
And [John] will turn many of the children of Israel to the Lord their God, and he will go before him in the spirit and power of Elijah, (Luke 1)Jesus affirms this,
As they went away, Jesus began to speak to the crowds concerning John: "What did you go out into the wilderness to see? A reed shaken by the wind? What then did you go out to see? A man dressed in soft clothing? Behold, those who wear soft clothing are in kings’ houses. What then did you go out to see? A prophet? Yes, I tell you, and more than a prophet. This is he of whom it is written,Jesus applies Malachi 3 to John and Jesus specifies that John is Elijah. From this we can note that Jesus is perfectly able to understand that a passage can have figurative aspects to it. Jesus does not think that John is literally Elijah or that Malachi meant that Elijah would literally return. And Jesus thought this is even though several of his contemporaries thought that Elijah would literally return." 'Behold, I send my messenger before your face,/Truly, I say to you, among those born of women there has arisen no one greater than John the Baptist. Yet the one who is least in the kingdom of heaven is greater than he. From the days of John the Baptist until now the kingdom of heaven has suffered violence, and the violent take it by force. For all the Prophets and the Law prophesied until John, and if you are willing to accept it, he is Elijah who is to come. He who has ears to hear, let him hear. (Matthew 11)
who will prepare your way before you.'
So when Jesus claims that Adam was a real person he is fully able to comprehend the difference between this and the concept that Adam fictitious person representative of humankind. He is able to understand whether the creation story is historical or mythological. This is not surprising as Genesis clearly historical narrative and Joash's story is clearly allegorical. Malachi may be more subtle but that is often the case with prophecy; that Jesus is aware of this subtlety demonstrates our thesis more strongly.