The most common and most likely answer to this crossword clue is the 4 letter word PRAM
I've seen this crossword clue in The Daily Telegraph
P
R
A
M
More clues leading to the result PRAM
- Carriage for very young artist received by Prime Minister
- Drive after parking vehicle used by mum
- Heartless Trojan means to transport infants
- Jack’s about heading for Russia in Baltic vessel
- Vehicle used by mum takes dad to Paris – not the centre
- Buggy — no round in middle of golf tournament?
- Agatha Christie detectiveturned over carriage
- Earliest form of human transport?
- Vehicle traverses ramp
- One gets pushed by positive force
Buddy explains!

The straight part
We know that "Earliest form of human transport?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case earliest form of human transport? = pram.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does PRAM mean?
PRAM noun- A small vehicle, usually covered, in which a newborn baby is pushed around in a lying position; a perambulator.
- A flat-bottomed barge used on shallow shores to convey cargo to and from ships that cannot enter the harbour.
- A similar barge used as platform for cannons in shallow waters which seagoing warships cannot enter.
- A type of dinghy with a flat bow.