I can't prove it, but I believe the first man was a woman.
Modern science has used mitochondrial DNA to track human origins back to a single female. This is the so-called Eve hypothesis.
I believe that this was the first fully human Homo Sapiens. A girl was born with a genetic "defect" in her mitochondria. The mitochondria control the enzyme activity in the cell. This change affected her metabolism at a deep cellular level.
The first human had an altered metabolism that manifested itself in a suite of gross differences:
She lacked vibrissae, the sensory whiskers common to all other mammals.
She had full lips, not the thin line at the rim of the mouth typical of other species.
She was weak, compared to others of her kind.
Her features retained a more child-like appearance as she grew up.
But, the two most critical differences were a lack of body hair, and a monthly estrus cycle.
Why are the last two most critical?
The lack of body hair provided an interesting advantage. To understand this, let's look at cats. There is a breed of hairless cat. Instead of fur, they have a velvety skin. Their owners often comment on how affectionate their cats are. Affectionate? Not really, these cats are just COLD, they snuggle to keep warm!
Back to our first human, she sure is cuddly. She is much more desirable than her standoffish hairy sisters.
Rather than the annual fertility cycle, she is 'in heat' all of the time. Cuddly and friendly too!
Lacking muscle strength, she needed to be protected. The beginnings of love as we now understand it.
That she needed protection is deeply ingrained it the human psyche. In propaganda there are surprisingly few common themes. The enemy is depicted as snakes, spiders, octopus, and, ... and ... hairy ape-men seizing the furless women. The massive muscular King Kong is interested in the petite Fay Rae. Did you ever wonder why this resonated with the audience?
Simple. The first man was a woman...
I noticed that you put 'in heat' into quotes, suggesting that you didn't mean that literally. However, we get some folks making the oddest statements around here so I would like you to clarify the point.
Human females do not experience anything similar to going into heat as do other mammals. They can, of course, become aroused at any time. I believe this is what you meant. Correct?