In Guns, Germs, and Steel, what are the commonly espoused answers to Yali's question (other than the answer that Diamond suggests)?

Yalis question,
which is essentially, Why did some areas of the world develop wealth and
technology in greater quantities than others? has been answered several times
throughout history. Diamond himself asks on page 18, Does Yalis question really need another
book to answer it?" Obviously he believes so, and he proves his case by rejecting three
previous proposals before presenting the final potential answer that he believes is much more
likely.

1. Per Darwinian evolutionary theory, some sections of
humanity evolved to be physically or intellectually superior to others. The
Europeans are more highly evolved than other populations of the world. This is rejected, as
there is no evidence to support this claim, and it boils down to modern-day racism. It is
difficult to assess the average IQ of an entire population, and intelligence can be measured
differently between populations.

2. Cold climates require more
innovation than warm climates. While this would support a Northern European
answer to Yalis question as to why Europe was more technologically advanced that other areas,
this is also rejected. Warmer climates had their share of innovation, as Diamond cites the
development of writing, pottery, and agriculture in areas not previously considered cool enough
to require stricter innovation.

3. As evidenced by the Fertile
Crescent, the Nile, the Indus, and the Yellow and Yangtze Valleys, agriculturally productive
environments created more complex and centralized forms of government. In fact,
Diamond argues that this chicken and egg question goes the other way and that agricultural
abundance (in the form of complex irrigation systems) comes after centralized government,
according to modern archaeology.

4. The fact that Europeans had
guns, infectious diseases, steel tools, and manufactured products appears to be
the correct answer, according to Diamond. This is why Europe developed more wealth and
technology than other areas of the world, and this can be proven through multiple methods. That
being said, Diamond acknowledges that this is not a sufficient answer to Yalis question, and he
will spend the rest of the text exploring this particular answer.