Capsaicin Defense

Chili peppers produce capsaicin to deter mammals, whose teeth crush seeds before they can sprout. Birds do not feel the burn and swallow the seeds whole, dropping them intact far from the parent plant. The plant evolved one chemical that turns away the wrong carrier and welcomes the right seed-dispersal partner.

An Evolutionary Orphan

Avocados are a puzzle. Their huge seeds are too large for any living animal to swallow whole. The leading explanation is that avocados once relied on giant ground sloths and gomphotheres, megafauna that died out around 13,000 years ago. With its partners gone, the avocado was left an evolutionary orphan, kept alive only by human cultivation.