Evolutionary Anachronism

The avocado may be an example of an 'evolutionary anachronism', a fruit adapted for ecological relationship with now-extinct large mammals (such as giant ground sloths or gomphotheres). Most large fleshy fruits serve the function of seed dispersal, accomplished by their consumption by large animals. There are some reasons to think that the fruit, with its mildly toxic pit, may have co-evolved with Pleistocene megafauna to be swallowed whole and excreted in their dung, ready to sprout. No existant native animal is large enough to effectively disperse avocado seeds in this fashion. If so, the avocado occupies an ecological niche similar to that of the mango of Asia.

Basically, this tree evolved because there was an animal large enough to poop out the seeds in dung from which it could sprout? Something to think about when you're cutting them open and trying to grow them.

It's also interesting that they're not toxic to us.

The form of the avocado fruit today may be more of a result of a past ecological relationship with magafauna than the current relationship with humans, monkeys, and other extant animals. Barlow (2002) posits that the avocado is "haunted" by the "ghosts" of the glyptodonts, toxodons, gompotheres, and groundslots. The Persea species that live along the Gulf Coast have fruit that are about the size of blueberries, small in comparison to the avocado. Avocado pits are soft and unprotected, unlike other fruit tree seeds such as canistel (Pouteria campechiara), which has a mild-flavored seed with a tough coating. Instead, the avocado relies on bitter toxins to deter damaging the seed through digestion. The avocado pulp also contains laxaitives, which quicken the seed's trip through the animal's digestive system, reducing the chances of damage by the digestive juices. Only megafauna would have been large enough to swallow the fruit and the pit whole, which would have helped the avocado disperse its seeds. The seeds pass through in a "fertilizer" of feces. Today, elephants in Africa disperse fruit tree seeds through their feces, including the non-native avocado and American papaya (Carica papaya) (Barlow 2002).
http://blm.academia.edu/AmandaJLandon/Papers/406186/Domestication_and_Significance_of_Persea_americana_the_Avocado_in_Mesoamerica

So the biggest reason seems to be that the skin has laxatives which implies the whole fruit was eaten, skin and all. There is no existing native animal large enough to do this.

Ground sloths are a diverse group of extinct sloths, in the mammalian superorder Xenarthra. Their most recent survivors lived in the Antilles, where it has been proposed they may have survived until 1550 CE; however, the youngest AMS radiocarbon date reported is 4190 BP, calibrated to c. 4700 BP for Megalocnus of Cuba. They had been extinct on the mainland of North and South America for 10,000 years or more.

They think they evolved while South America was isolated. It was thought to be uninhabited by humans when people were crossing the Bering Land Bridge 15,000 years ago and they migrated south through the Isthmus of Panama.

So maybe in that 5,000 years or so, they were hunted to extinction and those hunters had the ability to eat the avocados? They probably also tracked these animals through their poop, etc.

So, the avocado represents how much of a threat we are.

http://upload.wikimedia.org/wikipedia/en/7/73/Giantslothtex1.JPG

This has also apparently affected the Devil's Claw which is another evolutionary anachronism related to extinct mammalian mega-fauna seed dispersal.
http://en.wikipedia.org/wiki/Acacia_greggii
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