What's up with avocados?

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lightvector
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What's up with avocados?

Postby lightvector » Wed Jan 06, 2016 5:57 am UTC

Avocados seem pretty weird to me as fruits* go. In particular:

1. Why are they so fatty when so few other fruits that I've heard of have any significant fat content? (Maybe olives are one of the few others?)
2. Why are they not also very sweet?

Basically, what are the major underlying mechanisms behind why there are a huge number of sweet fruits and almost no fatty fruits, yet still a few notable fatty fruits rather than zero? Fat being a highly inferior strategy all-else-equal but in present in equilibrium at a tiny level due to more intense competition in sweetness? Avocados and olives actually being a lot sweeter originally except for human cultivation exaggerating the fattiness and reducing the sweetness? Some particular animal in the evolutionary environment that was ideal for seed dispersal that greatly preferred fats for some reason?

And I'm curious - do we know anything about the specifics for avocados in particular, beyond random happenstance? That is, what was the specific environmental pressure that caused avocados to go down the fat path, and furthermore kept it there by making it so that exchanging a little bit of fattiness for a little bit of sweetness was a net negative? What are the natural consumers of avocado fruits, or the fruits of their nearest wild ancestor? The best I could find was some speculative reference on wikipedia to giant extinct mammals - which doesn't make it obvious to how they survived long enough to be found and cultivated by humans.

*The definition of "fruit" that I think I mean here is something like "part of a plant containing or attached to the plant's seeds that is evolutionarily 'intended' to be consumed by animals as part of a reproductive strategy to disperse the seeds".

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Re: What's up with avocados?

Postby Angua » Wed Jan 06, 2016 7:56 am UTC

Meh, there are other not sweet fruit. Breadfruit just starch, for example. Christophene is just bland as hell. Ackee, I always thought tasted a bit like eggs. Clammycherry - makes a great glue but tastes like paint thinner (the one thing I've chosen here that is not routinely eaten in the Caribbean, however I have seen monkeys eating it).

You've got all the sour stuff as well.

You're probably right on the fat thing, but I think part of it is confirmation bias.
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Re: What's up with avocados?

Postby ijuin » Wed Jan 06, 2016 10:06 am UTC

Do any of the fruits in question use waterborne dispersal as a secondary method? If so, then the fat would allow them to float.

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Re: What's up with avocados?

Postby thoughtfully » Wed Jan 06, 2016 5:06 pm UTC

According to Wikipedia, there's a theory that the target dispersers were extinct megafauna.
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Re: What's up with avocados?

Postby Izawwlgood » Wed Jan 06, 2016 5:09 pm UTC

I still giggle whenever I remember they're berries.
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Re: What's up with avocados?

Postby poxic » Wed Jan 06, 2016 11:23 pm UTC

I thought I'd heard that avocados were technically nuts, but Google tells me that nuts are actually fruit. They're called nuts if they're dry and fruit if they aren't.

Also drupes, which are a type of berry with only one seed in them. So nuts are sort of drupes? This is why I didn't go into botany.
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Re: What's up with avocados?

Postby SAI Peregrinus » Thu Jan 07, 2016 3:27 am UTC

Avocados are toxic to birds, and therefore evil. It's also toxic to a lot of other animals, including cats & dogs. The pit & skin are more toxic than the flesh.

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Re: What's up with avocados?

Postby ahammel » Thu Jan 07, 2016 4:07 am UTC

poxic wrote:Also drupes, which are a type of berry with only one seed in them. So nuts are sort of drupes? This is why I didn't go into botany.

Drupes have a fleshy mesocarp (i.e., middle bit) whereas nuts are dry and do not. Just for more fun, there are all kinds of dry fruits which are not nuts because they shed their seeds spontaneously (capsules, legumes, etc.)
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Re: What's up with avocados?

Postby ijuin » Thu Jan 07, 2016 5:26 am UTC

SAI Peregrinus wrote:Avocados are toxic to birds, and therefore evil. It's also toxic to a lot of other animals, including cats & dogs. The pit & skin are more toxic than the flesh.


It's interesting how many toxic foods humans are able to tolerate. Indeed, we find many of them pleasant in small doses. You'd still get caffeine poisoning if you tried to eat half a kilogram of coffee beans in one meal though. But ten grams of them make for a nice broth.

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Re: What's up with avocados?

Postby tomandlu » Thu Jan 07, 2016 10:35 am UTC

ijuin wrote:
SAI Peregrinus wrote:Avocados are toxic to birds, and therefore evil. It's also toxic to a lot of other animals, including cats & dogs. The pit & skin are more toxic than the flesh.


It's interesting how many toxic foods humans are able to tolerate. Indeed, we find many of them pleasant in small doses. You'd still get caffeine poisoning if you tried to eat half a kilogram of coffee beans in one meal though. But ten grams of them make for a nice broth.


I've always vaguely assumed that there must be an evolutionary arms race going on, with prey (animal and vegetable) trying to make itself poisonous, and predators trying to come up with antidotes. Obviously, this wouldn't apply to anything that wants to get eaten (although, if they're really clever, they'll evolve to be unpleasant to anyone but the target species). So, the answer to "why isn't meat poisonous?" is "it is!".

I make no claims as to the truth or plausibility of this premise, and something feels 'off' about it, so feel free to shoot it down in flames.
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Re: What's up with avocados?

Postby thoughtfully » Thu Jan 07, 2016 10:49 am UTC

There is a thread concerning chocolate and raptors lurking around somewhere. The main problem is that the prey has to withstand a much higher concentration of toxin than the predator. Alternatively, they could keep it in a pouch attached to their belt, but clever raptors could discard the pouch before ingestion, or just lose the pouch on average, over a sufficient number of messy dismemberments :)
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Re: What's up with avocados?

Postby tomandlu » Thu Jan 07, 2016 12:03 pm UTC

thoughtfully wrote:There is a thread concerning chocolate and raptors lurking around somewhere. The main problem is that the prey has to withstand a much higher concentration of toxin than the predator. Alternatively, they could keep it in a pouch attached to their belt, but clever raptors could discard the pouch before ingestion, or just lose the pouch on average, over a sufficient number of messy dismemberments :)


Raptors - the XKCD Godwin.

"However, cats are less prone to eating chocolate since they are unable to taste sweetness."

Well, that explains a lot...
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Re: What's up with avocados?

Postby ijuin » Thu Jan 07, 2016 12:47 pm UTC

Well, there isn't much sweetness in most raw meat, and cats are pretty much exclusive carnivores--any plant matter that they deliberately consume is merely roughage that passes through unabsorbed. Thus, they have no need for a sweet tooth, since naturally sweet foods such as fruit, nectar, and sap are not important to their diets.

On the evolutionary digestive arms race thing, what surprises me is how far "ahead" humans are in the race. Our wild ancestors must have really had a lot of pressure pushing them towards becoming able to eat literally everything and anything available.

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Re: What's up with avocados?

Postby ahammel » Thu Jan 07, 2016 1:47 pm UTC

ijuin wrote:On the evolutionary digestive arms race thing, what surprises me is how far "ahead" humans are in the race. Our wild ancestors must have really had a lot of pressure pushing them towards becoming able to eat literally everything and anything available.

Maybe it's just that we're quite large animals compared to birds and cats and suchlike. You need more toxin to poison a big animal than a little one.

We've also bred the living tar out of pretty much everything we eat. It's not super surprising that it lacks human-specific toxins while the dog-specific ones are still there.
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Re: What's up with avocados?

Postby Tyndmyr » Thu Jan 07, 2016 4:53 pm UTC

That, and our ancestors were scavengers, rather than alpha predators. Granted, we are that NOW, due to technology, but evolving defences against predators seems more helpful than defenses against scavengers. Post death body disposition is usually unimportant from an evolutionary standpoint.

Plus, scavenger sorts frequently consume food that is a little off.

We kinda blur the lines in a few ways(such as with our ability to walk things to death), but it mostly makes sense.

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Re: What's up with avocados?

Postby Copper Bezel » Thu Jan 07, 2016 6:54 pm UTC

My understanding was that the arms race scenario was correct, yeah, and that animals that need a more diverse plant diet invest more energy in protecting themselves from plant toxins. So any obligate herbivore can eat all sorts of things that would kill us, and damn near any obligate carnivore will die eating something that we could eat all day, because we're still optimized for omnivory.

Edit: Knew that was ringing a bell - did we just talk about squash here? Because it was spread by megafauna too, and used to be poisonous, and apparently survived after its dispersal partner went extinct because of domestication.
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Re: What's up with avocados?

Postby Mathilda » Mon Jan 25, 2016 7:28 am UTC

They're a great base for smoothies I find. I've started drinking loads of smoothies every day to make sure I get my five a day, but I worry about the fat content of avocados.

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Re: What's up with avocados?

Postby Neil_Boekend » Mon Jan 25, 2016 10:21 am UTC

I haven't had avocado for a long time but bell peppers have lots of oil in them and they are the same plant part (seed dispersal method).
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Re: What's up with avocados?

Postby Zamfir » Mon Jan 25, 2016 10:52 am UTC

It's not really comparable - avocados have about 100 times more fat per weight as bell peppers. Avocados have a lot of energy in them, compared to any other fruit. A large avocado has in the order of 20% of the average daily energy needs - if you add avocado smoothies to your daily diet you really have to cut back on something else energetic.

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Re: What's up with avocados?

Postby KarenRei » Mon Jan 25, 2016 11:30 am UTC

There's some selection bias going on here. It may just be that people are used to seeing sugary and low fat fruits in stores because that's the sort of fruit most people prefer to consume. That said, there are even common fruits that are fatty. Coconut, for example (the white part is the endocarp; in avocado you eat the mesocarp). A lot of palm fruits are fatty, and sometimes the mesocarp. Avocado itself has a lot of fatty relatives, many of which are edible but just not common in the west. Olives and their relatives are fatty. So is durian and its relatives to some extent. And everything we call nuts, regardless of whether they're actually botanically nuts or just "culinary nuts"

I'm sure the people over at tropicalfruitforum.com could name a bunch of fatty fruits for you. Hmm, I'll go check... Okay, found a thread. Some of the fruits listed, in addition to the above (some may fall into the broader groupings I listed above, not taking the time to check):

Engkala
Uxi (Endopleura uchi)
Saifu
Ackee
Laurel family in general
Craboo/nance Byrsonima crassifolia - made into ice cream
Mauritia flexuosa - like olive
Tucuma (Astrocaryum vulgare) - so oily it's eaten like butter on bread
Acai - like avocado/olive
Buriti (M. flexuosa)
Peach palm (Bactris gasipaes) - like buttered popcorn
Dabai/tropical olive
Butterfruit (Dacryodes edulis)
Tucum (Bactris setosa)
Himalayan olive (elaeocarpus lanceifolius) - avocado-flavored. Whole genus is fatty.
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Re: What's up with avocados?

Postby Xanthir » Mon Jan 25, 2016 4:39 pm UTC

Mathilda wrote:They're a great base for smoothies I find. I've started drinking loads of smoothies every day to make sure I get my five a day, but I worry about the fat content of avocados.

Simple solution: never worry about the fat content of foods. The decades-long hate campaign against fat in your diet has extremely weak basis in reality, and the knock-on effects (us upping our sugar consumption instead, because fat is tasty and you have to do *something* to recover the taste when you remove it) are likely much worse for our overall health.

Pay attention to total calories. Fat's only downside is that it's about twice as calorie-dense as protein or carbs, so moderate your intake. As Zamfir said, eating a full avocado in your smoothie in the morning gives you a good chunk of your daily calories, so make sure you're not accidentally overeating the rest of the day.
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Re: What's up with avocados?

Postby billy joule » Mon Jan 25, 2016 10:41 pm UTC

ahammel wrote: It's not super surprising that it lacks human-specific toxins while the dog-specific ones are still there.


That's a myth according to google. The two avocado growers I know have to tie their dogs up as otherwise they eat so many avocados they become obese.

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Re: What's up with avocados?

Postby KarenRei » Mon Jan 25, 2016 11:12 pm UTC

billy joule wrote:
ahammel wrote: It's not super surprising that it lacks human-specific toxins while the dog-specific ones are still there.


That's a myth according to google. The two avocado growers I know have to tie their dogs up as otherwise they eat so many avocados they become obese.


Yep. But deadly poisonous to parrots. A number of owners have lost birds by being unaware of this fact.


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