Evolutionary Anachronisms

The avocado.

You may think you have a good relationship with the avocado. The buttery fruit of this plant may regularly accompany your turkey sandwich, sliced and fanned out across the bread. Or, it may serve as a hearty dip in the form of guacamole. More recently, avocado is seemingly being utilized in a greater variety of ways, being deep-fried, thrown in macaroni and cheese, and finding its way onto burgers, Subway sandwiches, and even into ice cream. You’d expect that with all this attention, our green-fleshed, knobby-skinned friend, the avocado, would be content with its current role in human culinary efforts.

However, the avocado may very well be lonely.

Despite all our affection, this loneliness stems from the avocado potentially having eyes for another. I mean this, of course, in the sense of the concept of co-evolution (which I examined in a previous post), which is directly tied to the reproductive role of the fruit itself. The main function of a fruit (a botanical fruit, typically meaning the structure derived from the reproductive tissues of the flower housing the seed(s)), is to move seeds away from the parent plant and into areas that promote growth and survival. Many types of adaptations in fruits exist to help achieve this goal of seed dispersal; from the wind-catching dual blades of maple tree fruits (known as samara), to exploiting the appetites of the ubiquitous (and notably mobile) animals in the neighborhood. This latter evolutionary strategy involves the development of fruits that enrapture animal taste buds and provide irresistible caloric value, allowing consumed seeds to travel safely inside the gut of an unwitting, far-traveling chauffeur until being excreted away from the crippling shade of the parent plant. This is called “endozoochory.”

Most endozoochorous fruits have evolved to be eaten by fairly specific animals. Predictably, fruits adapted to be taken by songbirds are going to have different physical attributes than those associated with insects or elephants. You can try and fit a peach pit through the body of a sparrow, but you aren’t going to get very far. Similarly, expecting tiny, thin-walled seeds to withstand an elephant’s battery of grinding teeth isn’t realistic either. The suite of fruit traits evolved for dispersal by a given group of animals roughly categorize into “seed dispersal syndromes.” By interpreting these syndromes, we can often get a good idea of what the primary dispersing animal, the other partner in a co-evolved relationship, is likely to be.

In light of this, it becomes obvious that despite our love of the avocado (specifically, domesticated cultivars with lots of flesh; wild avocado fruits have a thinner layer of green deliciousness surrounding that pit), it is not “meant” for human consumption and seed dispersal. Any attempt to chew up the whole fruit and swallow the massive pit is bound to land your asphyxiating ass in the cemetery. However, the situation for avocado’s seed dispersal isn’t much better in its wild Neotropical range. Many smaller animals (like monkeys) that partake in avocado consumption are “pulp thieves”, ingesting the oily layer and tossing the seed at the base of the parent tree. In fact, no native animal is known to consistently and effectively disperse wild avocado. Why then does the avocado make a big, energetically expensive fruit that doesn’t cut the mustard on dispersal? Also, who is the true “buyer” of avocado’s product?

The answer to both those questions may be that the avocado’s chief dispersal agent is extinct. Kaput. Gone. Effectively an “ex-animal.” This would mean that the avocado fruit is an evolutionary anachronism, equipped with traits fine-tuned by evolution for interaction with a species that has quite suddenly disappeared, leaving the once perfectly capable seed vessel under-appreciated and inadequately used.

“Fruit’s almost ripe, guys. Come and get it! Hello? ….Guys?!”

It’s a very serious case of being all dressed up with nowhere to go.

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Metatherians (Part 1 of 2): Extinct Megafauna

Marsupials.

The immediate association most people have with the term ‘marsupial’ is that of fantastical, adorable, fluffy beasts in the far-away magical land of Oz, equipped with built-in fanny packs for storing their tiny, even more adorable, offspring. Bounding, big-eared kangaroos, sleepy koalas, and perhaps a hyperactive sugar glider or a waddling opossum might cross their minds. Not too far beyond this is where the train of thought pulls into its final stop, and suddenly they’re caught up in the romanticism of Australia itself; the sun-baked, tawny Outback scabland, didgeridoo droning in their mind’s ear, impossibly colorful fish flitting about the Great Barrier Reef, and perhaps Hugh Jackman or Nicole Kidman (whatever their fancy) driving cattle across the Northern Territory during The Dry.

While this idealization is all well and good, there is actually a lot more to these pouched animals than what fits on the in-fold of a Qantas brochure.
Marsupials are really bizarre by mammalian standards, and have a rich and relatively unrecognized evolutionary history that spans back 125 million years. This entry is one of two that will be devoted to these weird little creatures, focusing first on their unrealized illustrious past, and then on lesser known representatives of their clan in the present.

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Dragons

Dragons.

We’ve known them as ancient, mythical, winged, pyromaniacal reptilian beasts with a flair for the dramatic and destructive. They have been a fixture in our lore, in some form or another, the world over. While most of these tales of dragons are fictional, or at least highly embellished, there is still a very strong chord of truth in them. The blaze-setting, screeching hell-drakes so common in storybooks have not existed for a very long time, and it is unlikely that Medieval humans actually had contact with them (this stands in contrast with unicorns, which went extinct in 1982 when the last specimen escaped from her enclosure and ingested some antifreeze). However, dragons have had a rich and colorful evolutionary history that dates back 225 million years, and their unique biology and rise and fall in biodiversity is worth discussing.

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Flightlessness

Flight.

Powered flight (in the biological world, flight that comes from the mechanical flapping of wings as opposed to passive drifting or gliding) can be found in a wide range of animals on our planet. It is has evolved independently in insects multiple times, leading to a biologically diverse menagerie of colorful blotches on our windshields. While insects are far and away the first creatures to master the air (by a solid 200 million years), and the only invertebrates to do so, they share the skies with the much larger vertebrate fliers like birds, bats, and at one time, the reptilian pterosaurs. Aerial locomotion provides an animal with obvious advantages; ease in avoiding predators, access to new habitats and food sources, and the nullification of the game of Monkey in the Middle. There definitely are interesting correlations concerning the success of flying; it appears as though once evolved, flight is an incredibly successful strategy. Bats account for a fifth of all mammal species, birds have the most species of any land-lubbing vertebrate class, and the class containing insects is more speciose than all other animal groups combined. So it obviously pays to take to the skies, on a numbers and diversity level. That, and flying is quite clearly the most badass way to get around.

And yet, some representatives of these flying lineages drop the practice altogether. One explanation is that they are ungrateful, arrogant pricks who wouldn’t know the value of an honest day’s wingbeat if it bit them in the ass.

“Soaring elegantly through the heavens is sooooo mainstream.”

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