Archive for the ‘evolution’ Category

Apple of My Eye

Posted: March 29, 2011 in evolution, genetics, just for fun, plants

Next time you bite into a sweet, juicy piece of fruit, don’t let your enjoyment be diminished by the realization that you are both eating an ovary and being manipulated into playing an active role in plant sex. Ignorance might seem like bliss, but really; that plump, fleshy goodness is just as satisfying nonetheless. Kind of. Mostly. But many plants NEED animals to help them with both copulation and then also distribution of offspring, because plants can’t just get up and walk to the singles bar, nor can their children move away. So these chlorophyll-laden Casanovas devised tactics to entice unsuspecting motile creatures to do their dirty work for them. In exchange for a little sugar high, plants romance animals into carrying off feats of reproduction and migration without so much as ruffling a leaf.

Angiosperms, or flowering plants, began to dominate the planet (taking over from the Gymnosperms, which bear “naked” seeds) as insects also began to radiate into incredible abundance, diversity, and ubiquity. Coincidence, you might ask? Not so fast – with flying pollinators unabashedly doing the deed for immobile plants, these clever vegetables developed all sorts of sneaky tricks to entice the growing insect population to carry their sperm for impregnation of ova far and wide. This co-evolution gives us both the diverse beauty of the plant kingdom and the specific flower (sight, taste, smell) preferences of the animal kingdom.

I think now is a good time to discuss the difference between a fruit and a vegetable… So: All a plant’s somatic, or non-reproductive cells, make up vegetative structures. Why do we (perhaps unkindly) refer to comatose patients as existing in a “vegetative” state? Well, they’re not moving, they’re not reproducing; in fact, they are rather plant-like! On the other hand, certain structures may become specialized for reproduction – in plants, cells dedicate themselves to one or the other: normal body growth and development, OR reproduction. Flowers and their resulting fruit are such specialized tissues. Thus, any plant part NOT involved in reproduction (i.e. vegetative) is called a vegetable, while those parts directly involved in sex are called fruit. You can distinguish this by determining whether a piece of produce has seeds, which are plant embryos. Sans seeds, you have some vegetative structure from the plant. Squash? Fruit. Peppers? Fruit. Nuts? Fruit. Avocado? Fruit. Olives? Fruit. You see where I’m going with this. Seeds = Fruit. Beans and peas ARE the seeds! (The pod is the fruit.) This defies the conventional wisdom of amateur chefs around the globe. Consistently, we call items traditionally seasoned with savory flavors “vegetables” while reserving “fruit” for items incorporated in sweet dishes. You may want to take a moment to reflect and recoup after that reality-altering realization.

When it’s time for an angiosperm to have sex, the plant diverts energy and nutrients into creating differentiated reproductive structures. Leaf and other tissues specialize into distinct flower components by altering gene expression and up-regulating exactly those genes necessary for each cell’s particular role. A flower often has female parts – collectively called the carpel, and male parts – comprising the stamen. On the anthers (tips) of the stamen, pollen grains are hollow structures housing millions of individual male gametes (sperm!). Insects pick up these grains and transport them to the carpel of a different plant. Flowers, then, share a bit of nectar in exchange for fertilization!You know that bulbous structure at the base of flowers? Within that ovary lies the ova, or eggs, of the flower. When a bee brings foreign sperm into contact with a viable egg, the receptive flower begins to produce ethylene gas, which triggers the decline of any flower parts not essential in seed and fruit formation (this is the same compound that causes ripening of fruit). Simultaneously, the receptacle and/or ovary wall tissue grows, swelling in size to form a protective (and often tasty!) structure in which to house the developing offspring. Eventually, the structure begins to look like a fruit as we know it; the seeds are the embryos (or house the embryos).

When trees establish themselves in the ground, they compete with one another for resources; access to sunlight, and surface area to absorb water and nutrients from the soil. Mature trees then will often be found spaced apart, at whatever distance that particular ecosystem has the nutrients to support them. So to prevent the parent tree from competing for valuable resources with offspring, trees would like to be able to distance themselves from their seedlings…..And so: The fruit was born. When you or I or some other creature comes along and spies a shiny treat dangling tantalizingly from the tree, we promptly grab it and go. In doing so, we are feeding right in to the plant’s plot – As we wolf down the sweet snack we inadvertently consume the seeds (or, for picky humans, toss them far from the parent plant). Fruit, then, share a bit of nutrition in exchange for seed dispersal (where do you think the term “spreading his seeds” comes from?!).

Intact seeds pass through our digestive system without great harm to the protected embryo. It’s no coincidence that fruits contain fiber and other compounds that aid in excretion; in fact, many fruits contain natural laxatives that induce peristalsis (smooth muscle contraction in your digestive tract) and literally force expulsion of the seedlings. This is pure plant genius. Not only have you safely carried (dispersed) the angiosperm offspring to a new location, you have planted it happily within a cushy pile of fresh, hydrated fertilizer. What more could a germinating baby plant ask for??

Incidentally, it isn’t only plants who have evolved these sneaky tactics – fungi do their fair share of animal manipulation as well. After all, what is the stereotypical place to find ‘shrooms? All’s fair in love and war. And love is war.

The Secret Recipe

Posted: February 26, 2011 in biochemistry, evolution, genetics

I am guilty, along with countless texts, websites, experts, and novices, of an academic travesty – using an inaccurate simile to explain scientific phenomena. Namely, the description of genomic information as a blueprint and the body as the resultant structure.

Thank goodness I recently failed to notice The Agile Gene was merely a renaming of Nature Via Nurture, and was therefore conned into reading it again. It reminded me of what I already knew, but lie buried beneath the weight of my formal education… Our DNA is not a blueprint but a recipe. We are not built, but baked.

The building designed from a blueprint is literally the sum of its parts. A cake, however, or a human, is a whole greater than its sum; it takes on properties not obvious from the list of ingredients. What, asks Blumberg in Body Heat, is the essence of a chocolate cake? Is it the eggs? Flour? Cocoa? No, these are merely ingredients. Nor is it the pan, oven, or whisk. A recipe is clearly not a cake, either. What is the essence of a human? How can it be captured?

The reality is that simply unraveling our DNA does not explain how it works, any more than knowing the alphabet helps you to read a book (with apologizes to Charles Arthur).

It seems we expect too much of our limited understanding of DNA, which derives from the metaphors we use about it. When we can only describe something indirectly, it may falsely acquire the expectations realistic of the associated analogy. We therefore look to genes to solve riddles, fix problems, and explain mysteries. However, we forget that it just isn’t so simple…

Consider what the greatly missed writer Douglas Adams pointed out – Imagine that you were trying to describe how to make a fruit cake by writing the blueprint: currant here, surrounded by certain amount of air-filled cake mixture, and then more currants. It would be hellish. So how do we make fruit cakes? Not by blueprint. We use recipes – mix these things together, bake at a particular temperature for so long, and voila: if you’ve got the components right, you’ll have currants distributed satisfactorily around your finished product.

Think about it: Bakers use, by and large, the same ingredients in many recipes to produce a wide variety of unique confections. The art of baking lies in the ratio of flour to sugar to eggs to salt, and such; not in using different ingredients for each different recipe. Can you predict the precise structure, placement of parts, consistency, etc. of the product just by looking at a recipe? Nope.

Likewise, many organisms share many genes, probably from a common ancestor. We change around the timing, intensity, and location of gene expression, throw in a few special touches, and viola! become unique individuals. But it isn’t just genes that make us who we are – environment clearly affects the expression of genes.

Okay, so you’ve made the cake batter or bread dough or what have you – now what? The oven condition and quality, local elevation, humidity, etc. all have significant impacts on the final product. Some cooks create masterpieces at low temperatures for a long time; others dazzle with short durations of high heat.

The secret ingredient we’re often missing when we describe our genes as a blueprint is quite possibly that elusive fourth dimension, forgotten usually by its continuous presence – time. You can break a structure back down into its constituent components; you cannot unbake a cake. Or a person.

One of my favorite analogies used by Ridley is: You and I and other animals share the genes necessary to make vertebrae. This neck sauce, as he calls it, is used to marinate giraffes for a much longer time during their development than us people; yet we too were briefly soaked in that sauce. Snakes are basted in the marinade during their entire development and thus end up with a neck the length of their body! But each of us express the same neck genes in our neck region; the difference is how long, and how much marinade we soaked in as we developed. You see, we were not assembled, we were concocted.

If something disrupts our proper development, or throws off the timing of gene expression, then that something has the potential to cause disorders and disabilities. We are the products of the conditions in which our genes are expressed; not only that, but the conditions we find ourselves in further influence future directions of gene expression.

As the psychologist Gary Marcus has pointed out in yet another attempt at an applicable analogy by which to understand something not quite understandable, genes function like IF-THEN lines of code in a computer program. The IF refers to the regulatory portion of the gene and THEN refers to the protein template region.