Wednesday, October 14, 2015

Introduction to Evolution

An Intro to Evolution
Species evolve. There is no debate. There is no disagreement, at least not among those aware of facts. Yes, the mechanics of evolution are still being worked out. Does it happen slowly over time or in fits and spurts? How does epigenetics factor in? Regardless, the jury is in, ladies and gentlemen. It’s no longer a question of if evolution happens but rather how.


Resources About Evolution

Evolution works on individuals. More specifically, it works on the genome. Every organism on this planet contains massive strings composed of different iterations of the same bases—adenine, thymine, guanine, and cytosine. Together these form our DNA, a self-replicating molecule that codes for proteins, and these proteins string together into life as we know it. Some combinations are better at getting themselves replicated (unconsciously of course) and these go on to make more copies like themselves. As this process builds in complexity it is easy to mistake it as being directed or "for the good of the group." However, it does not work this way. Just as individual fish or birds can come together, each following their own set of rules to form massive schools or flocks that seem to take on complex animations, so too the individual genes within each organism function together as a whole to direct the myriad shapes, behaviors, and ecological interactions we have on this planet.
Darwin may be the most famous person in history to champion this idea of slow change over time but he most certainly was not the first. Lamarck, whose name you might be familiar with as well, believed that any trait an individual acquires during its lifetime will be passed on to its offspring. Giraffes stretched their necks to reach higher trees and therefore their offspring were born with longer necks. This has since been scoffed at for the silly idea that it is, however, advances in our understanding of things such as the immune system and epigenetics may actually give some credit to such ideas. It is an exciting time to be an evolutionary geneticist.
There was another person who, operating independently of Darwin, was developing an idea of evolution that was very similar to what we know today. His name is Alfred Russell Wallace. Unlike Darwin, Wallace was a poor man and had to schmooze his way into the right circles in pursuit of natural history. Working both in South America and Malay Archipelago and facing some devastating setbacks, Wallace converged on the idea of the mutability of species in time (evolution) in an eerily similar fashion as Darwin. As Wallace and Darwin were putting their ideas together, they found out about one another and exchanged notes. Wallace soon realized that Darwin had developed the idea much further than his own, ceded his ideas to Darwin, and by so doing gave up his spotlight in the theory of evolution. How amicable this transfer of ideas really was is a matter debate.

On a more personal level, I study plants, and nowhere is evolution more apparent. One of my favorite professors once said "When it comes to evolution, plants can do anything. Hell, you can pretty much get a new species overnight." He was being a bit facetious of course, but in a sense, he was on to something.

Life on Earth iTunes Course and Ebook

From Open Culture: Created under the direction of Pulitzer Prize-winning author and Harvard naturalist Edward O.Wilson, Life on Earth can be downloaded in 7 units on iTunes. The free book also comes with a free iTunesU course.
Learn More
All of evolution can all be boiled down to one simple question: is it adaptive or not? In evolutionary terms "adaptive" should be taken to mean a trait or suite of traits that incurs an advantage to an organism. In evolution there is no hierarchy and there is certainly no plan, so this is not a value judgment nor is it one of anything resembling choice.
This brings to mind the orchids. Quite possibly the most diverse group of plants on the planet, these marvels of evolution have captured the minds of people throughout history, and much of this fascination has to do with their bizarre floral morphologies. There seems to be no end to the variety of shapes, sizes, and colors, which gives each species its own unique look. The reason lies in the genetics of those flowers. Back when orchids were just starting to diverge, the genes for flower development were duplicated and decoupled from one another. Each new set of genes influences different sepals and petals. Because of this, orchids are able to avoid the pleiotropic effects that most other plants face and thus the sepals and petals can literally follow their own evolutionary trajectory. The result of this wacky evolutionary trajectory is the myriad orchid species we see today.
If it’s wacky evolution that you are interested in, look no further than evolution via sexual selection. In this case, organisms evolve based on the traits that are sexually appealing to the opposite sex. In most cases, sexual evolution is driven by female choice. This can be seen in the plumage of many birds. Take, for instance, the gaudy appearance of a group of birds endemic to a few islands surrounding New Guinea. Known as birds of paradise, the males of these relatives of the crow are decked out in some of the most fanciful and functionless feather adornments in all of the bird world. Colors range from yellows, to reds, to iridescent blues. Forget blending in, these males want to be seen. Their end goal in all of their puffery is to mate with a female. The females choose the males with the most outlandish adornments. Obviously, any male that can evade being eaten with all of that outlandish plumage must be fit enough to father the next generation. The result of this sexual selection are fancier and fancier males.  
You see, the genetics of an organism translate into physical and chemical reactions that, in the face of environmental pressures, either allow it to survive or doom it to death. Take, for instance, the case of rye (Secale cereale). It is easy to look at a cultivated crop of rye and assume we intentionally selected better and better varieties of this grass until we ended up with something so useful. Indeed, this is how it has gone with most plants and animals humans have domesticated. However, the case of rye may be a bit more interesting. Through a mechanism coined Vavilovian mimicry (sometimes referred to as crop mimicry), wild rye managed to escape death in ancient fields and evolve into an edible crop that now enjoys a worldwide distribution.
Wild rye (Secale montanum) was not intentionally grown for food. It was a weed in the fields of other crops like wheat and barley. Both wheat and barley are annual plants, producing their edible seeds at the end of their first growing season. Wild rye, however, is a perennial and does not produce seed until at least its second season. Therefore, most wild rye plants growing in wheat or barley fields are killed at the end of the season when the field gets tilled. However, some mutant rye plants occasionally pop up and produce seeds in their first year. Thus, it is believed that these mutant annual rye were harvested unintentionally and reseeded season after season. Over time, other traits likely developed to help push rye into the spotlight for these early farmers. Like many wild grasses, wild rye has weak spindles (the part that holds the seed to the plant). In the wild, this allows for efficient seed dispersal. On the farm, this is not a desirable trait as you end up quickly losing the seeds you want to harvest. Again, by accidently selecting for mutants that also had thicker spindles and thus held on to their seeds, farmers were unintentionally domesticating rye to parallel other cereal crops. It is believed that oats (Avena sterilis) also originated in this manner. Sure, this is a type of artificial selection, albeit unintentional, but the point remains the same.
At the core of evolution is heritable change. If it survives, there is good chance it will pass its DNA to its offspring and thus, evolution. The idea that an organism is "perfectly tuned" to its environment is a bit off. Evolution is a constant arms race. The world is constantly in flux and there has never been a time when things were static. There is no point in which the Earth could "return to" that wouldn’t be a completely arbitrary point in time. As such, life needs to constantly keep up.

Edward Wilson's "Diversity of Life" Lecture"

E.O. Wilson presents at the Nicholas School of the Environment.
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As the saying goes, diversity is the spice of life and that is very true for life on this planet. In general, the more diverse the genome, the more likely a group of individuals of a given species will be able to adapt to changes in their environment. Summers are growing drier throughout much of the globe. Whether or not any species can adapt has to do with the different codes of DNA in their cells. It is likely that at least a few individuals of a species will have the right complement to keep up following a disturbance. That is, unless we wipe most of them out. The reason our current biodiversity crisis is so scary is that we are losing the genetic insurance for the future. We don’t have to kill every last member of a species to ensure its extinction. There is a critical mass in all of this. If the genes aren’t there and a species cannot adapt to change they simply won’t.
While we are on the subject, there seems to be a lot of confusion over where we humans fit into this story. Some believe our technology has stopped our evolution. Certainly our technology has buffered us over the past few centuries. We are no longer victims of the same selection processes that plagued our nomadic ancestors. Instead, we are biding our time until hard selection rears its apocalyptic head. We are changing our environment so rapidly that very soon we won’t be able to keep up. The "civilized" world is living on borrowed time, and we are upright walking apes full of ape-like tendencies. We are brutally tribal. We wage war and drive our natural resources to near or complete extinction.
It would seem that based on ideas such as the Male Warrior Hypothesis, we are simply acting on deep seeded evolutionary anachronisms. It could very well be that our tribal inclinations and war-like tendencies are simply animalistic throwbacks to a time in which our hominid ancestors lived in a much more brutal world than we do. Alas, the major difference is that today we have drones and nukes instead of spears.
For example, modern humans exhibit a wildly overblown form of kin selection. This was useful when our ancestors banded together into small tribes that mostly consisted of family related by both mate selection as well as blood. We are a social primate after all. We are full of specialized neurons called "mirror neurons" that allow us to feel what others are feeling. In other words, they allow us to empathize. In today’s overly connected society, our tribal boundaries can become blurred and our need to empathize with others can extend further than it ever has before. Add in countless forms of superstition and an almost anti-adaptive need for glory and legacy and suddenly you have people jumping in front of bullets to save a stranger.
Our brains only ever evolved to contemplate the short term. Our abstractions of philosophy and compassion are just that, abstractions. In due time, natural selection will catch up and it will most definitely be a hard selection. Evolution has no end game. It has no end. As long as life exists on this planet, biotic and abiotic forces will continue to shape it. Life will continue to adapt. That’s how evolution works. Something will survive. The question remains whether or not we will be around long enough to adapt as well.

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