Evolution for Dummies

This post shall serve as a crash course in evolutionary theory. Since so many people don't seem to (or don't want to) understand evolution, I figured it was time for a refresher. Many of these sections will eventually become part of a lecture I hope to start giving at the Alaska Museum of Natural History, where the turnout is usually terrible, but people actually come to learn, not criticize (what a novel concept!). The picture above is from Bininda-Emonds, et al. (2006) paper about the delayed rise of present-day mammals, and it's a darn good visual aid. While I've never really liked circular phylogeny trees, this one works pretty well thanks to its strategic use of color. If I'm not clarifying anything, let me know, and I'll work to improve it. My goal is to have people walk away with a full (if simplified) understanding of the evolutionary process, some easy examples showing why it works, and a greater appreciation for the science behind it. Now then, without further ado:

Change is Good

Evolution is not a difficult concept. In its simplest terms, evolution is the survival of those best suited for their environments. You may have heard it referred to as "survival of the fittest," but the word "fittest" is a bit misleading. "Fit," in this context refers to an organism's ability to survive in its environment, find food, and breed. In the end, Mother Nature is the ultimate judge and jury for any given species, demanding that we change or die along with the environment that spawned us. Put a polar bear in the savannah and it will quickly die. Put a lion in the Arctic and it will quickly freeze. Each animal on the planet is superbly adapted to deal with the challenges faced by its surroundings. In short, the environment shapes the flora and fauna that live in it.
The first thing I should make clear is that evolutionary theory is not concerned with how life arose. Whether the first sparks of life appeared in deep sea vents, on Mars, in lava beds, or on the surface of cave pools, that is not what's important. Ultimately, evolutionary theory seeks only to explain the processes by which life took off from that point. If you want an answer to how life arose, you should seek out a biochemist, astronomer, or, perhaps, religion. What I can tell you, with some certainty, is that life did not come from rocks. How organic life can be connected to sedimentary processes, I have yet to discover, and it is not a theory that anybody in the scientific community is suggesting. Yet from the time life first appeared on our little blue planet, almost 4 billion years ago, that life has been changing. If life had not changed and adapted to the changing environmental conditions facing it at every turn, we would not be here today.

Imagine that you are a tree shrew. A tiny, seemingly insignificant rodent that makes its living mindlessly running from tree to tree trying to find food and avoid being eaten by a bird. Your brothers and sisters are in the exact same predicament, of course, but you are special somehow. Your first finger is in a kind of reversed position. This means absolutely nothing to you, of course. Rather than study the construction of your palm, you'd rather run from that big shadow that just passed overhead. There are bugs that need to be eaten. And yet, you find yourself able to climb the tree faster and more adeptly than your cousins. You can cling to branches that your siblings would fall from. You agility in the canopy has ensured you an almost limitless foraging ground that is virtually unreachable by your family below. When it is time to breed, you find a willing little female, and in time, she produces a large litter. Some of these babies have their father's bizarre, yet somehow improved, thumb.

The babies grow up, doing basically what their parents did, and they have babies. The wierd thumb gene is passed on again, and the number of wierd-thumbed individuals increases with each passing generation. The shrews with wierd thumbs increasingly find themselves in each other's company. After all, only they can reach the upper levels of the trees, and this is an advantage that they take advantage of. At some point, a male and a female wierd-thumbed tree shrew mate, and the vast majority of their pups also have wierd thumbs. Eventually, two distinct populations of tree shrews become visible: The "original" crop stays on the tree trunks and lower branches, while a new batch can be seen leaping and cavorting around the canopy.
Ladies and gentlemen, that is how the process works. It could not be simpler. In fact, that example was perhaps too simple. Let me give you another one, that may strike a bit closer to home.

Upright? Alright!

Now imagine that you are a chimpanzee who lives in the jungle. You and your family have lived in the jungle for generations, of course, and you have never known a better life. Your family is a member of a large troops of chimps, and you notice that one of the younger males has a strange posture. He habitually walks upright, moreso than his siblings or parents. He has an awkward bow-legged gait about him, but otherwise seems quite comfortable wandering on two legs. Around the same time, you begin to notice that the boarders of your jungle turf are starting to close in on you. The weather has been terribly hot the past few years, and drier, too. Looking out beyond the boarders of the jungle reveals a frightening new landscape, alien to you and your family: grass. Nothing but tall, tan grass. The scorching sun beckons overhead, but you do not dare go out into that scary place. From your perch among the trees, you notice a host of huge creatures out there. Big elephant-like monsters and something that looks like a leopard, except larger, and with bigger teeth. Much bigger.

When on the ground, you cannot see over the top of the grass, and yet your boarders are becoming smaller by the day, it seems. From the treetops, you can see the encroaching grasslands impede upon other sections of the jungle, as if the tan blades are intent on overtaking the entire region. That strange chimp, however, wanders in and out of the grass with some regularity, often returning with strange vegetables and strange animals he killed. You realize that he can see over the grass, at least when walking on two legs, and has found a bounty of unrealized foodstuff. Other members of your troop often sometimes leave the jungle to try and replicate his results, but they do not often return.
After many years, the male becomes the leader of the troops, winning favor from all of the females with his bounty of food. His children also walk upright, and they watch their father take trips into the mysterious grasslands. They eventually follow behind him, where they meet other chimps from other parts of the sparce jungle regions who have the same adaptations as they do, both male and female. The cruel Earth punishes the members of his family who are unable or unwilling to keep up or watch the horizen, as saber-tooth cats and giant elephants brutally slay the lazy or foolish. By their loss, the overall upright chimp gene pool is strengthened, and eventually a new population of savannah chimps emerges. Like the tree shrews, two chimp populations are now apparent: the old jungle-dwellers and the new grassland chimps.

So it bothers me when people ask, "If humans evolved from chimps, why are there still chimps?" This attitude demonstrates a basic lack of knowledge regarding taxonomy and population dymanics. Just the other day, somebody (I forget who) asked me, "How did dinosaurs evolve into birds? Triceratops doesn't look anything like a bird."

Non-Avian Ceratopsians

The new always branches off from the old. The new never completely replaces the old. In the tree shrew example, as well as the chimp one, notice that the "new" species comes from the original stock, and only a small portion of the original stock. Not every chimp in the world suddenly turned into Australopithicus. Rather, in a single place in Africa, among a single troop of chimpanzees, a few individuals began exploring the grasslands. The other 99% of the chimps stayed in the jungles, content to keep doing what they'd been doing. In the Triceratops question, realize that saying "dinosaur" is like saying "placental mammals." There are a lot of dinosaurs, and only one twig (Paraves) of one branch (Maniraptora) of one stem (Theropoda) of the entire Dinosauria figured out how to fly.

Not all dinosaurs evolved into birds. Only paravians did. Not all chimpanzees evolved into hominids. It was probably an isolated event among a single population. But in all cases, the old group does not simply disappear--they keep doing what they always did.

So in this sense, every animal (and plant) on Earth is both a transitional form and a terminal taxon. Every kind of living creature comes from a pre-existing kind of living creature, yet the old will always remain, and is specially adapted to its environment. Every animal has the potential to produce a new species, yet every animal is tied to its environment in its own way.
Notice that, in the chimpanzee example, the upright chimps who begin exploring the grasslands meet others like them. I say this to illustrate another often-overlooked facet of evolutionary theory: mutation rates. The old Darwinian model suggested that mutation just happens over time, and until those mutations occur, the genetic pool is stable. That is simply not the case. When Eldridge and Gould were coming up with punctutated equilibrium, and then genetics came to the forefront of evolutionary research, scientists quickly realized that genetic mutations are constant among populations. I'll give you an example:

I have Cystic Fibrosis (no, really). I am one of thousands of people with CF, yet CF is most prevalent among those of European decent. Why? Because CF protects against cholera, and cholera outbreaks were fairly common in medieval Europe. Now, you don't actually have to have CF to be immune to the drying effects of cholera. Rather, you need only have a specific point mutation of the CFTR gene, which causes your cells to retain fluid (malfunctioning chloride channels). CF is the result of two people with CFTR gene mutations getting together and having a kid, at which point there is a 25% chance (the CFTR gene is a recessive mutation) that kid will get BOTH faulty copies of the CFTR gene, one copy from dad, and one from mom.
Now, when cholera was blowing through medieval Europe, people were dropping like flies in the streets (or, you know, in their homes). The CFTR mutation was not widespread by familial ties alone, rather it sprang up independantly in multiple places and families around the continent. Mutation occurs at a constant rate in a population, and certain mutations are, supposedly, always apparent in some percentage. The CFTR mutation remained hidden, however, because it gave its owner no real benefit...until cholera started sweeping the land. Only then, when the environment significantly changed, did the CFTR carriers suddenly have an advantage.

So when the grass started overtaking the jungle, the chimps who walked a bit upright would have suddenly had an advantage over their peers that was not apparent before. Supposedly, there are always a very small percentage of chimps in the world with a slightly upright posture. Why don't they become australopithicines? Because the environment does not demand it. Until the environmental conditions of the Miocene era repeat themselves, the slightly upright chimps have no visible advantage over their peers. Just like on Heroes, there are mutations even among our own species, but those traits are not advantageous until the environment justifies their presence.

Another assumption that always bothers me is that old Lamarcian notion that the giraffe woke up one morning and decided it was going to evolve a longer neck. That's not how it works. No animal pines to be another animal. But when the mutations we've discussed above allow an animal to take advantage of resources its peers are unable to, then its unique mutation will be passed around, and the mutation will spread. The ancestor of giraffes did not want to eat those succulent greens, but one day there was a giraffoid born with longer legs than its brothers and sister. Its feeding range was higher, and it was able to snack on a bunch of food that its siblings and family were not. The giraffoid wasn't aware of this change--it was just doing what came natural, as the phrase may be.

Lance Armstrong was born with an abnormally large heart, which I'm sure conferred upon him some measure of cycling success (not that hard work, intense training, and sheer manliness didn't help). If Lance Armstrong lived in a more primitive time, where aerobic endurance actually meant something, he would probably outrun other members of his tribe, who would have been eaten by wolves. Thus, he would've gotten first choice when it came time for baby-makin'. And that big heart would have been passed on to some of his kids.

So a Smilodon and a Thylacoleo Walk Into a Bar...

What about convergent evolution? Convergent evolution is where two unrelated animals develop the same trait to deal with similar environmental conditions. A great example of this is Effigia, a small crocodilian that developed a toothless beak, bipedal posture, and a handful of other advanced dinosaurian features independantly of dinosaurs. Creationists would say "It's just a dinosaur, see?" But it's not. It's an example of convergence, and convergence is one of the more difficul things to understand about evolutionary theory.

One could even argue, based on where it was found and when it lived (and who its neighbors were), that Effigia is a dinosaur-mimic. We see mimics all the time in nature: Caterpillars that mimic snake heads, snapping turtle tongues that mimics earthworms, butterfly wings that mimics eyes, insects that mimics plants. When it's breezy outside, my pet chameleon sucks his gut in, stands on his back legs, and wobbles back and forth, trying desperately to look like a leaf (I'm not sure who he's trying to fool)! Perhaps Effigia's ancestors were being gobbled up by Coelophysis, but the freaks who were wandering around on two legs were fooling their attackers into thinking the little Effigias were baby theropods. You never know. Maybe Effigia's ancestors were finding food or escaping predation easier on two legs.

Here's an easy example of convergence: sharks, dolphins, and ichthyosaurs. They all have the same general body plan: dorsal fin, large pectoral fins, fluked tail, big eyes, torpedo-shaped body. It's tough to say that sharks and dolphins are both "just sharks" or "just dolphins." The two are clearly different. Likewise, ichthyosaurs seem to be related to lizards, so despite their preference for live birth, ichthyosaurs are clearly reptiles. The trick is that an oceanic lifestyle, especially if you're a hunter, requires a certain bauplan. The slick, torpedo shape is streamlined and is resistant to drag. This adaptation is easy to envision--ancient sharks, dolphins, and ichthyosaurs with more streamlined shapes were able to move better in the murky depths, thus ensuring a plentiful bounty of food. In all three animals, a tail fluke developed as the bony part of the tail bent sharply downward at its end, and a cartiligenous spur emerged at the bend, supporting a fleshy fin.

This allowed each animal to propel itself through the water--certainly an important adaptation. It should be noted that a tail fluke is not the only way to go. Mosasaurs, which propelled themselves primarily with their tails, adopted a flat, crocodilian tail surrounded by a fleshy "fin," enlarging the tail's surface area. Take a look at a sea snake's tail for a modern example of a mosasaur tail. Anyway, sharks, dolphins, and ichthyosaurs also developed a dorsal fin, which further streamlines the body and, in dolphins at least, serves as a display structure.

It is in the forefins that each animal found a different means around the same problem. In sharks, the forefin is made up of straight cartilage spikes encased in a heavy mitten of meat and scale. Sharks do not have wrists or elbows, but only shoulders. The dolphin shortened its arms considerably, retaining an immobile shoulder and wrist, but grew each finger out, like those of a bat, and encased the whole structure in a fleshy mitten. Ichthyosaurs shortened their arms, but increased the number of fingers and individual finger bones. Ichthyosaur hands are made up of a huge mosaic of tiny, rectangular bones that have barely any resemblance to the ancestral tetrapod condition. Look at the picture above! It's hand is basically a solid paddle! But you can see that all three creatures developed certain traits because the environment shapes the animals and plants that live in it.

Humans and the New Environment

Some animals adapt by not adapting their physiology, but only their behavior. "Pest" species are great at this. They take advantage of, namely, humans. Not long ago, pigeons, ravens, and crows all realized that humans leave a lot of waste around, and waste is yummy. New York City has an infamous rat problem, because rats breed quickly and can eat just about anything. In the nutrient-packed human cities, rats and their relatives are becoming the kings. Here in Alaska, bears and moose have quickly adapted to city life, munching on refuse or gardens left behind by people. Sadly, this often results in confrontations between the big mammals and people, and those confrontations usually result in the death of a bear or a moose. Even wolves, those perpetually xenophobic predators of the Alaskan North, have been coming closer and closer toward the city limits in recent years. There have been several sighting by our airport. Wolves are just now learning what bears have known for decades: Trash is free, and people throw out a lot of food! Unfortunately, while some animals are able to generalize their behavior quite well and fit into our modern city life, others are not so lucky. Amphibians and reptiles, especially, are suseptable to pollution and environmental degredation. You can't drive half a mile along a midwestern highway without seeing at least one good-sized mammal or turtle squashed in the road. Sadly, animals that are adapted for a specific environment or behavior are in the most danger from our quickly expanding cityscapes and populations. How does the concept of "change or die" fit into a world that changes quicker than animals can reproduce or survive to find a mate in the first place? Humans have irrevocably changed the face of evolutionary dynamics, and many, many animal and plant species are paying the price.

Above the Natural Law

Tragic though that may be, one of the most interesting aspects of human impact on evolutionary dynamics is that humans now control their own evolution. Whereas mother nature once determined who lived or died, we have gained the incredible ability to shape our own world. Are people being eaten by lions in a village in Africa? Guns, disease, and deforestation should take care of those pesky carnivores. In so many cases, it is the strong that are not surviving, as literacy and education rates have a direct impact on child-rearing. The more educated you are, and the wealthier you are, the less likely you are to have children. But the opposite is also true--the dumbest and poorest among us are the ones passing their genes on. It's actually the complete reverse of natural evolutionary theory--it is the survival of the least fit among humans, and thanks to modern medicine and a host of social and political influences, those children will surely reach sexual maturity and have kids of their own, and the weak shall inheret the Earth.

Humans have forever changed how the game is played, and we must be aware of that. How can we understand how we are changing the world if we do not have the capacity or desire to understand how natural processes work? You can't change what you don't understand, and sadly, that is a prevalent way of thinking in our short-sighted and greedy human society.

Any Questions?

Thus endeth what has become one of the longest posts in When Pigs Fly history. Please, if you have any questions, concerns, or would like to see parts of this lecture fleshed out more, let me know. Also, tell me what you think! I'm considering adding a section on symbiotic relationships, especially between flowers and various animals. And expect another enormous post soon, regarding the History of Feathered Dinosaurs! I may also add to this post in the near future, as I re-read it and find things that need changing or places that need adding-to.