Thursday, October 04, 2007

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.


Julia said...

I'll have a look at this over the weekend. :-)

Will Baird said...

Hey Zach,

Not bad. You're going to need to redo the human evolution bit. Chimps and humans are derived from a common ancestor. Chimps and humans are VERY derived wrt that ancestors. Humans are NOT derived from chimps. Please work that in somehow. You don't have leftovers all over the place. You have different populations that each continue to evolve: frex, again, Chimps. knuckle walking is derived. bipdealism, iirc, is basal.

Zach Miller said...

I know that. I was just trying to make it easy to understand, and writing "ancestral hominid" gets old pretty quickly. Thanks for the comments!

Amanda said...

Cool...this was nice to read...have you read Jack Horner's Digging Dinosaurs? This reminds me of that...there's science there, but it's conversational. Loved that book.

Erik said...

You knew I couldn't just let this slide. So here goes.

Survival of the fittest, completely agree. Small adaptations are what keep species from dying off instantly. Adapt or die is basically the rule for animals. Correct?
This is what I'd like to call micro-evolution. It's observable, and has been proven by the scientific method.

However it takes a leap of logic, some would say a leap of faith, to believe these small adaptations cause change from single celled organisms to extremely complex multi-cellular organisms.

Your examples are all examples of micro-evolution. The tree shrew for example, you start out with a shrew, and end with, get this, a tree shrew. It still eats bugs, it still runs from shadows, it still has a life span of a few months. Not only did you not get a new kind of animal (say a monkey), the only change is a strange configuration of toes.

Even then, what are the odds for a beneficial mutation like that? Astronomical! Probably the little guy would have a lot of pain in his toes, because they were deformed, which would slow him down and make him easy prey. Take baby gecko for example, his elbows were backwards, did that help him any?! I think not. Also females would be less likely to choose him as a mate because of his deformity; things that stand out from the norm are very rarely accepted by the group.

Your second example, you start with a chimp, excuse me, ancestral hominid, and end up with an ancestral hominid with a penchant for a slower gait which not only is less efficient but taking an upright stance exposes it to sharp eyed predators who can also see above the grass. This would also limit the tree climbing ability of your beloved upright walking tree goers.

To go from tree going forest dwellers to upright plains dwellers a major change in the hips form and function would have to take place, something that would not happen easily, and in between the fully tree going, to the fully upright walking groups would be a form of ancestral hominids that were good at neither. Making them easy prey, they would not be the fittest, so they would not live. Correct?

The rest of it, I don’t even want to get into right now. But if you could clarify this it would help:

“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.”

I disagree. I can change what I don’t understand. I can even change what I don’t realize exists! Besides, why shouldn’t I be short sighted and greedy? Aren’t I just trying to pass my genes along? Isn’t success of the species the most important thing? Given the evolutionistic world view, we’re all just animals trying to survive as best we can correct? Survival of the fittest!

I’m just curious how our mental prowess fits into your model here. What does it matter how we define the world around us? Relationships of long-gone species truly do not matter in the long run. The earth will eventually be destroyed by our sun, so why worry now about the other animals on our planet?

Our species will eventually die out anyway, so what is the point of making sound decisions now? How can this amazing intellect of ours help us avoid the inevitable? Where does evolution go from here? I realize evolution doesn’t cover questions like these. Evolution has nothing to do with what’s important, but I wouldn’t mind getting some feedback through personal opinion.

Alright. I’m done.

Zach Miller said...

Erik, you get a new species the second the two groups can no longer interbreed. And the whole point of the shrew example was to show how the process gets started. How do you know he would've been horribly deformed by his thumbs? I doubt females are paying much attention to his thumbs. Also, I saw a guy once who only had three fingers (he worked at Carrs!). He didn't seem to be in all sorts of pain to ME.

And with the chimp, maybe he's just as good at walking upright as he is on all fours. He's wandering around the grasslands, picking up tubers and whatnot, but when he sees the grass start to move in the distance, he drops onto his knuckles and sprints back to the jungle. I don't know. These examples aren't set in stone--they're just there to make people understand the process!

And evolution IS a matter of micro changes. A mother paravian didn't lay a bunch of eggs and one of them turned out to be Archaeopteryx. Because one change takes place (thumbs in the tree shrew), others come from that, because the thumbs open up ONE new niche, but that new niche involves a new set of challenges. Maybe there are fewer bugs and more fruit up in the trees, so the shrews who have "mutant" dentition survive better than those with insectivorous dentition.
And then maybe, because fruit is such a big thing now, shrews with color vision (at least weak color vision) are able to see more kinds of fruit than those with ancestral B&W vision. And then maybe the little buggers find that a prehensile TOE gets the climbing job done even better. And then, because vision is such a big deal in the high trees, eating fruit and all, we find that the shrews with more forward-facing vision survive at a higher rate than those without.

You see? In just a few short mutations (granted, it takes a few thousand if not million years), we've gone from shrew to primate. Monkeys have forward-facing vision, heterodont dention (but they mainly snack on veggies), prehensile thumbs and big toes, color vision, and some have prehensile tails.

It's just not that tough. It's a series of changes in the anatomy, and it's all about how you DEFINE the new animal. A monkey is a shrew, Erik. It's just a weird tree-loving shrew.

As for our massive brains, yes, they are the result of natural selection too, but I don't think that gives us eminent domain over the entire planet.

Scott said...


Zach has omitted much for the sake of clarity, but I'm going reinsert a few key concepts here. Hopefully, they'll help you understand a little better.

For starters, evolution does not really happen to individuals, but to populations of individuals. What this means is that the example shrewmorph in Zach's example possesses a variation within a larger population.

Are the odds against this astronomical? Hardly. Many members of his species have the toe opposition mutation. If they favor foraging in the canopy, they may also favor living there, and living there, loving and having lots of little weird babies there as well, thus ensuring the mutation becomes increasingly concentrated within that population.

Those without the variation might well remain on the ground or even go underground.

So it's not just a change in the toes; it leads to a change in lifestyle, which can separate two species by splitting them in two. If enough geographic and morphologic drift is allowed, over time, one or the other group will become reproductively isolated.

It's putting the cart before the horse to object that the odds of a beneficial mutation Zach describes are unlikely. The mutation is not passed along because of an unlikely chain of events per se, but because the benefit was played out over time with an already viable, breeding population. Calling it unlikely is therefore silly.

So where did the varations come from? Where all variations come from: they come from sex.

When your parents DNA was combined, you inheirited traits from both. Some were recessive, and were pushed back in the expression queue, and others were dominant, and were expressed when your DNA was read back.

The combination of dominant and recessive genes dictates which genes are expressed--but even so, you will still likely pass along that combination to your kids:

Mother's got Rr (r represents our little weird mutation)
Father's got RR

Is there little chance r will appear in their offspring? Hm:

R r

50% doesn't seem that unlikely to me.

Let's add a generation:

Mother's got Rr
Father's got Rr

R r
r Rr rr

The double-r has now a 25% chance of appearing.

If you have lots of kids, the likelihood of all of these combinations appearing increases substantially.

Of course, genes change over time, sometimes dramatically (in the case of chromosomal duplication), or subtly (single base-pair reproduction errors). When that happens, new information is introduced into the genome.

Now keep in mind that it's not just happening to a single individual, but to everyone within that breeding population.

If that population is large, selective pressure is not only likely to affect which genotypes are expressed over others, but it becomes actually inevitable.

If it were truly unlikely, it should be easily stopped. How would you keep a population of 100,000 or so shrewmorphs from breeding?

Scott said...

"Isn’t success of the species the most important thing?"

Generally, no. The most important thing is that your genes get passed on.

Species is only a useful term to describe an interbreeding population of individuals.

Erik said...

Scott, please listen to what I say. I’ll quote myself here. “Survival of the fittest, completely agree. Small adaptations are what keep species from dying off instantly.” I agree there is change within populations. What I’m saying is the odds against a mutation that gives a substantial advantage are terrible.

Correct me if I’m wrong here but, dominant genes are slowly ousting the recessive genes right? In humans brown eyes are beating out blue, slowly. One day everyone will be brown eyed. Such is my limited understanding of genetics. This leads me to believe populations are losing genetic diversity, not gaining it. In fact a population would have to be isolated beyond natural processes.

Zach thank you for clarifying the point, although you know that I know exactly what is stipulated by evolution as it is presented, here’s a quick and easy question. Has speciation been observed in the natural world? If yes, my next question would be, are they truly incompatible? Meaning genetically could they simply not breed? Meaning no living offspring.

Rather not get into a huge debate, only one point I’m trying to make here.
1. Macro-evolution has never been, nor ever will be observable. Using the simplest terms, crude they may be. We can’t watch a shrew change slowly into a monkey. Meaning the belief in macro-evolution is faith based. Meaning, yes macro-evolution is a religion.

Zach Miller said...

Well, Erik, I guess I have two answers to that. First, look at radioactive decay. While I can't recall off-hand what the half-life of carbon-12 is, I think it's in the thousands of years. You, me, or our kids will never see fully half of all the carbon decay in a carbon sample. But we know how quickly it decays on a daily basis. Using multiplication, it's pretty easy to get at the half-life. But it's not a matter of faith--the basis is there, and the oucome is inevitable.
Also, look at the fossil record. There are plenty of critters that can't fit into one category or the other. Archaeopteryx, for example, or Yinlong. Or Ambulocetus, Tiktalik, Australopithicus, Mahakala, Mesohippus...I could go on.
Again, the basis is there. Genetics works, and we see micro-changes (as you call them) in the lab all the time, as well as in nature. Why, in just 20 years, Darwin's finches recently changed their beak strength again. Another study showed that in just two generations, clams in the Pacific (I'm sketchy on the exact details) strengthened their shells after the introduction of a new shell-crushing crab.
It happens all the time. The basis is there, and the outcome is inevitable.

Zach Miller said...

And Yanconodon. I forgot that one.

Scott said...


"What I’m saying is the odds against a mutation that gives a substantial advantage are terrible."

I understand what you are saying. What you are saying, however, is wrong. Beneficial mutations are uncommon, but that does not mean that they are rare enough to qualify for terrible or even astronomical status.

What you perceive as random events--influenced only by chance--is, in fact, not all that random. Random elements do apply, but they are only a minor piece of the process of evolution.

Evolution is guided by natural selection (which you accept). All I've shown you is that the likelihood of a given beneficial mutation manifesting itself is not at all as unlikely as you've chosen to believe.

"Correct me if I’m wrong here but, dominant genes are slowly ousting the recessive genes right?"

No. Recessive genes will remain in the gene pool until they are eradicated from that pool by eliminating all the carriers. Pairing recessives with dominants only means that their likelihood of being passed on in offspring is not 100%.

The more frequently offspring are had with even one pairing of Rr, the more frequently Rr will manifest. And the next generation will see a further concentrated increase in Rr and rr combinations. If environmental conditions disfavor individuals with rr, they will be selected against, but this will not really affect carriers who don't express the gene (those with Rr).

"However it takes a leap of logic, some would say a leap of faith, to believe these small adaptations cause change from single celled organisms to extremely complex multi-cellular organisms."

It certainly does not. Changes in any given genome are going to be heritable, and will therefore be cumulative. Cumulative changes will add up to morphological changes over time (and sometimes not even very much time), and as the example inidcates, this gives rise to substantial morphologic differences.

Add in deep time (ie., generations upon generations), and the result is trillions of changes, cumulative because they are heritable, working within already viable populations, and guided by natural selection.

Since you accept microevolution, what you call macroevolution follows immediately thereafter, since, on a purely practical level, there is no difference between a small changes and large changes which are the result of many smaller steps (which is the essence of Zach's example).

"1. Macro-evolution has never been, nor ever will be observable."

Wrong. If you go here:

You can read for yourself a small portion of the substantial body of evidence for evolution observed.

Calling the modern synthesis a religion is only a consequence of your own ignorance on the topic. Rectifiable, if you choose to do so.

Scott said...

At Zach: the effective dating range for C14 to C12 is 58,000 to 62,000 years.

Erik said...

First. Radiocarbon dating. Yes you've heard it all before, but I'm saying it again. You can't possibly know the amount of C12 or C14 in the atmosphere at the time a dinosaur died. We simply don't know for sure, and cannot know, because we don't have 65+ million year old air. Sure, you can assume, but not without including your own personal bias.

"Plenty of critters that don't fit"
Are you saying your categories aren't perfect? A bold move, but not sure how it helps your arguement.....

The basis is there, for survival alone. Clams with thicker shells to not lead to clam reefs. You start with a clam, you end with a clam.

"Beneficial mutations are uncommon, but that does not mean that they are rare enough to qualify for terrible or even astronomical status."

Name one? Not meaning changes in beak strength, actual, beneficial, big advantage type of mutation? Give me an example here.

"Recessive genes will remain in the gene pool until they are eradicated from that pool by eliminating all the carriers"

Which seems to be entirely possible, given Rr and rr mating leaves only 50% chance of a "pure" genetic shortstack, the 25% chance of the purely dominant RR in any Rr Rr mating. And even 50% chance if RR and Rr get together. I don't even need to mention RR and RR. Seems like long odds to beat in generation after generation. Millions of generations later it's almost probable. At least, from the numbers.

Backward deformed finger on shrew-like being given time makes people... huh, I'll have to ponder that one. But isn't there some law.... 2nd (or 3rd, I forget now) of thermo-dynamics that states complex systems tend toward a maximum state of entropy over time? I've always seen the human body as monumentally complex.

Somehow going from less and less complex to more and more complex seems counter intuitive. Unless you're talking technological progress, which is niether natural or uncontrolled. Especially given the loss of genetic information in our RR example.

Such heated comments... !
"Calling the modern synthesis a religion is only a consequence of your own ignorance on the topic."

And personal attacks! It's almost as if I implied something about your religion! :D

Zach Miller said...

It's the law of entropy, Erik, and it says that in a closed system, processes become less complex (not more). While entropy can be summoned for any "system," it's basis is in engineering, and is often brought up as a point against perpetual motion machines. Now, that argument holds no water in terms of natural processes because Earth is an open system--it receives constant energy from the sun.

As for the genetic argument, look at CF again, and think about how many people are in the world. Even if less than 1% of the population has the CFTR recessive, they still must be getting together, because me and a lot of other people have CF. And it'll stay in the population forever. Recessive genes make the world go around. Also, it's not really fair to call recessive genes bad. There's that myth that dominant genes lead to beneficial mutations, but in reality both RR, Rr, and rr combinations result in different expressions of the same trait. My dad has rR of CFTR and shows no symptoms of CF. My mom has Rr and has asthma attacks (infrequently). I have rr and have CF.

And even among CF patients, a simple "rr" gene combo results in a WIDE variety of symptoms across the CF spectrum. I'm a "healthy" CF patient, but there are kids who are dying before their twelfth birthday because their CF is so severe. So even among one gene combo, there's still a lot of variation.

And one more point I'd like to make. There is no such thing as a "beneficial" or "harmful" mutation. It's all contextual, based on the environment. You'd think that CF is a harmful mutation, but if cholera were still a factor, it would certainly be beneficial. You'd think that a slightly slower, upright posture would be harmful, but given the new environmental context of ancestral hominids, it's actually beneficial.

Scott said...

First, Erik, I recommend learning the difference between a personal attack and statements made by someone who informs you that your ideas are wrong. I made no personal attacks. If I call your statements ignorant, there's nothing personal intended or implied in that. All I mean is that you are misinformed, and here is both a challenge and an opportunity for you to correct your situation.

Now then:

"You can't possibly know the amount of C12 or C14 in the atmosphere at the time a dinosaur died."

That's because C14 radiometric dating is not used to date anything older than 58,000 to 62,000 years, as I just said above. Non-avain dinosaurs went extinct 65 million years ago, so different isotopes are used to date strata from deep time.

It's obvious you should read more about radiometric dating, so here are some sites that should clear up your misconceptions: (this is a good resource, regardless of your religious persuasion)

"The basis is there, for survival alone. Clams with thicker shells to not lead to clam reefs. You start with a clam, you end with a clam."

And a bird is still a dinosaur. Yeah? And? Speciation does not ever imply that a new species leaves the group shared with its ancestor, so is your point that evolution has not occurred because you don't have any new nomenclature for the new species? Absurd.

"Which seems to be entirely possible, given Rr and rr mating leaves only 50% chance of a "pure" genetic shortstack, the 25% chance of the purely dominant RR in any Rr Rr mating. And even 50% chance if RR and Rr get together. I don't even need to mention RR and RR. Seems like long odds to beat in generation after generation. Millions of generations later it's almost probable. At least, from the numbers."

Long odds means no offspring. Period. The more generations you add, the more, not less, embedded in the population that gene will become. As soon as the 3rd generation rolls around, that gene will have propagated into the gene pool with the following potential:


r r
r rr rr
r rr rr

R r

r r
R Rr Rr
R Rr Rr

r r
R rR rR
r rr rr

R r
r Rr rr

This gives us a 32% incidence of RR, 36% of Rr, and 32% of rr within 3 generations. The only way to eliminate the gene is to destroy more than 2/3rds the entire population--and not just any 2/3rds, the right 2/3rds.

I don't know why you would persist on suggesting that the spread of genetic information is somehow unlikely. The numbers say the absolute opposite. 32-36-32 are not long odds, unless you are both bad at math and a terrible gambler.

"But isn't there some law.... 2nd (or 3rd, I forget now) of thermo-dynamics that states complex systems tend toward a maximum state of entropy over time? I've always seen the human body as monumentally complex."

Covered here:

"It's almost as if I implied something about your religion! :D"

Strictly speaking Erik, you know nothing about my religion, so it would be impossible for you to implying anything about it.

But since you seem to know little to nothing about either science or religion as systems of thought, here's some excellent commentary on both:

(Just plain good reading in general: )

Read 'em all. If you're still hungry for more yummy commentary, I have more. Feel free to contact me through my site.

Scott said...

"Name one? Not meaning changes in beak strength, actual, beneficial, big advantage type of mutation? Give me an example here."

Every attribute you have that is heiritable arose because of the feeback the environment had upon your ancestors, back countless generations.

But you need an example in order to grasp that small mutations can manifest themselves beneficially in the right environment?


Brian said...

Sorry I'm a bit late on this one, Zach. Overall you did gave a good general rundown of some important evolutionary ideas (i.e. convergence).

As Will and a few others have mentioned, though, the first part about human evolution needs some revision. I know you know that humans didn't evolve from chimpanzees, but the impression given by the post is that humans did evolve from chimpanzees. The direct human ancestors (prior to Australopithecus) are still elusive and proposed models are contentious. You seem to have based your idea for human evolution on the "savanna hypothesis" as well, being that early hominids were forced out of the forests and had to walk upright. Evidence from Laetoli, however, suggests that we were upright before the forests and woodlands receded, however, and the savanna model has largely been abandoned. I could send you some papers/references on these subjects if you like, although there is no shortage of hypotheses about human evolution these days and any model that is chosen is bound to be contentious.

Otherwise I think you did an admirable job here. When giving the lecture you should definitely play to your strengths (especially feathered dinosaurs), and homology/convergence is a very important idea to get across as well.

Oldfart said...

Ok guys. I found bauplan to be a word but boarders? Did you mean borders? Is boarders=borders in England or Canada or Australia? Not being an evolutionist, I have learned to be suspicious of any "misspellings" I encounter since your language is not always my language. :)

Millawub said...

At the risk of changing the argument, and proving my own ignorance of both the subjects in one blow, I wonder, can't God and evolution get along? (speaking of a christian based God here, just assuming thats what the anti-evolutionary posts are sided with)
Maybe I don't read my bible enough to see where it says evolution doesn't happen... any rate my understanding of creation based on having read genisis years ago was that over 7 days all life the universe and everything was created by God, order in which it happened may not comply with evolutionary beliefs.
Probably not supposed to represent 168hrs, maybe God took 168 billion years or whatever he felt like to get to what he called man in the garden of eden, through evolution even, so what. I kinda get the feeling when I read it, that much of the bible isn't meant to be taken literally. Maybe Adam and Eve represent the first group of what God was satisfied with as free willed beings intelligent enough to cure his boredom. Bible pretty much says thats why he created us. If thats so he did a mighty good job, I think we'd be pretty entertaining to watch as a whole.
If your a evolutionist (atheist variety), who or what started the spark of life probably doesn't matter to you since death will mean the end. If your a christian you probably shouldn't act in a way that will scare people away from christianity or just make them reject it because its the only thing that can save them from an eternity of hell.
Call me crazy, I believe in both.

Kate said...

So as a Biology teacher trying to understand all this, can someone PLEASE explain to me how natural selection leads to evolution. I get natural selection, but i don't get how the two populations become reproductively isolated from each other? (Because surely if one organism becomes reproductively isolated from the other population, its just as likely to be isolated from its own population?)I know we only have theories at this stage, but i'm keen to hear them!
Also - are there remenant populations or not?

Siderius said...

The split between micro and macro evolution is just something creationists have come up with when they no longer was able to just shrug off evolution, but still didnt want to swallow the whole thing.

There is no macro or micro evolution there is just evolution.

Its one process.

tiffany said...

hey, thanx for posting this. it has helped me with my debate at school. very helpful. thanx!

Jackie said...

Erik, I think you have micro- and macro- evolution wrong. Microevolution is basically just changes over small periods of time. Macroevolution are a changes over long periods of time. They Are not big changes over a small amount of time. Yeah changes could be either big or small but macroevolution itself just means over long periods of time.

Andrew said...

I know I am late to the party, but I was reading this post today. I just wanted to say, mainly to Erik, that micro-evolution and macro-evolution are not separate processes. They are simply the same thing looked at from different scales of time.

For example, if you agree that micro-evolution can occur, as we have tons of evidence for, you are at the same time saying macro evolution happens, because it is the same thing.

It's like saying, "I believe in millimetres but not kilometres."

Macro evolution is just looking at lots of micro-changes over a larger period of time.