Evolution 101

Sunday, July 30, 2006

Why Do Men Have Nipples?

Let’s start off with some listener questions.

From Elias: We humans are different since we have control over our environment not much change occurs, so survival of the fittest is no longer true. At the beginning of life was it just a big mess of a puzzle that fell into place over time? For example were there animals who had no reaction to predators hence they died off since they didn’t react to danger.

What I believe he’s trying to ask here is a question about the mechanism of natural selection. Does natural selection mean that you start off with a large group of random organisms, and then end up with only the few that are well-adapted to the environment? Well, sort of, but not exactly. This would make sense if one assumed that the environment was static- it never changed. But the environment is always changing, and so populations that are well-adapted today may be incredibly poorly adapted to it fifty years from now. A predator species that restricts the adaption of another species may go extinct, and allow the prey species to evolve into something different. Or predator species may be introduced to new species, which are not adapted at all to them. This was the situation with the dodo bird, which had adapted to easy island life by growing large and flightless. But when humans arrived, they were easy pickings for food from both humans and the other animals that were introduced by humans to their environment. Survival of the fittest still happens with humans, of course, and even though we do have incredible control over our environment compared to other species, we are not omnipotent.

From Richard: hey, just curious why you didn't mention the arguments against carbon dating in the podcast 122 - what is the evidence against evolution. I have heard this argument from many creationists.

I actually had a separate podcast on radiometric dating methods- the episode just prior to that, 121, titled “How Are Fossils Dated?” But yes, very often evolution deniers will criticize radiometric dating methods as a way of criticizing evolutionary theory. Usually, however, they don’t know what they’re talking about, and one easy way to tell is if they talk about “carbon dating” and “fossils” in the same breath. Radiocarbon dating is really not useful for most fossils, since it can’t be effectively used for artifacts older than about 60,000 years. What evolution deniers are trying to do with this kind of attack is, not to address evolutionary theory on its own merits, or even to question the principles of radiometric dating, but just to try to inject as much uncertainty into the evidence from radiometric dating as possible. Usually they try to make the claim that radiometric dates are made in such a wide range that they can’t possibly be used accurately, or that they have been used in the past to make blatant mistakes. I’ve run into the bulk of these claims made by Kent Hovind and a lot of them are just outright lies or misrepresentations of the actual dating methodology. He makes a claim that living snails were tested by radiocarbon dating and shown to be 2300 years old. What he doesn’t say is that a lot of the carbon in the snails’ shells was derived from dissolved limestone, which was very old, and screwed up the ratio of radioactive to nonradioactive carbon in the water.

From Lee: I just heard and enjoyed your interview on the biota.org podcast, and I thought that you and/or your audience might be interested in an OpEd that I published on evolutionary computation and intelligent design in the Boston Globe last year (August 29, 2005). It's a short, easy read and I've received a lot of feedback from non-scientists saying that the case that it makes is particularly compelling to them because it requires no familiarity with molecular biology, or with the fossil record, or with other areas of science. It is available directly from the Globe here. Alternatively, I have a local copy here.

Thanks, Lee, I had a great time on the Biota.org podcast, and I understand from Tom that it was very well received on his end as well. Digital evolution tools are already and will continue to be great tools both for discovery and education, so anyone who’s interested in that subject can go check out your op-ed.

From Mike: My question is about mammals. How did mammals evolve from Reptiles? Are there transitional fossils of egg laying / lactating species? Reptiles with nipples? I’m sure such a leap had to take thousands if generations. Have any such fossils ever been found to your knowledge?

The short answer is, mammals are distinguished from reptiles partially because of their ability to lactate. So, no, simply by definition, there are no reptiles with nipples, at least no extant species. By looking at the mammal clade as it exists today, it would seem to indicate that the whole nipple-mammary gland structure as it generally understood among mammals today wouldn’t have existed at all in reptiles, although it’s not known precisely when this trait evolved in mammal evolution. Let me just go through the basic steps of mammalian evolution quickly. Mammals and reptiles are both part of the larger clade, the amniotes. Of these, there is a further division into the reptilians, which would include turtles, lizards, snakes, and birds. Yes, that’s right- birds are cladistically reptiles, even though they used to be thought of as similar to mammals, since they’re warm blooded. But the bird singing on your fence is more closely related to the lizard sunning itself on a rock in your garden than to the cat watching both of them at your window. The other division in the amniote clade is the synapsids, which as a group is also very reptilian, but are different from all the other reptiles we know today. The characteristic that made these animals different is primarily the presence of an opening in their skulls just behind their eye. This may seem like a trivial distinction, but it allowed for stronger jaw muscles to develop, and much of an organism’s evolutionary fitness is tied directly to how well it’s able to eat. What makes this especially hard to conceptualize, is that of most of the synapsids, we would recognize nearly all of them as indistinguishable from reptiles, but we would be more closely related to them than we would be to a snapping turtle. However, among this group of synapsid reptiles, a subgroup evolved which we call the therapsids, and it is this group which eventually gave rise to modern mammals. The therapsids are often referred to as “mammal-like” reptiles. It’s within this group that warm-bloodedness evolved, the bones of the reptilian jaw moved into the mammalian ear, scales were lost, and fur eventually began to grow on some of the later therapsids. Eventually, an even further subgroup of the therapsids, the cynodonts, which were small, shrew-like organisms. Finally, from these small organisms, have evolved all living mammals, from whales to elephants to lions and tigers and bears, and humans. So yes, mammals did evolve from reptiles, and we can still see some hints of that in living mammals today- the monotremes. These include the duck-billed platypus and the echidna, both of which lay eggs instead of giving birth to live young, which the other two mammal groups, the marsupials and the eutherians, do today.

Interestingly, and to get back to the nipple question, monotremes do provide milk for their young, but they don’t have nipples. Instead, the milk is secreted sort of non-specifically from their skin, and their young lap it up off of their fur. So nipples as a physiological structure would seem to be a relatively recent evolutionary development in the history of mammals, and not even one that is necessary to be designated as a mammal.

But this brings me to another interesting nipple topic, and one that is commonly brought up in evolutionary discussions- why do men have nipples? It seems pretty obvious that for females, these structures are of obvious utility, both to mother and child. But wouldn’t it be just as useful for the child to have access to milk from both parents? In many species, food is provided for offspring by both male and female parents, to the obvious advantage of the young. This is a common behavior in birds, for example. Why, then, are male mammals so selfish? Why is there no such thing as the milk of male kindness?

As above, I’ll give a short answer and a long answer. The short answer is, men don’t nurse because we don’t have to. It’s not in our interest, evolutionarily speaking. The long answer is there is absolutely no physiological reason why men couldn’t nurse babies- all the equipment is there. The development of mammary glands in embryonic development happens independently of sex- for all intents and purposes, these glands remain indistinguishable between the sexes until puberty, during which exposure to hormones from the ovaries, adrenal glands, and pituitary gland. Pregnancy further enhances the development of these glands, especially the hormone prolactin. But exposure to the same kinds of hormones at the same times would give the same results for men, or, more specifically, removing the masculinizing hormones like testosterone. Mutations of the testosterone pathway can cause males to be born without recognizable masculine genitalia, and they develop usually into extremely beautiful “women”, with long legs and full breasts, simply because they’ve had their masculinization progress impaired. Genetically and genitally they’re still male- they have internal testes, not ovaries, but they sport breasts that could grace a magazine pictorial.

But, even without the full-on breast development that is caused by hormones, men can still lactate. Even human women who have never gone through pregnancy can induce lactation by mechanical manipulation of their nipples, since the nerve stimulation causes expression of the same hormones that induce lactation after pregnancy. These same hormones can be induced in males, making it the case that, if a man really wanted to breastfeed his child, all he’d really have to do is… well, practice.

So, we can see clearly that there’s no big physiological barrier standing between men and the ability to lactate. So what’s the reason why they don’t, especially because they do have nipples, after all? The reason is not physiological, but evolutionary. In the vast majority of mammalian species, offspring are born and raised solely by the female- the male plays no parental role at all. His evolutionary interests are best served by having children with as many females as possible, and so he doesn’t gain any advantage to sticking around to help raise one or two of them. According to the rules of evolutionary selection, whichever organisms pass on the most copies of their DNA are the most successful. I hesitate to use the word “rules,” because that makes it seem as if evolution was a game being played by all creatures, but that’s sort of how it works out.

But what about those species for whom males do play some role in the parenting of their offspring? This would include humans, of course. Well, we see that the male contributions in these species include things like bringing back food for the female, chasing off potential competitors within its species, and looking out for predators from other species. These alternatives to lactation are well-adapted traits for the species in which they’re found, and offset any benefit which male lactation would provide evolutionarily. But this doesn’t preclude the existence of any species for which male lactation would be an evolutionary benefit, and in fact one has been recently discovered, the Dyak fruit bat found in Malaysia. Males of this species were discovered with functioning mammary glands, both full and drained, indicating that they were providing milk to their young. This species hasn’t been studied enough to determine why male lactation was advantageous for development, but as you should know already, the physiological requirements would already have been in place. As bats are closely related to humans (just outside of the primates), this seems to suggest that male lactation in humans is only a few environmental variables away from becoming commonplace. Certainly it’s not outside of the range of personal choice, although cultural pressures may discourage this behavior.

So, to review, males have nipples because the development of mammary glands is independent of sexual development, at least until puberty. And the reason why men don’t use those nipples is because, at least so far, it hasn’t been evolutionarily advantageous for us to do so, although physiologically, we have essentially the same equipment as females and can produce a comparable product.

Sunday, July 23, 2006

What is Punctuated Equilibrium?

I received a message from a listener, DH, that I wanted to pass along to all of you. In the popular culture, oftentimes the idea is propagated that evolutionary theory is a controversial theory within science itself. This could not be further from the truth, and an international organization of science academies, the IAP, has released a statement that clarifies their official scientific position in regards to evolutionary theory. I’d like to read that statement to you now:

We, the undersigned Academies of Sciences, have learned that in various parts of the world, within science courses taught in certain public systems of education, scientific evidence, data, and testable theories about the origins and evolution of life on Earth are being concealed, denied, or confused with theories not testable by science. We urge decision makers, teachers, and parents to educate all children about the methods and discoveries of science and to foster an understanding of the science of nature. Knowledge of the natural world in which they live empowers people to meet human needs and protect the planet. We agree that the following evidence-based facts about the origins and evolution of the Earth and of life on this planet have been established by numerous observations and independently derived experimental results from a multitude of scientific disciplines. Even if there are still many open questions about the precise details of evolutionary change, scientific evidence has never contradicted these results:

1. In a universe that has evolved towards its present configuration for some 11 to 15 billion years, our Earth formed approximately 4.5 billion years ago.

2. Since its formation, the Earth – its geology and its environments – has changed under the effect of numerous physical and chemical forces and continues to do so.

3. Life appeared on Earth at least 2.5 billion years ago. The evolution, soon after, of photosynthetic organisms enabled, from at least 2 billion years ago, the slow transformation of the atmosphere to one containing substantial quantities of oxygen. In addition to the release of the oxygen that we breathe, the process of photosynthesis is the ultimate source of fixed energy and food upon which human life on the planet depends.

4. Since its first appearance on Earth, life has taken many forms, all of which continue to evolve, in ways which palaeontology and the modern biological and biochemical sciences are describing and independently confirming with increasing precision. Commonalities in the structure of the genetic code of all organisms living today, including humans, clearly indicate their common primordial origin.

We also subscribe to the following statement regarding the nature of science in relation to the teaching of evolution and, more generally, of any field of scientific knowledge: Scientific knowledge derives from a mode of inquiry into the nature of the universe that has been successful and of great consequence. Science focuses on (i) observing the natural world and (ii) formulating testable and refutable hypotheses to derive deeper explanations for observable phenomena. When evidence is sufficiently compelling, scientific theories are developed that account for and explain that evidence, and predict the likely structure or process of still unobserved phenomena. Human understanding of value and purpose are outside of natural science’s scope. However, a number of components – scientific, social, philosophical, religious, cultural and political contribute to it. These different fields owe each other mutual consideration, while being fully aware of their own areas of action and their limitations. While acknowledging current limitations, science is open-ended, and subject to correction and expansion as new theoretical and empirical understanding emerges.

Signed to this statement are the national academies of sciences from 66 countries, including the United States, the United Kingdom, Poland, Ireland, Italy, Greece, Hungary, Japan, Lithuania, Germany, Austria, Australia, and interestingly enough, Iran. It’s great to see such clear international support for science, and I think that everyone will eventually take notice of it.

On a similar note, I received a question from JM asking me about the beliefs of the current Pope about evolutionary theory. Pope John Paul II, as some of you are probably aware, was fairly well-educated about science, and accepted evolution explicitly in a 1996 speech, although he warned against the acceptance of any material explanation for the existence of the human soul. The current Pope Benedict XVI, before he was elected, made statements accepting of evolutionary theory as well. Recently, the Vatican’s chief astronomer explicitly endorsed evolutionary theory and rejected intelligent design as unscientific. However, other statements made by Catholic officials support the idea that the evolutionary process is guided by the divine, although the specific details of this are never made clear. This seems to be essentially the position that’s promoted by Dr. Kenneth Miller, the author of “Finding Darwin’s God.” In that book, as I’ve mentioned before, Dr. Miller explains evolutionary theory in very basic language, dismisses the claims of intelligent design proponents, and provides room for his faith. I would recommend that book to anyone interested in evolution just in a general sense, but especially to those who consider their faith as an obstacle to the acceptance of evolutionary theory.

Today I’d like to talk about punctuated equilibrium. This concept was coined by the famous paleontologist Stephen Jay Gould, and it has become somewhat of a controversy within evolutionary theory. This fact is, predictably, seized upon by various evolution deniers as a way to challenge evolutionary theory as a scientific theory, as if to say, “Aha! The scientists disagree about evolution! Therefore, it is wrong.” But this is unfounded. Scientists disagree all the time- by that logic, all scientific theories are null and void, because there’s always some controversy going on at some point in time about some aspect of just about every theory.

What is meant by the term, “punctuated equilibrium” is that, throughout evolutionary history, the evolution of one species to another has not been a constant process, but has instead been one of population stability followed by rapid speciation, followed by long periods of stability. You might be wondering, “Why is this controversial?” but in the definitive paper on punctuated equilibrium, published by Gould and Niles Eldredge in 1972, they made the case for their concept as an alternative to what they called, “phyletic gradualism.” This would be the opposite to what they proposed of the stability-speciation-stability model of evolution, and would describe the situation of whole populations speciating slowly, and constantly over time.

To give you a better idea of the distinction between the two, just imagine a child growing. When it is born to just prior to puberty, the average child grows pretty gradually and steadily. This is roughly the kind of change that is thought of with phyletic gradualism. Now imagine that same child going through puberty, and experiencing growth spurts. It could go one or two years without growing much at all, and then over a three month period shoot up several inches. Then maintain that height for another year, and then experience another growth spurt. This is roughly the kind of change that is thought of with punctuated equilibrium. There are long periods of little to no change, or equilibrium, which are punctuated by short periods of rapid change.

This does not imply in any way that new species spring into existence instantly and magically. Just like a growing child doesn’t snap its fingers and shoot up three inches, new species don’t just “appear” out of nowhere. This is called “saltation,” and it’s associated with ideas like creationism, not evolutionary theory.

So, why did Gould and Eldredge even come up with this concept anyway? Were they just sitting around, trying to come up with ways to pick fights with other scientists?

The reason for the theory comes from the natural evidence, actually the fossil evidence. Throughout the course of paleontological investigation, fossils of any given species were found, more or less with the same basic anatomy, throughout the range of their presence in the fossil record. As one moved along the geological column closer to present day, one would find descendent species that were obviously related by their anatomy, but were different enough to be classified as different species. And so on and so forth, with daughter species continuing to be found in more recent strata, but again, with very little gradation among the species population. If you recall from the podcast on transitional species, this same phenomenon is latched onto by evolution deniers as being “gaps” in the fossil record, and is seen as a refutation of evolutionary theory.

The common objection is that, if evolution is true as Darwin described it, then we should be able to dig into the ground, find the fossil of a species, dig a little farther, find the fossil of its parent that looks slightly different, dig again and find its grandparents that look even more different, and dig once again to find its great-grandparents that look different enough to be classified as a different species altogether. That’s somewhat of a simplified account of that objection, but it encompasses the intended spirit. Essentially, deniers of evolution claim that we should have an unbroken chain of fossils that demonstrate the minute evolutionary changes over time. That is, we should not only have fossils that demonstrate separate species, but we should also have the fossils of the organisms that are in between those species.

If you remember from the podcast about the concept of a species, you’ll of course realize how silly a request that is. Fossil species are defined retroactively- there isn’t some kind of label that switches from one species name to another as populations change.

In addition, consider that the geological record is not perfect. It’s not a filing cabinet where fossils are neatly ordered, ready for discovery by paleotologists. It is incredibly unlikely that the remains of an organism will become fossilized instead of decomposed, and even for those that become fossilized, their continued preservation is not certain. Fossils are destroyed all the time, by seismic activity, volcanic activity, and erosion.

However, even given that consideration, what punctuated equilibrium does is explain the pattern of the fossil record in a way that is consistent with evolutionary theory. Namely, that speciation involves a small group of organisms with the parental population, this group is typically isolated geographically from the parental population, and this genetic isolation promotes rapid morphological change in the daughter species population. Because of this, fossil records of the parent and daughter populations will appear to be geographically and chronologically distinct in the geological column. This concept really isn’t anything that revolutionary when you think about it- the famous evolutionary biologist Ernst Mayr had conceived of both of those mechanisms long before Gould and Eldredge came around. In trying to figure out mechanistically how species develop, he came up with peripatric speciation, in which a small subset of a population forms into a new species population, and allopatric speciation, in which geographically isolated members of a population form a new species population. If that sounds exactly like what happens in punctuated equilibrium, you’re basically right- and this is what the real controversy is about.

Within the scientific community, it’s never been a question of whether evolution was right or wrong, or whether punctuated equilibrium was right or wrong. For the most part, punctuated equilibrium was accepted by the scientific community almost immediately. What is in dispute, rather, is to what extent punctuated equilibrium was in agreement with Darwin, and to what extent it differed from evolutionary theory prior to the Gould and Eldredge’s introduction of the concept. It’s true that Darwin wrote extensively about the concept of gradualism in his work, but he seems to have anticipated an idea like punctuated equilibrium, as he suggested that the period of time in which a species doesn’t change is likely much longer than the period of time in which it does. You’ll remember that previously I mentioned that Gould and Eldredge had introduced the concept of phyletic gradualism as a counter to their own concept. Many scientists see this as a strawman, in that they made the case that Darwinism implied phyletic gradualism, to which they were proposing their own scientific alternative. This is simply not true of Darwin himself, and I’ve already mentioned that he anticipated the concept of punctuated equilibrium himself. Why Gould and Eldredge would have painted Darwin with such an inaccurate brush is a question I can’t answer, although it should be noted that Gould was known for speaking about his discoveries in a manner which some would consider overemphasizing their revolutionary nature, to the extent to which many people thought he was criticizing the existing tenets of evolutionary theory.

Essentially, punctuated equilibrium is an accepted part of evolutionary theory, and not only that, it’s a clear concept that follows clearly from the original theory as first conceived of by Charles Darwin all the way to present-day. It’s a very useful concept for understanding the patterns within the fossil record, and the only controversy that still exists is in regards to how revolutionary of an idea it actually was within evolution.

Sunday, July 16, 2006


I was interviewed this week for the Biota.org podcast, which focuses on the development of artificial life models. This field is of interest to evolution, because these models can be wonderful experimental tools to test out specific components of evolutionary theory without having to wait for hundreds of thousands of years, and they can also be great educational tools. One fun artificial life program that I’d recommend for you to check out is called, “Gene Pool,” and it can be found at www.ventrella.com. At any rate, check out the Biota.org podcast if you’d like to hear that interview.

This podcast is growing in popularity, and I’m getting more and more questions emailed to me. This is great, and I would encourage anyone who has a question to send it in, and I might even answer it on this podcast! This week, I’m not going to have a specific topic, and instead I’m going to respond to as many emailed questions as I can.

The first question is from Mark, although I received several similar emails from other people asking about a comment I made in response to an email that I answered last week. He writes:

You mentioned in the podcast that, although you are an atheist, you spend your Sundays in church. That was a little surprising, though not a lot. I continued to attend church for a few years after rejecting religion, I suppose out of habbit and for socialization. I was just curious as to why you continue to do so and whether you find yourself in situations where your scientific knowledge is in direct conflict with church lessons or issues.

Well, I’m sure that the idea of an atheist attending church seems a little strange to some people, but it’s a unique situation. I visit with a specific group at the church that examines issues that most people regard as being in opposition to religion, such as evolution. I go there every week, partially because I like interacting with the people there, and also so that I can provide accurate information about things like evolution that people there wouldn’t be aware of. You might think of it like an Evolution 101 house call, or church call, more accurately.

The next question is from Eddy, who writes:

macro and micro evolution When using terms like these it is hard to say that there is no difference between the two.... Dr. Raoul A. Robinson defines a difference between macro and micro evolution. Two distinctions he makes are: - timescale, some changes can occur in relatively short period of time (decades to millenia) - persistence, some change occur, but can be changed back... Does this makes sense?

Well, Eddy, I touched on micro and macro evolution back in podcast 102, where I looked at examples of what evolution is not. Dr. Robinson is correct in that, typically we think of microevolution occurring over a short period of time. However, the best distinction that could be made is that microevolution is that which does not change one species into another, and macroevolution is that which changes one species into another. But the only difference here is timescale, not mechanism. The same mechanism that causes an organism to gain a single trait is the same mechanism that causes a new population to speciate from another. We’re only talking in difference of scale. As a comparison, think of a garden hose- turn the water on high, point it at the ground, and within a few minutes you’ve cleared out a good-sized rut in the dirt. Nothing too special- that’s the force of erosion at work. But instead of running it for ten minutes, what if you run it for ten years. How big a rut do you think it would be then? What about ten thousand years? Now you’re getting a sense of the difference in timescale between micro and macroevolution. Or you can think about economics. Do you think that the five dollars you spend at Wendy’s to buy a chicken sandwich affects the amount of money the store makes in a day? Of course it does. What about the millions of customers ordering chicken sandwiches around the world- does that affect the multimillion dollar deal they make with an advertising company? Of course it does- same mechanism (people buying chicken sandwiches), just an increase in scale. Remember that the next time anyone tries to use micro and macroevolution as a way to deny evolutionary theory.

The next question is from James. He writes:

All my life (almost 54 years now), I have heard statements regarding the evolution (in humans) of a larger brain being significant; that evolving a larger brain is what made us more intelligent (whatever that is) than other animals. So, my thoughts are: Elephants have larger brains than humans. Why aren't they more intelligent than us? I believe some whales also have brains larger than humans. The average man has a bigger head than the average woman, but women and men seem to be equal in intelligence; some people have tiny heads, but are very smart, while others have large heads, and are quite stupid. My hypothesis is that brain size is insignificant (beyond a certain point). It must be how the brain is organized that really matters. Brain structure, along with proper wiring or programming (a.k.a. experience), is what makes the difference, not the size. Am I right? And if I am, why do scientists and teachers (including yourself) constantly refer to brain size instead of brain structure? I hope the question is not stupid. If it is, perhaps my brain is too small.

Well James, you’re right- brain structure is important, but so it brain size. But it’s not just brain size as a single measurement- what seems to be most important is the ratio of brain size to body size. That is, the higher the ratio, the more brain per body weight, and the more intelligent the animal. This is called the Encephilization Quotient, or EQ. Primates have some of the highest EQs of all mammals, with humans obviously at the top of that list. Dolphins also have a very high EQ, which shouldn’t be any big surprise, since they’re widely known to be relatively intelligent also. Interestingly, octopi have the highest EQ of any invertebrate animal, which means they may be spineless, but they’re pretty smart. But EQ isn’t a perfect measurement- because of their small size, shrews have the highest EQ, and they don’t seem to be particularly intelligent. So absolute brain size is also important. Curiously, Homo neandethalensis, or Neanderthal Man, had a larger brain than modern humans, but there is no indication that they were particularly intelligent, or at least more intelligent than the human ancestors that lived at that time. This may have been because they lacked language, since their throat structure wasn’t likely condusive to the development of language. The development of structures within the brain, specifically the neocortex, is what sets humans apart from other organisms. This region of the brain is where the intellectual and reasoning capacity exists, and differences in this region are likely more important among humans for determining intelligence than absolute brain size.

The next question is from DR, who writes:

In your last podcast, #123, you gave examples of homosexuality in other animals. But all the examples seem to show 'homosexual behavior' but overall the animal was bisexual. Are there any examples that we know of where the animal is purely homosexual. For example, I have friends who are homosexual who do not mate with women--they are not attracted to women at all--there is no sometimes. That is homosexuality. In the examples you gave all the animals were bisexual. So are there any animals that are homosexual (besides human animals of course) ?

This is true- the examples that I gave were of various species pursuing homosexual interactions part of the time, while also pursuing heterosexual interactions for the other part. The purpose for doing so was to show that homosexual behavior is not fatal to evolutionary theory, and in fact can provide reproductive fitness to the population. But there are many examples of individuals in populations seeking out exclusively homosexual interactions- I’m sure many of you have heard of the “gay penguins” that refuse the attraction of females, and studies have seen that some male bighorn sheep actually prefer males to females. It’s just as tricky defining this as strictly homosexual in terms of orientation, because we can’t actually ask the animals which they prefer, and even in humans, many heterosexuals engage in some homosexual interactions at some point, and many homosexuals engage in some heterosexual interactions at some point as well. So, remember that I said sex isn’t black or white? This is why.

The next email is from Eddie, who writes:

I debate often with creationists in an internet chat room and the issue of random vs. nonrandom comes up often. I enjoyed your podcast on the subject but had one comment. At the end of the podcast, after making a great case that causality/environment is essentially the determining factor in mutation and which mutations survive, you end by saying evolution is both a random *and* a nonrandom process. This i thought re-opened the door on the very debate you were trying to close. As true randomness is theoretically impossible (it would be an effect with no precedent) in a causal system. No computer model of true randomness has ever been created. And there is nothing at all random about evolution. However the extreme complexity of the systems are so far beyond what we can calculate that it just appears random to us.

You’re right- in a deterministic universe, nothing is truly random, but from our perspective, mutations are generally unpredictable events, or at least the specific mutations are unpredictable- we know pretty well that if you expose DNA to UV radiation, you’ll get thymine dimerization, but we can’t predict which bases will and which will not dimerize. We know that mutation rates can change, and that some regions of a genome are more likely to mutate than others, but it’s still a generally unpredictable process. What’s more causally apparent to us are the environmental factors which affect reproduction fitness and mortality- these are obviously nonrandom. So that’s really what I mean by evolution being both nonrandom and random- I hope that clarifies my position.

This next email is from D.B.

Why is it that humans can hear there own thoughts in our heads with out speaking the words that come out of the mouth?

We can hear our own thoughts because all our senses are processed in our brain. So, we don’t technically need our ears to “listen” to something, just as we don’t need our eyes to “see” something. What is an interesting question to consider is whether or not other animals have that same ability. No other creature has such an audible language as humans, but do they represent their thoughts symbolically in their minds as they’re thinking them? It’s something fun to ponder.

Jeff asks:

I was listening to a creationist poodcast the other day when one of the speakers said that Stephen Hawking is a deist.

Supposedly Stephen Hawking said that the universe is so extremely complex, and the probability of the universe and life coming into existence is so small that there must have been an intelligent creator who created the universe.

I would like to know how you would respond to Stephen Hawking's statement from an atheistic point of view.

That quote sounds bogus to me, especially since Hawking just gave an interview in China recently where he said, “There is no evidence for intelligent design. The laws of physics and chemistry, and Darwinian evolution, are sufficient to account for everything in the universe.” But, if you want me to respond to that statement in general, regardless of who actually said it, I would say that it sounds like a combination of an argument from incredulity, and also a misunderstanding of statistics. For example, it is incredibly improbable that I will win the lottery today. But it is incredibly probable that somebody will win the lottery today. Thus, it may have been improbable for life to arise in one specific place, but very probable that it did arise somewhere.

And finally, one last email from John:

Recently, an anti-evolution friend of mine, whose studying computational biology, asserts the following to me contra Darwin:

"the fact that no random polypeptide chain ever folds into a stable native state at all, let alone into a nontoxic one, let alone into a specifically useful one, let alone into a specifically useful one which is preserved through natural selection."

Not being a biochemist or biologist, I couldn't immediately respond. Is this true to your knowledge?

This is a similar problem to the statistical improbability I mentioned in the previous email. It’s true that any given random polypeptide chain won’t fold into a stable conformation, but would likely just flop around with one or two interactions between different residues in the chain. Most proteins are combinations of two different types of conformation structures- a helix, like a DNA spiral, or a back-and-forth folded sheet. What this problem ignores is the fact of selection- if you have a large number of different proteins, most of them will be useless, but one will be useful. It’s just like with the lottery example- it’s improbable that any one person will win, but it’s certain that somebody will win. Just like this, although any random protein won’t fold into a useful structure, the genome doesn’t encode for random proteins, and neither does evolution conserve random proteins. Small random changes are made to individual proteins, and those changes are selected for their relative effect on reproductive fitness, after which the changes are increased or decreased in a population. That’s evolution in a nutshell. You might say, evolution 101. That’s all for this week, take care.

Sunday, July 09, 2006

Why Did Homosexuality Evolve?

All right, now to start things off with some listener email. I’m very pleased to have received my first critical email. You might think that podcasting on a topic that is so controversial in the popular culture would get me lots of criticism, but I’ve only received positive comments so far. That is, unless you check out the reviews on the iTunes page- there have been a number of 1-star reviews. But this email, although it’s critical, is so polite I just have to share it with you right off the bat.
Dear Dr. Zach,

I hope you are well and your weekend is running smoothly.

The Infidel Guy recently turned me onto your podcast, apparently he holds you in high esteem.

I was excited to hear the gospel of evolution from an educated person, as most of the times I hear it spouted are from high-schoolers and fellow workers, who are innocent in the fact that they believe in evolution simply because it has been crammed down their throats.

I expected your podcast to at least acknowledge the number of evolutionary frauds that have been presented(all of them) and the number of evolutionary evidences that stand before science(none of them).

I was dissapointed to hear your podcast sounds like someone reading a public school text-book. I was hoping to at least hear about microbial evolution or evidences that may be true that I haven't heard of, instead I hear things like, "We Suppose" "The evidence suggests" "The Fossil Record" and I wonder exactly which evidences have solidified your understanding of evolution, because it is all clearly a religion, and the most boring fairy tale ever told, to those of us who understand the theory.

The main evidence that it seems you are relying on for the foundation of your religion is the occurence of variation within a species. The correct term is variation, evolutionists such as yourself have misnomered it to be "Micro-Evolution" so you can piggy back upon something that has actually happened. Micro-evolution(I'll use your word) will NEVER lead to a new improvement of a species or the formation of a new species.

I hope you have a good Sunday, please consider spending it in Church.


Well, C.S., as it happens I do spend my Sundays in church. Although, I can’t see what that has to do with evolutionary theory. I’m glad to hear that you connected to this podcast through the Infidel Guy- as my long-time listeners know, he was the one who first conceived of Evolution 101. I certainly haven’t had evolution “crammed down my throat” as you say, I’ve been learning as much as I can on my own, since it is so scientifically compelling. Hopefully, I can communicate enough of what I know to creationists who have had nothing but pseudoscience crammed down their throats, instead of real science. I’m not sure which evolution “frauds” that you’re talking about- although I can hazard a guess. Nebraska Man? Piltdown Man? The thing is, these just aren’t scientifically relevant anymore- who do you think recognized them as frauds? Scientists! The only people who are interested in them anymore are creationists, because they think that bringing them up can poke holes in evolutionary theory now. That’s just not the case- if you’ll check out my podcast on human evolution, you’ll see that they’re not even part of the equation. Also, I’m not quite sure why you think I haven’t presented any evidence for evolution. I did a whole series on the molecular evidence for evolution which I’m quite proud of. Evolution is decidedly not a religion- it makes no claims about a deity, its advocates don’t get together once a week to sing songs about how wonderful evolution is, and I don’t pray to Charles Darwin. Regarding “micro-evolution,” actually it is creationists who use this term much more often than those who accept science. I’ve already discussed the reason why there isn’t a difference mechanistically between micro-and macro-evolution, any more than the difference between micro- and macro-economics.

All right, well, thanks from C.S., and now for a more inquisitive question:
The environmental pressures that lead to the reproductive selection of certain changes or mutations seem to be at a very gross level, such as at the level of reproductive success or survival.

How, then, does evolution effect something like eye color, skin color, size, cholesterol production in the liver, the presence or absence of a pinky toe, intellect, etc. that don't seem to directly effect reproductive success or survival? How does/did our body/species select for subtle changes that are effectively invisible to natural selection?

From H.G.

The reproductive success of a population isn't just one trait- instead, fitness is a comprehensive quality that takes into account lots and lots of traits. Any individual trait that gives any reproductive advantage, no matter how small, will be increased in a population over many generations.

For any given trait, we can arrive at conclusions based on what we presently know about the relative fitness associated with the presence or absence of that trait. For example, eye color (essentially the presence or absence of pigment in the iris) has historically been segregated geographically. The lack of pigment (blue eyes) occurs with the greatest frequency in Northern European populations. We know that this region tends to experience less direct sunlight, especially at the higher latitudes. We also know that other organisms that are exposed to very little light also lose pigment over time. This is either because the selective pressure to keep pigment drops (it does cost energy to make pigment molecules, after all) or because there is a selective advantage to have little pigment. Skin color is likely due to the latter- Northern Europeans also lack much pigment in their skin. There may be an advantage to their ability to synthesize Vitamin D in these environments, but I'm not sure if this has been established empirically.

There are some traits that are obviously of no bearing to reproductive success whatsoever. For example, the ability to roll your tongue. I can do it, others can't, and unless it's linked to some other important trait, it seems to be just a weird genetic coincidence. It might be left over from some earlier period in human evolution, perhaps from our smaller, fruit-eating primate ancestors. For now, though, it's a trait that just randomly shuffles through the generations, until some change in our environment makes it imperative for reproductive success.

All right- well that’s enough questions for this week, on to the main topic: why did homosexuality evolve? I realize that, just as with evolution, homosexuality is still somewhat of a controversial issue in pop culture (well, at least in American culture, for my international listeners). But nothing’s more interesting then sex, and what could be better than sex and evolution?

The common argument goes like this: if evolution is true, then only those individuals who are able to reproduce will contribute offspring to the next generation. Thus, individuals who are homosexuals will not be able to reproduce, their genes will not be passed on to the next generation, and so if there is some genetic or biological reason for homosexuality, evolution should have removed it a long time ago.

First of all, is homosexuality a specifically human behavior? If it is a fundamentally biological behavior, there should be some other species which share it. And, in fact, there are close to 500 known species which are known to engage in homosexual behavior, including elephants, dolphins, sheep, bears, deer, rats, cats, dogs, cows, rabbits, kangaroos, squirrels, whales, bats, pigs, mice, goats, as well as just about every other primate. And that’s just the mammals! There are many more birds, fish, reptiles, and even insects which have also engaged in homosexual behavior.

So it really doesn’t seem as if homosexuality is really all that uncommon. But so what? Why should homosexuality be a trait found in so many organisms if it’s so fatal to the evolution of the species.

Well, the answer is, as with most things I discuss here, that sex really isn’t black and white. And homosexuality isn’t fatal to the evolution of species. Remember the definition I gave for evolution way back in the first podcast- “change in allele frequency in a given population over time.” There’s a reason why I specified “population,” and not “individual.” Individual organisms don’t “evolve” any more than a single pixel makes up a picture on your computer screen. What is necessary for evolution to take place is for there to be a group of individuals, a population, within which genes can change and flow.

Now, it certainly is the case that, for most organisms which utilize sex, heterosexual sex is required for propagation. But consider- not all species employ strictly monogamous sexual strategies. For many species, males compete for control of several females, meaning that there are many males who are left out in the cold, so to speak, with nothing but each other and raging libidos. One hypothesis fits this scenario- homosexuality occurs in these organisms to placate the male aggression that is left over after competition for females.

But that doesn’t mean that homosexuality is always a consolation prize. Among the American Bison, male-male intercourse accounts for almost half of all mating, and not just among the losers. Both parties seem to enjoy themselves, with the subordinate male even accommodating the advances of the dominant male. The same phenomenon can be seen in bighorn sheep, where the male being mounted even adopts the arched-back posture called “lordosis,” which is typically associated with the female sexual response. Clearly, these animals seem to be enjoying what they’re doing.

But the males don’t get to have all the fun. Female homosexuality is also common, with female antelope mounting each other in simulation of heterosexual courtship behavior when males are not present. In bonobo chimpanzees, the female-dominated social network is composed of close bonds which are shown by frequent homosexual interactions between female members of the group. In fact, more than half of an adult female bonobo’s sexual interactions will be homosexual in nature.

So how, you’re probably wondering, do these populations ever manage to reproduce with so much homosexuality? Well, the reason is because, as I said before, it’s not that black and white. Sure, individuals engage in homosexuality some of the time, or even a lot of the time, depending on the species. But not all of the time- they still find time to mate heterosexually. Sex seems to be a very fluid trait in many animals- pretty much any sexual configuration that can be performed within anatomical limits is done by some kind of animal. Sorry to say, but although humans can be kinky, we’re just not that original.

Now, you remember that I said that evolution takes place in populations, not individuals? Well, consider the social benefits of a population in which all members can share the close bonds of a sexual relationship, not just males and females. Clearly, in the case of bonobo chimpanzees, the bonds formed between females by homosexual relations are socially stabilizing. A stable society is much more likely to promote successful reproduction of young. Thus, homosexuality would be an evolutionarily beneficial behavior.

But what about some molecular evidence? Well, if you’re hoping that a “gay gene” has been found you’re not in luck. One hasn’t been found, although more and more scientists are starting to look at the genetics of homosexuality. Most likely, homosexuality as a behavior is a more complex phenomenon than just blue or brown eyes- a number of factors are considered- including the number of older male siblings a person has. Scientific research out of Toronto has shown that the more older male siblings a man has, the more likely he is to be a homosexual. The hypothesis is that the mothers becomes immunologically sensitized to the successive male fetuses within her, since they contain male proteins that she is not used to. According to this hypothesis, by the time the youngest male child is being carried in utero, she has developed anti-male antibodies which effectively diminish the normal masculinization process, resulting in a tendency towards homosexuality. But there may be some other benefits to the mother- a recent study from Italy showed that the maternal relatives of homosexual men have more children than the maternal relatives of heterosexual men. If this is repeated, it would suggest that there is a reproductive benefit to women whose DNA tends to result in homosexual male children- they have more children overall, meaning that their evolutionary fitness is actually increased because of the fact that they have homosexual sons. This is a fascinating possibility, especially because a better understanding of the genes involved in this phenomenon could have a major influence on our understanding of reproduction in general, and could point towards some better therapeutic targets for women who have problems with fertility.

All right- well, that was a lot to chew on for this week. To review- homosexuality is not a strictly human trait- it is practiced commonly throughout the animal kingdom. It has a clear evolutionary benefit in that it fosters better socialization among members of both genders. In humans, the evidence strongly suggests some kind of genetic component in the development of homosexuality, although the specific genes have not yet been discovered.

Before I sign off, I do want to make it crystal clear that the discussion here is in no way establishing a moral position in favor of, or against homosexuality. To do either would be to commit a clear naturalistic fallacy- to say that because something is natural, it is either right or wrong is clearly illogical. The moral discussion of homosexuality is reserved for other, non-scientific settings. Thanks for listening, and have a great week. I’ll see you next time.

Sunday, July 02, 2006

What is the Evidence Against Evolution?

I’d like to welcome any new listeners this week. The listenership here is growing steadily, and I have to say I’m very happy that so many have such interest in evolutionary theory. I’m certainly glad to have you all on board, and I welcome any questions you may have- remember, your questions are what drive this podcast.

Speaking of which, here’s the listener e-mail for this week, from Cameron, who asks: “We know that monkey babies are soon thrown on the mothers back after birth and have to hang on, and have that ability in them at birth. If a monkey was slowly evolving to human and evolution was taking place the offspring would not likely survive considering survival of the fittest and all. While the human eventually would become superior intellectually, they at birth they are quite helpless. If it was a survival of the fittest situation the more human a monkey became the less likely they would be to survive. If I was forming a theory to find the common cause I would say that monkeys would more likely have evolved from humans based on what is known on the care of babies. The humans would care for the child the same and eventually they would evolve to the point that they did not need all the care. Can you follow the logic on this? But of course we have to deal with the fossil record and that seems to say a different story. What do you think?“

Well, Cameron, I think I follow what you’re saying. You're saying that although you accept the evolution of the species, you're having trouble accepting that natural selection can account for it all?

Well, you're right- it's not as simple as "survival of the fittest." Ultimately, of course, what it comes down to is which members of a population are able to reproduce the most efficiently- but that doesn't always mean that the strongest or fastest is the one that fits the bill.

Sexual selection, for example, is a component of natural selection that very often runs counter to what we would anticipate in terms of the selection of certain traits. Take the peacock, for example. The male of that species sports a tail that is nonfunctional (although attractive), and costs him much in terms of energy to produce. Yet we also observe that females are most attracted to males which have the largest and most impressive tails- hence the selection. I should probably do a podcast on this subject soon.

Also, remember that the "selection" component of natural selection is a composite of all the environmental factors that affect any group of organisms- or lack thereof. For example, you mention the fact that monkeys cling to their mothers, and yet humans do not. What we also know is that humans differ in a number of significant ways from monkeys, including the amount of body hair. There are a number of hypotheses to explain why humans lost body hair (neoteny is one, which I feel is pretty strong), but consider that without body hair, it was impossible for babies to grab onto their mothers. Thus, natural selection kicks in. Any mother which treated her child like a monkey would have lost it, and would not have passed on any genes. Only those mothers who slowed down to carry their babies were successful in raising them to adulthood, and thus the genes which encouraged this behavior were passed on. Or it could have been the other way around- mothers stopped carrying babies on their bodies, and thus there was no selective pressure to keep full body hair.

Whatever the reason, the molecular evidence clearly shows that humans and primates are descended from a common ancestor. Common heredity is the ONLY phenomenon that has been observed which can explain two different organisms having the same genetic information.

All right, on to this week’s topic. The intended audience of this podcast is, as I’ve made clear many times before, those with no formal scientific training- laypeople, if you will. One of the confusing things about being a layperson in regards to some esoteric topic, is that there are always “experts” on both sides of the issue that are trotted out to voice the opinions of both sides, and it’s very hard to decide which experts are the most believable. Believe me, this is true for me in a lot of subjects- I may know my way around evolution pretty well, but there are a lot of things in science of which I find myself at a complete loss.

For those people that are inexperienced with the evidence for evolutionary theory, the arguments from those promoting the position of creationism can be just as confusing, especially when the creationist scientists are trotted out to make their arguments against evolution. So- who do you listen to? Ken Miller advocates for evolutionary theory, and Michael Behe advocates for intelligent design. Both men have Ph.Ds, both men are college professors, both men have published primary scientific literature, and both men have written popular books on the topic. Both men were even called to testify at the Kitzmiller v Dover trial. So… who’s right? And, more importantly, what can we look at to see?

Well, I’ve already done a podcast on Behe’s argument for Irredicble Complexity. Essentially, he argues that certain biological systems are so complex that they could not have evolved from simpler systems, and thus he posits the existence of an intelligent designer to explain their existence. I already explained why, logically, this is fallacious, because it is an appeal to ignorance, and regardless, evolutionary theory aptly provides an explanation for the evolution of the few examples he gives. So, logically, Behe’s argument falls pretty flat. But what about scientifically?

If, as Behe hypothesizes, biological systems are, in fact, irreducibly complex, then we should be able to see overwhelming evidence from scientific investigation. This is where the rubber meets the road, basically. Anyone can have an idea, but without rigorous, scientific investigation, peer-reviewed and published, that idea is just an idea- and can not be treated with any scientific respect. So sure, Michael Behe has the same academic credentials as Ken Miller, but has he been able to put his grant money where his mouth is? In other words, what scientific papers have been published that support Irreducible Complexity? Or, for that matter, Intelligent Design or Creationism in general?

Let’s just take a brief sample- on PubMed, one of the most popular biomedical search engines, a search for “evolution” turns up 178,160 papers. A search for “creationism” on the other hand, yields only 48 articles. Most of those are editorial articles by scientists expressing the concern over the creation vs evolution debate in popular culture. There is one interesting scientific paper that comes up, published in the journal “Laterality,” which concludes that people with a strong preference for one hand versus the other are more likely to believe in creationism, whereas people who are ambidextrous, or those who can use both their right or left hand, are more likely to accept evolutionary theory. A search for intelligent design brings up the same small numbers. But aside from that, there is no published data that can be easily found, no primary data that leads to the conclusion: creationism is the accepted hypothesis.

Fortunately, the Discovery Institute (the most scientifically rigorous Creationist organization of which I'm aware) has helped to resolve this issue by publishing a list of peer-reviewed literature supporting ID. I should, before I proceed further, explain what “peer-review” means. Essentially, this means that once a paper has been written containing new hypotheses, data, and conclusions, it has to be given to one or more “peers”, i.e., other scientists who are also publishing data, preferably in a field close to the one that the paper in question deals with. According to the Discovery Institute, the reason for highlighting a “peer-reviewed” list of articles is due to the fact that “critics of intelligent design often claim that design advocates don’t publish their work in appropriate scientific literature. For example, Barbara Forrest, a philosophy professor at Southeastern Louisiana University, was quoted in USA Today (March 25, 2005) that design theorists ‘aren’t published because they don’t have scientific data.’”

Well, let’s see the data!

They begin by showing seven "featured" articles. However, all of them are reviews, or position papers. None of them contain any basic research, and I'm unsure why they would want to "feature" them. Most of them are published in "Proceedings of" journals, which have a slightly different peer review process than other journals. Basically, as long as you can get a member of that particular society to sponsor your paper, it'll be published. The one contribution by Jonathan Wells would seem to be interesting, in that it proposes an experiment, but doesn't actually carry it out. I can't find any follow up papers, and it appears that it was just an abstract that was presented at a conference.

They likely realize that seven articles, none of which present any basic research, seems kind of weak, so they fill out the list categorically, starting with four "peer-reviewed" books. I'm not completely sure how these University presses work, but I very much doubt its anything similar to the review process for scientific articles. There's also three books that are "supportive" of ID, although not peer-reviewed (again, what does that mean?)

And finally we're down to the real meat, articles published in peer-reviewed scientific journals. Here we're down to six, only two of which were "featured" above. The first is in the journal "Chaos, Solitons, and Fractals." The second is in a "Proceedings" journal, and actually caused quite a stink from that society towards the editor who allowed its publication. The third is actually by Behe and is from a respectable journal, Protein Science, although it received a lengthy rebuttal in that same journal which basically showed that they had made several mistakes in assumptions for their calculations (Behe had tried to use mathematical modeling to show that mutations couldn't accrue fast enough to result in modification).The fourth is a review that questions the relevance of transposons to evolution (but not supportive of ID).The fifth is published in the "International Journal of Fuzzy Systems." And the last is in the "Journal of Theoretical Biology," postulating that the limited and predictive arrangement of protein folds represents a manifestation of "Natural Law," as opposed to "natural selection." This is not contary to evolutionary theory, however, since evolution does not predict that chemical interactions between amino acids change over time, just the arrangements of amino acids in a peptide chain, in response to varying levels of environmental selection.

Following these is a list of seven articles published in "peer reviewed" anthology books, five of which were published by members of the Discovery Institute. And then they have another seven "peer-edited" articles, four of which were also written by DI members. And they round it off with five philosophical papers, (with the guarantee of no basic research) one by Behe and the rest by William Lane Craig.

So that's it. The most the Discovery Institute can muster is 26 articles (none with a single experiment) and four books. As a point of contrast, remember there are 178,160 articles (25,672 of which are reviews) on PubMed which involve evolution (and that only goes back to 1916).

I want to repeat- not a single experiment has been published to test a hypothesis advanced by creationism or intelligent design. Not a single one. So sure, there are definitely scientists with real degrees out there, talking about intelligent design, but they can’t perform a single experiment to back up their arguments. Remember that next time you find yourself torn between two “experts” in the creationism/evolution debate. Firstly, there is no scientific debate on the subject- we can see that in the constant and overwhelming asymmetry of papers published in support of evolution versus those published in support of creationism. When less than 0.01% of the papers published on a topic are in support of an alternative explanation, you can pretty much guarantee that there’s no debate. And secondly, there’s just no evidence to support any other hypothesis but evolution. Not a single experiment. Which makes complete sense, of course- how can you hope to conduct an experiment to test a phenomenon which is, ultimately, supernatural? Those who would deny the fact of evolution know this, which is why the only arguments they can hope to get away with are those that attempt to discredit evolutionary theory. Remember- if an “expert” has no direct evidence in support of his own position, but can only attempt to tear down the opposing position, you can reasonably conclude that he doesn’t have anything meaningful to offer.

So, in conclusion, evolutionary theory is the only explanation for the data that is available to us, and no alternative hypothesis (creationism, intelligent design, etc) even has the power to propose a single experiment which could support it. I think it should be pretty clear now that, for those inexperienced with evolutionary theory, choosing the experts to listen to should be a no-brainer. Thanks for listening, and take care.