Questions for PZ Myers

Learn more about my research In February and March of 2009, PZ Myers answered visitors questions about evolution.

Your Comments, Thoughts, Questions, Ideas

Jay Kanta's picture
Jay Kanta says:

Does radioactivity cause genetic mutations at the DNA level, and if so, can radioactivity account for some of the diversity of species?

posted on Mon, 02/23/2009 - 12:01pm
PZ Myers's picture
PZ Myers says:

Mutations are ultimately the source of all novel genetic variants, so yes, the accumulation of differing genetic sequences in different lineages does lead to species variation.

Radiation does increase the mutation rate. Ionizing radiation striking a molecule can break it, causing cellular repair mechanisms to try and fix it, but sometimes they insert the wrong bases in the broken section. If this damage occurs in your gonads, it can produce mutations that will be passed on to the next generation. If it occurs in other cells in your body, it can lead to cancers. We know for a fact, for instance, that cancer rates in areas with high levels of background radiation are higher than in places with less radiation.

However, radioactivity is not the sole source of mutations! The most common cause is probably simple copying errors; every time one of your cells divides, every one of the 3 billion bases in your DNA must be accurately duplicated. There is no such thing as a perfect enzyme, and sometimes they slip up and make a mistake. Other causes are chemicals which can damage DNA -- our own bodies, as part of metabolism, can produce reactive molecules called free radicals that can damage DNA if they aren't cleaned up, and you also may be exposed to mutagens (chemicals that can cause mutations) in your environment.

Don't panic, though. Mutations are a normal hazard of our existence, and they occur in all of us at a low level. Most are neutral and harmless. Do take normal precautions, of course; when you get X-rays, your doctor will limit your dose of radiation as much as he can, and you shouldn't go around eating toxic waste, and avoid sitting on used nuclear fuel rods.

posted on Mon, 02/23/2009 - 6:41pm
bryan kennedy's picture

Have you played or heard of the video game Spore. It was purported to be a fun way to play with some evolution concepts, like a SimEvloution instead of SimCity (it was actually made by the creator of SimCity).

What do you think of attempts to playfully learn about evolution?

posted on Mon, 02/23/2009 - 12:07pm
PZ Myers's picture
PZ Myers says:

Yes, I have! Electronic Arts (the company that created the game) even sent me a pre-release version of the Creature Creator so I could try it out.

As a game, I thought it was fun, although it wasn't actually my favorite kind of game. I played it a few times when it first came out, but haven't tried it since. But of course everyone will like different kinds of games, so I'm sure there are many people who enjoy it more than I did.

As a model of evolution, though, I thought it was very poor...which probably contributed to my waning interest. Evolution isn't about achieving a goal, like getting to the point where a species builds spaceships, which means, I think, that a game that accurately modeled evolution wouldn't be much fun to play! It would have to depend much, much more on chance, it would take a very long time, and you'd never get results that the player actually wanted.

There are computer models of evolution out on the web that people can tinker with; some examples are Tierra and Avida. They don't much resemble a game, though, but are more like technical simulators of the process. They are still cool to tinker with, and actually teach us much about how evolution works.

posted on Mon, 02/23/2009 - 6:18pm
Anonymous's picture
Anonymous says:

Are humans still evolving? What selective pressures do you think are most strongly influencing the direction of our evolution? What research, if any, has been done on this question?

posted on Mon, 02/23/2009 - 1:35pm
Charley's picture
Charley says:

Why do large animals live longer than small animals?

posted on Mon, 02/23/2009 - 1:35pm
Dan Isaacs's picture
Dan Isaacs says:

Hi PZ, what is your favorite Octopus (or cephlapod), and why?

Thanks!

posted on Mon, 02/23/2009 - 1:47pm
PZ Myers's picture
PZ Myers says:

I can't pick a favorite. I like them all, and each one has its own unique attributes that make them special.

posted on Fri, 03/06/2009 - 10:13am
Marc Abian's picture
Marc Abian says:

In situations where a group of the same organism has to co-operate what's to stop one member mooching off the work of the others? If he could reap the same benefit but not have to put in the same amount of work, then that trait would desirable in the short term and eventually the become dominant and that the group would perish. Of course, the continued existence of such arrangements shows that this does not happen. Why not?

posted on Mon, 02/23/2009 - 2:45pm
John Mac's picture
John Mac says:

Hey PZ,

I'm a primary-school teacher in Ireland, and although evolution doesn't feature strongly in our science curriculum, at least not for under-12's, I'm keen to provide as much accurate information as I can, as clearly as I can - so I'm more than willing to risk a spectacular display of ignorance in search of a better grasp of this fascinating subject!

I understand the basic concept of evolution (I think!): when a random change in the genetic code of an organism leads to a beneficial change in that organism, the odds of that organism surviving and reproducing, thereby passing on that beneficial change, increase.

An example I sometimes use in class is that of the whale, which evolved from a land animal, with its nose on the front of its head, to a sea-based animal, with its nose on the top of the head. The change in the position of the nose was, as I understand, gradual. Does this mean that, over many generations, many random mutations were required, all of which related to the position of the nose, like lightning striking the same place over and over? Is that part of the reason why evolution is such a slow process? Or is there something else going on - like a tendency for mutations to occur again in the same part of the genome if there has been mutation there in a previous generation?

Thanks PZ, I'll leave you with an old Irish saying: bail ó Dhia ar an obair. Probably best I don't translate....!

John.

posted on Mon, 02/23/2009 - 3:00pm
PZ Myers's picture
PZ Myers says:

The change in the position of the whale's nose was gradual, and is even preserved in the fossil record. It even has a name: nasal drift. We can see that older fossils had nostrils far forward, and that over time, they creep farther and farther back.

This wasn't because there was special frequent mutation in just that part of the genome responsible for nose position. There are mutations happening all over the place, and large amounts of variation in various features occur all the time. Most of this variation is not significant; in special situations, it may become significant and part of the range of variation selected for.

Think about human noses. We don't have the same noses, but instead, we have a variety of sizes and shapes. These are a consequence of genetic (and some environmental) variation.

It was the same with ancestral whales. There were small variations in exactly where the nostrils formed, and for the most part, this was not a big deal. However, when they began to spend more and more time in the water, the animals with the nostrils a little farther back in the head found it easier to catch a breath, and they did a little better job of surviving. The next generation would have inherited nostrils located slightly farther back.

However, that doesn't mean that all at once they all had nostrils 5 millimeters farther back! The average position of nostrils would be moved, but there would still be some individuals with nostrils a bit more forward, and some with nostrils a bit farther back still. Evolution would select for those at the most advantageous position, and produce another generation with an average backward shift, but still with a cloud of variation in the precise position.

So the first of your explanations is the best answer, but it doesn't require some unusual preference for lightning to strike in a particular place. All it takes is a broad pool of variation, and selection slowly takes the variants that work best in particular conditions.

posted on Fri, 03/06/2009 - 10:28am
arensb's picture
arensb says:

Let's say you have a series of fossils showing change in a species (or series of species) over time. How can you determine that the change was caused by natural selection, as opposed to some other mechanism, like genetic drift?

Basically, how can we detect natural selection (as opposed to other mechanisms of evolution) in the fossil record?

posted on Mon, 02/23/2009 - 3:45pm
Ann Braden's picture
Ann Braden says:

Maybe I missed this back in 9th grade biology (c. 1967) when we studied evolution--and I'm embarrassed to be asking a question that probably has an obvious answer-- but WHY were the dinosaurs and so many other ancient critters--even mammals and birds-- so huge? (Titanaboa is a newly discovered case in point.) Why did they evolve into such super-sized critters--and yet after they died out they didn't re-evolve into big creatures again? I can't figure out what the evolutionary advantages of being so enormous would be. Except for whales and elephants and some NBA players, doesn't size matter any more?

posted on Mon, 02/23/2009 - 4:09pm
PZ Myers's picture
PZ Myers says:

They didn't! What you're experiencing is selective vision.

At the same time that those animals on the large end of the scale were thriving, there were many, many more that were small. Large animals are more likely to fossilize, though, so their remains tend to last longer, and we also have this psychological bias to be more impressed by the largest things we find, so they loom larger still in our mind. But if you actually look at all of the fossils excavated from an ancient mammal site, for instance, what you may find are a few huge titanotheres that get all the press, but at the same time there will be swarms of tiny little rodent teeth that are mostly ignored.

As for why animals would grow large at all, there are a couple of good reasons. One is that it's a way to escape predators -- if you are very much larger than something that wants to eat you, that can be usefully intimidating. That means there is a kind of race among some prey animals to avoid predation by growing too large to be vulnerable. Another is to exploit new food sources. A mouse is going to have a tough time eating food found on the tips of tree branches, but a giraffe can reach them easily.

There are downsides to growing large, though. The biggest is that it requires enormous amounts of energy, and it also makes you vulnerable to fluctuations in food resources -- it's no good being huge if there isn't enough to eat! So some animals grow to a large size that is at the limit of food availability, and are more susceptible to extinction...but they do great while the eatin' is good.

That's also why animals from some eras are so much larger than what we're accustomed to: they lived at times when overall energy availability was greater. Titanoboa is a perfect example. It lived in an exceptionally lush, warm tropical region and time, and snakes that size would die today because it is too cold and the ecosystems aren't quite rich enough to provide as much food as was available then.

posted on Fri, 03/06/2009 - 10:42am
Steve S's picture
Steve S says:

Dr. Meyers, sometimes features on an animal appear counterintuitive, like the photoreceptors in the human eye in place "upside down" as it were. There are many such examples. Do you have any favorites?

posted on Mon, 02/23/2009 - 4:25pm
Happy Cetacean's picture
Happy Cetacean says:

Dr. Myers,

My question is regarding a part of the theory of evolution called common descent. Common descent says that all life on this planet descended from a single common ancestor that lived 3.8 billion years ago.

Does that literally mean that there was only one original instance of life on this planet and that all life descended from that organism, or were there multiple starts and stops of life coming about on this planet, but only one of those survived?

The heart of my question would be to ask why would we have only a single starting point? Why not have multiple instances of life coming about on this planet, and each of those then evolving to form the diversity we see today.

Please provide some clarity around this.

Thank you sir.

Sincerely,

Happy Cetacean

posted on Mon, 02/23/2009 - 4:46pm
Matt Schoeneberger's picture

Dr. Myers, is there a study of evolution as projected into the future? Can we predict future beneficial mutations that might allow for an organism to carry on? If so, can we apply this to ourselves and how might it help us?

posted on Mon, 02/23/2009 - 6:17pm
shanai's picture
shanai says:

What do you think about the studies that suggest human evolution has been speeding up over the past 40,000 years? And what does that even mean?

posted on Mon, 02/23/2009 - 8:19pm
Enigma32's picture
Enigma32 says:

At what point do a collection of similar mutations within a group become a totally different species, separate from the species that they originally manifested in?

posted on Mon, 02/23/2009 - 8:30pm
arensb's picture
arensb says:

If you had a series of well-preserved fossils showing change in species over time, would it be possible to determine that the change was due to natural selection, as opposed to some other mechanism, like genetic drift?

posted on Tue, 02/24/2009 - 12:14am
Ian James Anthony's picture
Ian James Anthony says:

Could you help me differentiate some terms? As I understand it, evolution, or genetic change over time, is a fact. The theory of natural selection is our best explanation as to why this occurs. Is this correct? Moreover, can evolution ever become a law? Are there biological laws?

posted on Tue, 02/24/2009 - 2:16am
PZ Myers's picture
PZ Myers says:

Yes, evolution is a fact. We have observed it in the lab and field, and in the fossil record, so yes, species change over time.

Genetic change over time is also a fact. That is also a very broad definition of evolution.

The theory of natural selection is actually not the best explanation of evolution, as defined above! Many mutations occur all the time, most are neutral in effect, and this is almost certainly the predominant factor in evolutionary change. We would have "genetic change over time" even in the complete absence of selection!

Selection is the best explanation for adaptive change, that is, change that produces more offspring that have functional advantages.

Scientific laws are odd beasts. There is a common misperception that there is some kind of hierarchy, where hypothesis becomes theory becomes law, with law being the best and strongest. This is not true!

Scientific laws, like Ohm's law or Boyle's Ideal Gas Law, tend to be mathematical descriptions of very specific, reduced phenomena, like the flow of electrons in a wire or the relationship between volume and pressure. They are powerful and useful tools for breaking down and studying more complex events.

Scientific theories are altogether different. They integrate and explain collections of observations and even laws and put them together into an explanatory framework that helps guide research and make predictions. They tend to tie together much more diverse and complex elements than a law can.

There are biological laws within evolutionary theory: for instance, the Hardy-Weinberg law describes the expected distribution of alleles in a population that is not undergoing selection. Theories do not become laws, in general, and laws do not become theories -- they are usually very different kinds of explanations.

posted on Fri, 03/06/2009 - 10:56am
Anonymous's picture
Anonymous says:

Could you please tell me about the status of Rupert Sheldrake, whose take on evolution is neither Darwinian or Creationist. He wrote several books in the 80's about zones of "morphoegenic resonance" and I just need to ask, is he a crank, or is he taken seriously? Thanks

posted on Tue, 02/24/2009 - 8:55am
Anonymous's picture
Anonymous says:

is the humbolt squid really taking over the pacific??

posted on Tue, 02/24/2009 - 12:50pm
JGordon's picture
JGordon says:

Hi PZ

I'm answering some random questions from the museum floor for the Science Buzz blog, and this one was at the top of my stack: "Why can't boys have babies?"

I suppose the obvious answer is that we just haven't got, you know, the plumbing for it. But that's sort like saying "boys can't have babies because boys can't have babies." I thought you might be able to provide some more insight here—how did internal fertilization evolve? And why is it that just one sex carries developing offspring? Why is it usually the female? And why, in cases like the seahorse, is it sometimes not the female?

Thanks!

posted on Fri, 02/27/2009 - 1:13pm
PZ Myers's picture
PZ Myers says:

At first, sexual reproduction was simple. Multicellular organisms just shed a few haploid cells called gametes into the environment, the gametes found other gametes, fused, and started growing into another adult. You didn't have boys and girls, because both did the same thing, and neither had special responsibilities.

Then came another innovation: mating types. This probably evolved first as a mechanism to prevent gametes from fusing with gametes from the same parent, but it had the effect of creating what we would sort of call multiple sexes, although at first they probably all still did the same thing.

Another advantage in evolution for some organisms is parental investment. Rather than just throwing gametes out willy-nilly to sink or swim entirely on their own, some species gave their progeny a little advantage: by packing the gametes full of nutrients that would allow them to grow a bit faster, they could outproduce less caring parents.

This has been an increasing trend in some lineages, giving offspring a leg up by investing more and more care in their early growth. Mammals and humans are far out there on the spectrum -- we shelter the developing embryo in our bodies for months, and then we care for the infant for years, and then we protect the children and adolescents for years after that, until we're fairly confident they can live on their own. We evolved this property because parents who took care of their kids for long periods of time produced more children who survived to adulthood than parents who threw their children out into the cold cruel world at an earlier age.

That's how internal fertilization evolved, as part of the process of increasing parental investment. If one parent is holding its gametes inside its body to protect them, the other parent has to get its gametes into that body for fertilization to occur.

As for why boys don't have babies, it's a matter of specialization. Males have body parts to facilitate getting gametes into females, and females have body parts to promote growth of embryos. We each have our job to do.

Of course, its the females who are stuck with the most work in nourishing a baby. Some species have sexes with both specializations, and are hermaphroditic. In some of those species, such as sea slugs, mating is more like fighting, with each competing to see who can insert a penis first -- the winner just gets to reproduce with cheap sperm, while the loser has to go to all the work of laying eggs!

posted on Fri, 03/06/2009 - 10:11am
Anonymous's picture
Anonymous says:

Will humans continue to evolve?

posted on Mon, 03/16/2009 - 12:18pm