Carl Sagan on the Timescale of Evolution

Comment by: Karen

That’s so brilliant! He kind of took “Ancestor’s Tale” and condensed it down into 5 minutes. :-)

The feeling of awe that inspires (”we are made of star stuff!”) is exactly what I try to convey to people who contend that without religion there’s no mystery, joy or wonder in life. Au contraire.

Comment by: Ir (Helen)

That’s nicely done.

I really like Carl Sagan’s book The Demon Haunted World; since I read that I’ve been impressed with him.

Comment by: Karen

I watched it and the whole time, I was thinking “but how? What caused it? Why did this change to that, or that change into this? Why when the star first exploded didn’t it destroy the life it seems to have started? If it happened again it would destroy life that exists as we know it. Why did the fish come out of the water? Why did it get hairy instead of staying scaley? Why why why. A much too simplistic approach, I know. But that’s where I’m at with it … a very simplistic doubter.

Mike there’s a pretty good one-hour show running this very weekend on the National Geographic Channel called “Was Darwin Wrong?” I caught it last night (while folding laundry).

It certainly doesn’t have the grandeur or the literacy of Carl Sagan’s inspired prose, but it does give a solid explanation of evolutionary theory with pretty good illustrations.

More importantly, it goes through half a dozen of the most-common creationist claims about how the theory is flawed and shows explicitly how the theory stands up to those supposed “flaws.” From the age of the universe, to the evolution of the eye, to transitional fossils and genetic mutations, it’s very up-to-date and introduces scientists from all over the world who talk about the actual research they have done on those areas.

It’s going to be on tonight Friday, December 8, 1 a.m. and Sunday, December 10, 5 p.m. I’m going to tape it and I’ll be happy to send you the videotape if you want to see it and can’t catch it this weekend or don’t have cable.

Comment by: Mike O

I have satellite and the ability to record it. I’ll record it … that might help a bit.

Comment by: Siamang

Our current understanding is that the earliest life forms appeared about 4 billion years ago. So I’ll put that out there for a second before hitting your main question.

let’s say for the sake of argument that there have been 2.25 billion different kinds of plants and animals so far in the past 2.25 billion years, that means we have averaged 1 new species of plant or animal per year. And let’s say 1/2 billion of them are still alive today.

I’d like to know where you’re getting these numbers. I can’t quite get my head around your question without knowing what you’re counting. Do you know how many species are alive today? And are you counting only megaflora and megafauna, or microscopic things as well?

Anyway, some help on your numbers would help me give you a specific answer to what you’re seeing.

Shouldn’t we be seing an explosion of new life forms the longer the evolution process goes on?

Who says we’re not!?! According to the fossil record, we’re seeing many more new species!
Check out this image for a graph. It’s a bonanza!

http://upload.wikimedia.org/wikipedia/en/a/a5/Phanerozoic_Biodiversity.png

That growth trend may be partly do to the fact that we can more easily find and catalogue the more recent fossils. So we’ll put that caviat with that graph, in the interest of intellectual honesty.

Let’s say that graph is correct, and we’re getting more species now than we did way back ago. Greater and greater biodiversity.

But that doesn’t mean evolution is more rapid. It’s still a slow process. Yes, there’s greater diversity now. We have more species now than in earlier times.

That’s not the same thing as making evolution of individual species more rapid. It just means that there are more new species.

It seems that at this point with so many things that could possible mutate tomorrow, that we should be seeing spontaneous species regularly, but we aren’t, are we?

I want to caution you at this point. Evolution doesn’t mean that an antelope suddenly gives birth to a moose. Every creature gives birth to offspring of their same species.

Making a new species takes hundreds or thousands of generations. That didn’t speed up. It’ll take thousands of generations of isolation before a puppy from an isolated line of Canus Domesticus can no longer breed with a Golden Retriever.

No particular organism’s speciation sped up just because the world is full of more and different animals than ever before.

Here’s an analogy. You know the old saying “Nine women can’t have a baby in one month”?

It’s a good old phrase, because it tells us that some things can’t be rushed. Even if you add more people, you can’t hurry it up.

Yes, nine women can’t have a baby in a month. If you really plan things, you might be able to have each one of them have a baby so that they give you an average of one baby a month.

Well, same thing with evolution. Yes, with more biodiversity, there are more new species coming from new species.

BUT, that doesn’t mean that evolution happens any faster, only it’s happening in more places at the same time.

And with most animals, evolution happens way, way too slow for us poor humans to watch it. That’s the downside of being products of evolution. Evolution takes generations and generations and generations… and we’re long dead before we see any changes.

Comment by: Eliza

This 2004 msnbc article is interesting, talks about the rate of discovery of new species in the oceans (not the same as the rate of new speciation, of course!).

Siamang’s right about how slow the process is. I think it was Dawkins who pointed out that every being is a “transitional” organism, or at least has the potential to be - it depends where that branch of the family tree ends up, hundreds and thousands of generations later, tiny change upon tiny change.

Remember too that there’s no reason for evolution to be occurring at the same rate, all the time. New species are more likely to come about when there’s an environmental niche that can be filled, that’s not already filled with competitors and predators. For example, when old species have been decimated somehow, new species can “move in” - so, mammals were all small until after the dinosaurs - then mammals were able to become larger, didn’t instantly become dinosaur food! Or, didn’t have to compete with the dinosaurs for food/prey. Or, when a new environmental niche forms, species that can thrive there (or, at least, survive there) can “move in”. For example, it’s been observed that some bacteria can now metabolize nylon, a man-made polymer - they’ve developed new enzymes, or actually mutated variations of old enzymes!

With the poles (and the rest of the earth) warming up recently, Emperor penguins (South pole) and polar bears (North pole) are declining in number. This is happening fast enough that they could go extinct. If they don’t, the few that remain may have some characteristic different from the prior “norm” for their species, something that allows them to find food, shelter, breeding grounds, etc despite the climate change. That different characteristic will be passed along to their offspring, and any changes that strengthen that characteristic, or add to the ability to eke out an existence in hostile territory, will be selected for. (Not that we’re likely to see a recognizably new species develop before our eyes; as Siamang said, that takes a looooong time.)

Or, more likely, Emperor penguins and polar bears will become extinct, and some other animal will migrate into their territory and take over their changed environmental niche. (I hear there used to be crocodiles at the poles…maybe that will happen again.)

Comment by: cautiousmaniac

You know the old saying “Nine women can’t have a baby in one month”?

I gotta say I’ve never heard that saying. I might not be old enough.

In the interests of caveats, I offer further caveats.

Firstly, species limits are one of the fuzziest issues in evolutionary biology, which is highly ironic since we’re supposed to be dealing with the origins of species. While it’s very obvious that a cat and a dog are different species, something akin to horses and donkeys are much less distinctive. Even more infuriating (…to people who like clear-cut answers) are animals which seem to be distinctive species which can mate and produce viable offspring.

Example: Ensatina

This is a case of several morphologically distinct salamanders (And when I say distinct I mean they are gorgeous and I’m pretty bummed that I have yet to see one) which inhabit slightly different geographical ranges. The problem that occurs is: along the borders of the ranges, animals of what would look like different species mate and produce viable offspring.(1)

Are we supposed to call them subspecies? Or are they animals that are beginning to speciate? Or are they ring species that never fully evolved reproductive isolation and are now re-meeting and thus hybridizing? Are hybirds totally natural but rare because they aren’t as well adapted as their parental species are? It’s in all truth a scientific work in progress, that some of today’s molecular systematic herpetologists dream of solving.

…and this is in extant animals! One of the main questions driving my current research project is trying to decipher how many species are present in my study group, and all I have to look at is what was “lucky” enough to fossilze.

We can never get the true honest count of species on this planet at this moment in time or, even more maddening, in the past. Which brings me to

Second caveat: this graph (http://upload.wikimedia.org/wikipedia/en/a/a5/Phanerozoic_Biodiversity.png) is loaded with caveats. All it’s intending to show is the diversity of marine macroscopic invertebrates (at a generic level) fossilized since the beginning of the Cambrian until Recent times.

Organisms which are not animals/lack hard parts/live on land/possess backbones are ignored by the diversity curve. So I’m really trepiditious about assuming that the trends it shows are related to trends of all life.

Comment by: Mike O

Oops, one more thing … I realized yesterday that the questions I’m asking are not intended to question the evidence that exists, but rather introduce new evidence (math, history, circumstantial, etc) into the equation. The data is the data, I can’t dispute that. But there’s more inputs that I’m questioning … mathematics in this case.

Comment by: cautiousmaniac

Eliza’s mentioning of situs inversus reminds me of the book Mutants, which I refuse to give enough praise to. And her handling of Mike’s question is very good. I want to throw in more input but I’m not really very coherent right now (…if I ever am)

but it seems to me that conceptually or logically, we should be able to see things in mid process

I think we are seeing things (organisms) in mid-process. We are, whether we like it or not, acting as a force in the world that is affecting the evolution of other organisms. Organisms with short generation spans (eg bacteria) have evolved resistances to drugs that we over-use. Population genetics studies of species that we are over-harvesting (eg whales) indicate that these species are reproducing at earlier ages than “normal” (although this is of course challenged by whaling countries who refuse to accept responsibility…) Species that are able to survive in civilization are thriving (rats and pigeons) and those that aren’t join the dodo and the Stellar’s sea cow.

I think that our potential to cause intense, but relatively short-term, damage to the biosphere and atmosphere will cause all kinds of evolutionary responses by organisms. Not only by opening up tons of new niche spaces (by extinctions caused by us) but also through the re-shuffling of terrestrial and marine food chains that we are doing. Cephalopods might, even if only temporarily, really enjoy our addition of carbon dioxide into the atmosphere.

Comment by: Karen

Re the question about whether we can “see” evolution occurring: Yes. It’s in the human genome, which scientists are starting to unlock just in the last couple of years. (This is why science is SO exciting! There are new discoveries being made all the time.)

There’s an article in today’s NY Times that talks about how lactose tolerance evolved several times in isolated populations over the last few thousand years. Tolerance for adults to digest milk was a mutation that allowed individuals in dairy-herding societies to thrive on the extra calories found in lactose as well as get extra fluid during droughts. Those who didn’t have the mutation died out much more quickly and left fewer descendants.

A surprisingly recent instance of human evolution has been detected among the peoples of East Africa. It is the ability to digest milk in adulthood, conferred by genetic changes that occurred as recently as 3,000 years ago, a team of geneticists has found.

The finding is a striking example of a cultural practice — the raising of dairy cattle — feeding back into the human genome. It also seems to be one of the first instances of convergent human evolution to be documented at the genetic level. Convergent evolution refers to two or more populations acquiring the same trait independently.

Throughout most of human history, the ability to digest lactose, the principal sugar of milk, has been switched off after weaning because the lactase enzyme that breaks the sugar apart is no longer needed. But when cattle were first domesticated 9,000 years ago and people later started to consume their milk as well as their meat, natural selection would have favored anyone with a mutation that kept the lactase gene switched on.

Such a mutation is known to have arisen among an early cattle-raising people, the Funnel Beaker culture, which flourished 5,000 to 6,000 years ago in north-central Europe. People with a persistently active lactase gene have no problem digesting milk and are said to be lactose tolerant.

Almost all Dutch people and 99 percent of Swedes are lactose tolerant, but the mutation becomes progressively less common in Europeans who live at increasing distances from the ancient Funnel Beaker region.

Comment by: Siamang

Oh, and nothing “sprouts” a feature in anticipation of a future need.

Things that get wings make them out of limbs. The bat didn’t sprout wings. It slowly developed, over lots and lots of generations, its front arms into wings. It didn’t suddenly fly. It crawled and climbed. Then it was probably a leaper. Then a glider, like a flying squirrel, and eventually a better and better glider. Then a flapper. All of this was small, small, steps. Getting slightly better over hundreds or thousands of generations.

Same with birds. The front arms of dinosaurs became the wings of birds.

Small, gradual steps. It is only when looking back with hindsight that we humans think of them as being intermediates. Nature doesn’t treat any animal as an intermediate. Nature has no such purpose.

Comment by: cautiousmaniac

Oh, unrelated to Carl Sagan (except in the sense that he is an extinct organism), but Yangtze river dolphins are probably totally dead.

Making them the first whale species we have been able to kill off (although some cetologists disagree on whether there’s already been one we killed off).

Comment by: MTran

The real scientists on this board can probably provide better details on this but I thought you might want to consider a few notions that don’t get a lot of media attention.

The first is that “mutations” or other developments can be “invisible.” By that I mean some changes to an organism may not give any external indications of their existence. So that a creature with more effective healing mechanisms, or more efficient respiration, may simply seem to live a bit longer or look healthier or happier. But the cause may be a simple change in the appearance of an alternate gene expression or novel alleles. Physiological as opposed to anatomical changes are not always so easy to abserve. Behavioral changes may be subtle or obvious but we may not be able to see them except under special circumstances.

The second idea is that even if an induvidual develops a “mutation” or novel feature, that new trait may not be passed on to offspring, thus it can disappear from the gene pool even if it is advantageous.

A third notion that I find quite interesting is the idea that human beings have broken out of our ancestral niche restrictions. Humans are no longer dependent only on sheer survival skills or attributes within a narrow zone of habitability. We now inhabit every conceivable zone of earth, regardless of temperature or water availability. Anywhere that another species can survive, so, apparently, can we, omvivorous toolmakers that we are. Some have proposed that by jumping from “a” nich into the world at large (and even the moon and space station) humans have substantially reduced naturally occuring evolutionary pressures. This is an idea that I would like to see explicated further. If anyone has any texts they can refer me to, I’d be happy to read them.

One final comment: I hear with some regularity that modern medicine and cultures are allowing previously “unfit” people to survive and reproduce, allegedly leading to a “less fit” human population. I don’t care for some of the assumptions that go along with that idea. It may be true that people who would not have survived childhood in the not so distant past can do so now. That this is somehow negative just doesn’t agree with me. Accident, starvation, and disease killed off countless strong, intelligent, otherwise healthy people for countless millenia. That we are no longer subject to the winds of misfortune to the same extent as our ancestors were is a benefit, as far as I’m concerned. Plenty of seriously disabled people are quite capable of activities that ancient humans couldn’t imagine. Software designers, poets, radio announcers, countless other occupations no longer require a physically strong body, just a good head and willing spirit. And even if we do find that there are children born who would not have survived in 1950 let alone 1500 or 15,000 years ago, I tend to see that as a good thing for society and not a bad thing at all.

Comment by: Siamang

It was a heck of a lot easier to feed 2 billion mouths than the current 6 billion

I would ask the question: was it?

It’s not automatically the case. We may have gotten better at feeding people in the meanwhile. I’d like to know the numbers.

With technological and economic advancement in China and India, for example, I have the impression that a lesser percentage of the human population is malnourished.

I may be wrong about that. What are the numbers?

Comment by: Siamang

I’m in awe at your ability to find those data.

I looked and gave up. I had the impression that we were better as a proportion. But better in absolute terms as well… that IS progress!

I don’t know the carrying capacity of the earth. Obviously we’re already having a damaging impact.

To those who think the bad will continue to magnify, or those conversely who think the past progress indicates future human stability, I’d offer the caveat given to all freshmen sociologists: beware the permenant trend.

I suspect far more factors are at work, and we may in a generation or two be worrying about a population dip.

Comment by: MTran

Siamang said: I’m in awe at your ability to find those data.

Yeah, me too!

I think overpopulation is a very real problem yet one that sensible people could prevent if they wanted to. Of course, there are millions of people who don’t take simple precautions to avoid contracting HIV. If we can’t convince people to save their own lives, how can we convince them to behave in reproductively responsible ways?

The toll on the environment from such a large human population is pretty hefty. There are some (though few) reasons to hope that we can make some progress against the rate of population increase. From what I’ve read (please don’t make me look up the actual statistics, I’m tired!) it appears that there is more than enough food to feed everyone on this planet.

The primary barriers to adequate nutrition are no longer agricultural or technological but political. At least, that’s what I’ve read somewhere or other. Now it may be that the people making those assertions are doing so for political reasons but I’ve been pretty much convinced that it is a largely political ineptitude and corruption problem.

Also, there appears to be a consistent trend for family size to decrease as populations shift from farm and village to cities and industrial / technological economies. So perhaps we will soon reach our maximum growth and reach a healthier stability.

As far as “unfit” people “weakening” the human species, I just don’t see that happening in large enough numbers to make me concerned at this point. I may be misreading things, though.

Many people who are “unfit” at birth are the victims of developmental or environmental effects rather than carriers of heritable genetic conditions. I think that these non-genentic but congenital problems get lumped into the wrong category at times in some discussions. But I also think there are enough bio and medical people an this site to keep that sort of confusion at bay.

Comment by: cautiousmaniac

Firstly, thank you to whoever improved this blog. It’s taking me a bit of time to get used to but comments now rock the kasbah.

Siamang, if in 20 or 40 years I’m worrying about a population dip, then the world will have changed dramatically between now and then. It’s not impossible, but the only ways that the world will have less people in the future than now all involve calamities that I’d rather the human species not suffer. If fresh water becomes too expensive to afford, if climate change happens suddenly and farming regions drastically shrink in size, if widespread coastal flooding due to glacial melt occurs, if fisheries around the world crash at a rate faster than expected, if oil somehow runs out, if monotypic food crops are decimated by pathogens, if any number of killer pathogens ever gets spread into a large population, if a big rock from space smacks into our planet, if the Terminator movies were actually prophetic… Any of these things could happen but I doubt without one (or a few) happening that the world will have less people in 2025 or 2045 than it does today. And, thinking about human age structuring, there will actually be more breeding-aged people in the future than now (unless human fertility patterns somehow drastically change) which invites the possibility that population growth will, unless stopped by food/energy supply, continue at faster rates.

World Population Prospects is a UN-ran website which includes several calculators wherein you can see their forecasts for population, (urban/rural/total) and population density in various regions (world vs individual continents/countries.) You can also look at four forecasts which use different rates of population growth; low, medium, high and “constant fertility”, in other words, children born into x-sized families will themselves breed x number of children children. Think of that as the “lack of education” model.

Since anyone can generate numbers with it, I’ll leave readers to do their own number-making. The only ones I want to post involve population density. The UN is taking two facts (current population size and the land area of continents) and then fitting past, current, and future potential populations to that land area. The US and Canada don’t see much of a change, in all reality (and all below numbers are in people / sq. km)

2005: 15
2050 low: 17
2050 medium: 20
2050 high: 23
2050 constant fertility: 21

Things to note are that 1) population density increases regardless of the amount of population growth 2) “constant fertility” is within the bounds of “medium” and “high” rates of growth because the number of children per couple in the US and Canada is relatively low.

Europe shrinks in population density, which is why Europe has an immigration issue similar to ours (people from developing countries are coming in to fill gaps in the workforce) but doesn’t have quite the same amount of legal/political stupidity about the issue that we do. (I was going to say that Europe doesn’t have the same amount of xenophobia but that would be ignoring some ugly realities.) Immigration is probably going to keep Europe at or above modern population sizes but is not factored in by the UN population growth calculator which is only considering [birth rate - death rate = population growth] rates.

Where’s the biggest problem? Well, to be blunt, Africa.

2005: 30
2050 low: 55
2050 medium: 64
2050 high: 74
2050 constant fertility: 102

Right now Africa has a population density twice as much as here in the US/Canada. This population density will (potentially) increase by somewhere between 25-44 people per sq. km of land. All of those numbers assume that people in Africa breed less than they do now. If Africa does not go through a massive educational project in which women are given equal rights and equal protection under the law, birth control is advocated and fiercely promoted, and adoption and other family planning strategies are taught and used, then the continent of Africa in 2050 will have 3 people per square kilometer for every 1 it has now.

Which to me says that if you have any plans to see African wildlife in the wild, do so now when it still exists.

Siamang is being skeptical here, which I can’t blame him for since if I start disliking skepticism than I’d start self-loathing. But I believe that human population has, primarily, two possible horrible future potentials: continuing to grow at a fast pace while raping the planet to do so, or hitting a brick wall (or several) and watching as our population “restores” itself to a more viable number through the wretched and miserable death and suffering of a whole lot of people.

I’d rather neither of those two options happen and so I want people to be more sustainable and less selfish in their thoughts and actions about reproduction. No offence is meant against breeders in the audience, but if you must breed, be smart, reasonable and sustainable about it. Just because a couple can make 10 kids doesn’t mean it is by any means a good idea.

Anyway! I spent way too much time yesterday (and today!) writing and reading for this, but not for upcoming deadlines. So I am going into a self-imposed work/school/research-related hibernation state. Be back after Solstice, warm holiday wishes to all, etc. etc.