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New species differentiate in far fewer generations than previously thought

By maynard in News
Thu Oct 19, 2000 at 07:07:45 PM EST
Tags: Science (all tags)
Science

University of Massachusetts postdoctoral researcher Andrew Hendry announced findings of speciation, or the splitting of one species off the branch of another, in far fewer generations than previously thought. Hendry's team saw evolutionary adaptations and reproductive isolation (meaning a new species) within twelve to fourteen generations of the sockeye salmon he was studying, or about sixty to seventy years.

Another study, led by Megan Higgie, of the University of Queensland, Australia, showed that Drosophila serrata , the standard fruit fly, increased their mate selectivity by changing pheromones in only nine generations to improve chances of finding and mating with the correct species. [note: this link includes information from the previous link]


An evolutionary ecologist, Dr. Hendry conducted a study of the sockeye salmon in the pacific northwest. His findings are published in the October 20th issue of the journal Science. Explaining speciation, Dr. Hendry states, "There is a widely-held perception that when one population splits into two different environments, traits evolve quickly and, as a result, the two new populations become less likely to interbreed. That is, they become reproductively isolated. This process, called ecological speciation, maybe one of the easiest and fastest ways that new species arise. Our results suggest that this perception may not only be correct, but in spades," said Hendry. "The classic examples of ecological speciation are for groups that have existed for 10,000 years. Even the fastest examples are for some insects over 200-400 generations. In these cases, we know reproductive isolation evolved sometime in the past, but we don't know how quickly."

According to the article, this is exactly what Dr. Hendry found, only far faster than previously expected. "Sockeye salmon bury their eggs and spawn in different kinds of locations, and in a variety of environments, even in a small system such as this," Hendry explained. "When new populations become established at different sites, you'd expect them to evolve different adaptations, and that's in fact what happened."

There are some wonderful photographs as well as a more detailed explanation at the first link. The second, regarding the fruit fly study discusses the two in a somewhat shorter article. Both were published in Eurekalert today.

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New species differentiate in far fewer generations than previously thought | 18 comments (16 topical, 2 editorial, 0 hidden)
If so, why can all humans interbreed? (3.66 / 3) (#3)
by maynard on Thu Oct 19, 2000 at 07:45:57 PM EST

If this is true, one might ask why can all humans across the world interbreed? Given that a millennium is about fifty generations, and we've been spreading across the world for long over that, wouldn't you expect that we'd break up into multiple species, unable to interbreed?

YES!

And in fact, this is exactly what's happened with chimps. For example, this article discusses the finding of a new chimp subspecies, making for a total of either four or two subspecies depending on how scientists decide to group the populations. The interesting point here though is that across a far smaller land mass we see speciation in chimp populations, yet we don't for humans!.

I read a while back, but can't find a link in support of, the explanation of this curiosity. It turns out that before we (as a species) migrated from Africa (about 50,000 years ago or so) there was a huge extinction of the human population. About 95% of all human beings died, leaving our genome highly homogeneous. I seem to remember speculation that an asteroid or comet (smaller than the one which killed off the dinosaurs, but the same thing) caused a massive environmental shift which led to the extinction. I believe scientists are looking for evidence to this effect by checking rare elements in stratified land; a geological search essentially. I wish I could find a link in support of this claim... can anyone expound?

Oh well... I just wanted to bring up the obvious counterpoint to this fascinating discovery.

Cheers,
--Maynard

Read The Proxies, a short crime thriller.

Factual error (1.50 / 2) (#4)
by maynard on Thu Oct 19, 2000 at 07:48:01 PM EST

The extinction happened about fifty thousand years ago, we didn't migrate that far back. Sorry. --M

Read The Proxies, a short crime thriller.
[ Parent ]
Almost, but not quite :) (3.50 / 4) (#6)
by Chakotay on Fri Oct 20, 2000 at 07:21:00 AM EST

The reason those species at first don't interbreed anymore is because they're simply not attracted to eachother anymore. They're still genetically compatible, though, and if no mate of their own subspecies can be found they'll go for the next best thing. With humans it's not that much different. Many people simply aren't that attracted to people of a different subspecies. (People who hold to the concept of political correctness might prefer to use "ethnicity" en lieu de "subspecies".) But in humans it's not as strong as in fruit flies, for example.

Basically, those different populations first simply segregate, and choose (if that much can be said) not to interbreed, because they're simply not as attracted to those other kinds as to their own. Sometimes segregation happens, sometimes it doesn't. Fruit flies, salmons and chimpansees apparently segregate, while dogs do not. Cats segregate too. Ferel cats (true ferel cats, not domestic cats that ran away) won't mate with domestic cats, even though they're not even really different subspecies yet.

Humans segregate too, to a certain extent. If we didn't, there'd be many many more mixed relationships. Humans are pack animals, and pack animals would always rather mate with individuals from their own pack than with individuals from another. Our large brain is overpowering our instincts in many ways though. You know, that kind of supports the theory that bigots have brains the size of fruit flies...

Signed by a white male with a black girlfriend... I don't advocate segregation or discrimination - it's just that political correctness gives me a rash.

--
Linux like wigwam. No windows, no gates, Apache inside.

[ Parent ]

Yes, but (2.50 / 2) (#7)
by maynard on Fri Oct 20, 2000 at 09:28:34 AM EST

I may be factually wrong about interbreeding of the various subspecies of chimps... I need to double check that. As a debating point I'll simply hand it over.

But you didn't answer the question... which is why across so many generations, and such disparate land mass, people continue to be able to interbreed. This finding suggests speciation in tens of generations. Now, based on this wouldn't you think that within 100 to 200 generations at least, human populations would differentiate?

Now I REALLY wish I could back my claim up of a mass human extinction fifty or so thousand years back, because I read this but don't have a link for reference.

Your point on sexual segregation and mutual attraction is good, and certainly correct. But I don't think it explains the homogeneity of our genome. Great reply though. BTW: I date a Chinease woman. :-)

Cheers,
--Maynard

Read The Proxies, a short crime thriller.
[ Parent ]

Ah, yes, philosophy! :) (2.25 / 4) (#8)
by Chakotay on Fri Oct 20, 2000 at 10:56:28 AM EST

Why didn't humans diverge? Well, there's a very obvious difference beteween humans and those salmons. In both species, different habitats produced different physical traits, while still maintaining almost the same genome. In case of those salmons, the lake salmons had simply lost the ability to breed in the river at all due to those physical traits. The lake males however are extremely attractive to all females - but the offspring of a river female and a lake male will probably never be able to compete with their rivals in either location.

When humans spread across the continents, they too adapted to their surroundings, but not in such a way that it became impossible to interbreed with other groups either physically or genetically. In fact, many people agree that bastards are the most beautiful people, and there's a very good reason for that: mixing genes with another population is a Good Thing, because it prevents inbreeding, and as everybody knows, inbreeding is a Bad Thing because it produces things like ginger hair.

Another force at work is fear of the unknown, fear of things that are different, which has, for a long time, kept most of mankind from interbreeding with different groups. This ofcourse is more a cultural force than a biologic one, but it's a force anyway. Just a few decades ago a relationship between a white and a black person was an outrage. I would say humans haven't diversified because the ability to interbreed is a good thing.

And actually, there is some sort of such diversification going on among humans. Does anybody notice how there's a very clear division between the "populars" and the "geeks", and how they very rarely interbreed?

--
Linux like wigwam. No windows, no gates, Apache inside.

[ Parent ]

I think you're missing the point (2.00 / 1) (#10)
by maynard on Sun Oct 22, 2000 at 11:52:36 AM EST

I'm not looking at this from a philosophical stance, I'm interested in the evolutionary biological perspective. What would Dawkins or Gould have to say about this question?

Now I brought up the point that a mass human extinction some 50,000 years ago is thought by some scientists to be the explanation for why humans haven't diverged into subspecies unable to interbreed. Such a mass extinction would homogenize the genome by killing off the vast majority of genetic diversity within our species. Unfortunately, I haven't backed this claim up with a link.

Many of the things you wrote in your post are undeniable, but irrelevant to the question at hand. I want to know what genetic influences could have prevented speciation in humans across such a large time span. The fact is that you don't know the answer to this question. Neither do I. Neither do the scientists attempting to resolve the issue. However, I think there IS a resolution to this question, and we'll find it not in philosophical sophistry, but through a hard evaluation of the physical evidence. In this case, an evaluation of how the human genome has changed over time. This question will likely be answered in the next decade or so... I eagerly await the findings.

Cheers,
--Maynard

Read The Proxies, a short crime thriller.
[ Parent ]

The salmon are a special case (3.00 / 1) (#14)
by shook on Mon Oct 23, 2000 at 12:43:51 AM EST

I think the salmon and flies are probably not good representations of "average" cases of speciation. These are probably special cases of how quickly speciation can occur.

I always liked the idea that humans don't vary that much because we use our brains to change our environment. When we move to a cold climate, rather than growing thicker fur, we kill some animals, skin 'em, and use their fur.

[ Parent ]
Right, salmon and fruit flies aren't people (none / 0) (#15)
by maynard on Mon Oct 23, 2000 at 09:00:24 AM EST

Right on salmon and fruit flies not being people. I shouldn't draw conclusions about human speciation based on just two studies of disparate animals so far off the evolutionary tree from humans. Fair point.

I always liked the idea that humans don't vary that much because we use our brains to change our environment. When we move to a cold climate, rather than growing thicker fur, we kill some animals, skin 'em, and use their fur.
It's a nice idea, but I don't think it makes much sense. Why would using tools affect speciation? The presumption that by changing our environment to ease survival in local populations, we would somehow normalize selection pressure across the world's population just doesn't make sense to me. That is, how could local populations gaining the benefit of easier survival in a particular environment, somehow prevent differentiation across the global population? Death before childrearing isn't the only form of selection pressure, as Chakotay pointed out in his previous posts (good posts too!). Sexual selection could cause divergence as well. I think the real question is to ask why our genome is so homogeneous to begin with, in comparison to other nearby species such as chimps. BTW, thanks for your input!

Cheers,
--Maynard

Read The Proxies, a short crime thriller.
[ Parent ]

Why would using tools affect speciation? (none / 0) (#17)
by sigwinch on Wed Oct 25, 2000 at 07:02:12 PM EST

To quote Robert A. Heinlein, "specialization is for insects".  Lower organisms, for the most part, are stuck in one place.  There are exceptions like monarch butterflies, which migrate hundreds of miles each year, but most organisms never get farther than a few hundred meters from their place of birth.  Rivers and canyons effectively block them from travelling, nevermind oceans.  Therefore the selection pressure adapts them to the locale where they live.

Homo sapiens, on the other hand, is intelligent and can build tools.  Shoes, stored food, weapons, and clothing allow humans to travel large distances across land and water.  Mobility alone is good at spreading genes. 

There's also a meta selection factor.  Lower organisms are only selected for survival in their locale.  Perhaps humans are selected to receive useful genes from far away.  If you live in a rain forest, it doesn't help your child much to get a gene for water conservation from a desert visitor (this is oversimplified, but it makes the point).  But your distant, wandering descendents will certainly someday meet a drought and be helped by that gene.  Likewise, a gene for buoyancy doesn't help your desert-dwelling child, but your great-grandkids cannot use boats if they sink.  I think the genes for a generalist body and brain are self-reinforcing:  once you have the brain power, what's the point of being 95% efficient at living along a river when you can be 60% efficient at rivers, plains, sea shores, mountains, and deserts.

Compare the laws of survival to a polynomial equation, and biology to a mathetician.  Some solutions (bacteria) are trivial to find.  Other solutions are harder to find by trial and error, but are nonetheless possible, and in the long view inevitable (bugs, trees).  And some solutions require a higher level of sophistication, such as complex numbers (generalism), but once that level is attained a variety of unusual solutions are available (apes, humans, AIs).


--
I don't want the world, I just want your half.
[ Parent ]

Geeks are less sexually attractive (none / 0) (#13)
by shook on Mon Oct 23, 2000 at 12:26:39 AM EST

Sorry for the flamebait subject, couldn't resist. :-)
I've had a personal hypothesis; I thought I would share it. We are herd animals that have been so extremely successful because of our abilities to group into tribes, nations, etc. in order to get stuff accomplished. People complain a lot on these forums about groupthink and herd mentality. Groupthink brings about a lot of bad stuff (bigotry, genocide) but I think it has been an integral part of our species' survival.
A good member of a powerful tribe will be most likely to get food and rear offspring. So a person who fits into the local social norm will be more sexually attractive. A "popular" person will get more support from the tribe. And thus geeks have a harder time finding mates.

Of course, this is all just the chump opinion of a biology student with no background in sociology. Keep in mind, we humans also have all that other great stuff like culture, morals, and free will, to possibly counteract our instinct.
Question: Will geeks become extinct? Will we mold the current social norm so that perl-coding dotcommers (or cadaver-dissecting biologists) become new ideal mates?

Also, my 2 cents on why humans haven't split into new species: The paper said the first barrier between subspeicies was because of loss of attractiveness between two sides. Someone pointed out that we tend to be more attracted to members of our same race. But we still interbreed. One must remember that humans are very horny animals. Unlike most mammals we don't have certain times when we are "in heat." Both sexes are ready for sex almost constantly.
Also, Someone also mentioned dogs interbreeding more liberally than cats. As most people have noticed, dogs will not hesitate to masturbate on a human's leg (which is very far from the same species). Humans can be similarily horny. Some animals are not very selective in choosing mates. I don't know if masturbation would be a sign of a species being less susceptible to splitting, but it makes sense to me..

Wow, while trying to make a scientific point, I think I just flamed geeks, dogs, and the whole human race :-)

[ Parent ]
Memetic evolution (none / 0) (#18)
by bjrubble on Mon Oct 30, 2000 at 04:59:30 PM EST

There's a pretty big thing in Scientific American this month about memetic evolution, which touches on this. Basically the main writer (forget the name but she has a book) claims that the basis of memetic evolution is imitation, which leads to many of the conclusions you've posited. That is, the biological strategy to tap into memetic evolution is "copy the most successful person around you" and thus conformity and hierarchy are natural byproducts.

<rant>
I was actually really disappointed with the feature. They had sidebars by other writers disputing the main feature, and most of them concentrated on the many aspects of culture and whatnot that can't be reached from "imitation" and claiminged that therefore memetic evolution isn't viable. I felt like everybody was failing to really follow through on the biological metaphor. For example, "having lots of progeny" is *one* successful survival strategy for genes, but is far from the only one. To say that memes can be passed through imitation of alpha individuals may be correct, but to conclude that it is the *only* memetic strategy is to fail entirely to appreciate the power and sophistication of evolution.
</rant>

[ Parent ]
Why humans can interbreed (2.00 / 1) (#9)
by Commienst on Sun Oct 22, 2000 at 02:08:28 AM EST

Animals adapt to their surrondings, eventually evolving to better suit their surrondings and creating subspecies.

Humans do not adapt to their surrondings for the most part. We make our environment adapt to us. That is my opinion at least to why we do not easily evolve, and to me it makes perfect sense.

The Aborginies of Australia have been isolated from the rest of the human race the longest. About 18,000 thousand generations until the first europeans arrived on Australia and they did not branch out into a subspecies.

[ Parent ]

Genocide (4.00 / 3) (#5)
by Will Sargent on Thu Oct 19, 2000 at 10:58:26 PM EST

The ironic thing about the mass extinction of the early human race is that some biologists think that it was self inflicted.

One of the indicators of intelligence and a common theme in all intelligent animals is that they exist in large social groups. The larger the social group, the larger the brain, (disregarding body mass as a percentage). Based on this, it's judged that humans exist "naturally" in groups of roughly 100. This is far larger than chimps or bonomos, which split far before that point.

Apes living on the plains (which is where humans evolved) were a big fat neon "EAT ME" sign to anything with four legs and sharp teeth, which is why human beings had to evolve so fast. But after that point? The only competition was from other tribes.

One group got smart, got organized, and used force of numbers to wipe all the other groups out.
----
I'm pickle. I'm stealing your pregnant.

Only 100? (none / 0) (#11)
by shook on Sun Oct 22, 2000 at 11:50:31 PM EST

What early human race are you talking about? I would think the evidence against humans existing "naturally" in groups of 100 is pretty strong. Maybe a minimum of 100. Most humans I know tend to associate in much larger groups :-) This does sound like interesting stuff? Do you have a link? Or where did you read it? Also, I have read some fairly thought-provoking stuff against humans evolving on plains. (moist stools not suitable for arid climates, tendency for children to climb trees), maybe in light forests instead. But I can't remember where I heard it, and there seemed to be some holes in that argument.

[ Parent ]
Groups of 100 (3.00 / 1) (#12)
by SIGFPE on Mon Oct 23, 2000 at 12:14:24 AM EST

Although humans form groups of many sizes it has been argued that groups of size 100 are 'special'. This is the maximum size of group (according to some authors) in which all interactions are direct. Everyone can know who everyone else is, everyone can track the social standing of everyone else and so on. In larger groups humans tend to manage by forming hierarchies, delegating responsibility and acting through proxies.

I've seen the graph of group size vs. brain size in many books but I can't find one on my shelf when I want it! (It may be in Grooming, Gossip, and the Evolution of Language by Robin Dunbar but I'm not sure.)

I think one could give a pretty good argument that this 100 figure is little better than numerology.
SIGFPE
[ Parent ]
Social Groups (none / 0) (#16)
by Rand Race on Mon Oct 23, 2000 at 12:02:37 PM EST

What about ants, bees, and termites? They exist in huge social groups, much more than 100. If intellegence is a concept adaquately applied to hive insects, this would cast doubt on the assertion that large social groups are an indication of intellegence. This would also seem to imply that herd animals are smarter than the predators who feed on them. Are impalas, who travel in herds of up to several hundred, smarter than lions, whose prides tend to be less than a dozen? Or, more so, the solitary big cats like cheatas and leopards?

I would also take contention with your assertion that we developed on the plains, but that is the accepted dogma. I consider it a far to glibly accepted theory for one that has no primary evidence to support it. I'll just give a nod to Elaine Morgan and her seminal work The Aquatic Ape Hypothesis... one of my favorite scientific heresies. ;)


"Question with boldness even the existence of God; because if there be one, He must approve the homage of Reason rather than that of blindfolded Fear." - Thomas Jefferson
[ Parent ]

New species differentiate in far fewer generations than previously thought | 18 comments (16 topical, 2 editorial, 0 hidden)
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