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"If evolution is true, why are there still chimps?"

I once heard PZ reply to this popular creationist question by pointing out that, although many Minnesotans are descended from Norwegians, there are still Norwegians. This isn't really a good analogy, however, because Minnesotans and Norwegians aren't separate species. We know this because they can interbreed, producing healthy children. At the end of this post I suggest a better answer, indirectly inspired by this week's paper.

Two of evolutionary biology's central questions are: how do species change over generations? and how does one species split into two? We have many detailed examples of small evolutionary changes occurring over days (in bacteria) or years (in animals and plants), so one would have to be very close-minded to deny major evolutionary change over millions of years. But major evolutionary change is not enough, by itself, to split one species into two. One subpopulation within a species must change, while the rest of the species either stays the same or changes in different ways. This divergence cannot happen if the two subpopulations continue to interbreed at high rates. In other words, speciation requires some reproductive isolation.

Often, reproductive isolation is a byproduct of geography. After a few individuals (or a pregnant female) cross a mountain range or are blown from the mainland to an island, they no longer interbreed with their ancestral population. Over many generations, random genetic drift or nonrandom natural selection can change the isolated population enough that they can no longer produce healthy offspring with the original population, even if they come back into contact.

Sometimes speciation can occur without a major geographic barrier, but reproductive isolation is still required. This week's paper shows that this has happened and is still happening in Europe.

"A continuum of genetic divergence from sympatric host races to species in the pea aphid complex", by Jean Peccoud and others, was just published online in the Proceedings of the National Academy of Science.
aphid.jpg
Photo by Jean Peccoud

The authors collected 1090 pea aphids feeding on 19 different species of wild and cultivated legume plants across Europe. When they developed a family tree for these aphids, based on their DNA, they found that they fell into 11 distinct groups. The most closely related aphids were those feeding on the same host species, rather than those from the same geographic area.

There were 11 distinct "biotypes", but are these all separate species? In other words, how complete was reproductive isolation? About 9% of aphids were found on the wrong host for their genotype. These "migrants" could, in theory, have mated with individuals there. But was there enough interbreeding to prevent speciation?

To find out, they looked for hybrids, whose DNA showed they resulted from mating between different biotypes. Three of the biotypes are apparently separate species, because no hybrids between them and other biotypes were found. The other 8 biotypes did produce hybrid offspring with other biotypes, at least occasionally. Genetic differences between biotypes were greater, but not much greater, for those identified as separate species.

Given the rarity of hybridization among some of the other biotypes, will some of these also evolve into separate species? This could happen if differences among host plants result in tradeoffs, such that aphids that grow well on one host grow poorly on others. In that case, hybrids may do poorly on either host and there would be strong selection to feed and mate only on the preferred host.

Here's my answer to the creationist question:
"Have you ever had sex with a chimp? No? Neither has anyone else, for a long time. That's why there are still chimps."

Comments

Hold the boat. The myth of 'genetic isolation' between humans and (our second closest ancestor) gorillas, was refuted by esteemed science writer Michael Crichton way back in 1980! I'd like to see you defend your inane liberal ideology in the face of such powerful evidence.

I approved this comment, thinking it would amuse readers, but am starting to suspect this may be a Poe, which Urban dictionary defines as:

"A person who writes a parody of a Fundamentalist that is mistaken for the real thing. Due to Poe's Law, it is almost impossible to tell if a person is a Poe unless they admit to it."

How about it, Will? Knowing that gorillas are our second-closest relatives didn't quite seem to go with calling Crichton "esteemed."

One thing evolution cannot explain: the pride in felines.

All felines.

From the alley cat to the lion.

Neither adaptation, natural selection, nor instinct can explain this unmistakable exclusive trait of the feline.

Maybe if we could stop obsessing on monkeys and get down to attempting (however humbling it may be) to exploring separate and distinct personality traits of species that have never crossed over and never will, we might discover we've missed a big part of the puzzle. When we stop trying to make a similar piece fit, and have patience until we find the right piece that does, maybe we'll be on to something.

It's one thing to investigate something, it's another to call that investigation a fact. Until then it's just a belief.

Which brings us back to pride. It is truly fitting and right for the feline, but obnoxious and unjustified in the human being. It also gets in the way with science, truth, and facts.

How can we come to a correct conclusion when we are only exploring one side? We cannot. Except perhaps sometimes by chance. But that is not really science which negates the whole purpose of science.

We need to dig a little (okay, a lot) deeper, swallow our pride and investigate it ALL, and maybe we will truly have something. This goes for creationists and evolutionists.

But leave the pride for the felines, they own it.

Thanks for providing this site.

Another Poe?

Can there actually be someone out there who thinks "a pride of lions" refers to their attitude? Or who doesn't know that lions are the ONLY felines that live in this sort of social group (adult females usually sisters unrelated to the adult males)? You don't need to dig any deeper than Wikipedia, if you somehow missed this stuff in third grade.

If all felines DID form prides, the simplest evolutionary explanation would be inheritance from their common ancestor. Living in prides does apparently have a genetic (as opposed to strictly ecological or cultural) basis, which must have evolved after the ancestors of lions stopped interbreeding with the ancestors of leopards, between 1 and 1.25 million years ago. This is still from Wikipedia (citing scientific papers based on DNA analysis of family trees, etc.), but probably beyond what was included in your third-grade science class.

So why did lions evolve group living, when other cats didn't? To answer that question, we really do have to dig deeper. I'll watch for recent research on this, but here's one example: "Evolution of the mane and group-living in the lion (Panthera leo): a review". Journal of Zoology 263 (4): 329–342.

I didn't actually mention monkeys. Chimps and gorillas are much more closely related to humans than to monkeys (i.e., they share a more-recent ancestor with humans than they do with monkeys). Lacking tails was one early clue, but now we have DNA-based evidence as well. Orangutans aren't monkeys either, something you might want to remember if you ever visit the library.

I agree that scientific conclusions are always tentative, subject to revision if conflicting data turn up.

One has to wonder what the commenter would think of a murder of crows.

i think monique is referring to cats being somehow "proud". This is humans assigning a human trait to animals.

It sounds like a christian call for us to be "humble" and not think deeply about the world and ignore anything that doesnt conveniently fit into their worldview.

Ok, ok. I admit to being a Poe, damn it. But only to distinguish myself from the above feline-lover. Unless of course she turns out to be a Poe too. If that's the case, I shall doff my hat thee madame, for thy skills vastly exceed mine.

In all truthfulness, I had two family dinners with Michael Crichton when I was about 10 years old. He was in Mendocino, CA, visiting mutual friends. You know what I remember? He wasn't very nice to me. I'd just read Jurassic Park, loved it, and wanted to talk about it with him, but he wasn't having any of that.

Unbelievable. I think I just solved the mystery. His inordinate amount of PRIDE suggests that, instead of intentionally distorting science to sell books and become even richer, he was some sort of highly-evolved feline sent back in time. Now, I'm not sure about this part, but I think his mission was to thwart human efforts to curtail global warming so that the lions of the future can invade Europe.

Who knows what kind of feline plot Bill O'Reilly is perpetrating?

Dave: excellent!

Allan: you are probably right, but she seems to accuse scientists of a particular kind of pride, namely, thinking we already have all the answers, whereas the reason we do experiments is to find out things we don't know. Cats aren't too proud to eat garbage or have sex in public, but do they think they know it all, like some religious zealots? Or are they curious to learn new things, like scientists?

Will: reminds me of a story where someone tricked the new CEO of a car company into believing the previous CEO had been a space alien bent on modifying earth's climate to prepare for their invasion.

Guys, guys, guys! All these poes are not helping! The oft-cited Fundamentalist question: "Why are there still chimps?" is a straw-man fallacy - commonly presented by Evolutionists to show how ill-informed Fundamentalists are about the process of Evolution. The result is: 'See how stupid and dumb the Creationists are? Hee, hee, hee! What a bunch of morons! Let's all have a big laugh now so we can smugly ignore their other exasperatingly difficult real critiques of Evolution.'
The headache is that there are a great many complexities at the molecular level with the process of Evolution - most of which we don't really understand. Giving names to processes ("Macro-evolution" / "micro-evolution") doesn't help, either! Heads-Up, Biology Teachers: Giving a name to something doesn't mean you understand the process.
It would help everyone if we stopped asking (and repeating) the misunderstandings of both sides and honestly considered the evidence that is available - not agreeing simply because it suits our theological or atheistic paradigmatic aesthetics.

So many people worry about where they came from, yet no one worries about where we're headed. EVOLVE!

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