Chapter 2
Speciation
Selection favors early speciation in turn limiting gene pool size.
Last chapter explained that inbreeding does not do its harm by the effect of genes. You got that, right? The smaller population is able to purge itself, whether by genetic drift or selection against deleterious genes than the larger population. Were the opposite the case, it would be no great problem. We could breed with strangers with wild abandon. But inbreeding IS a problem. The head of the Florida Cracker Horse Association once said: Inbreeding is line breeding that goes badly; line breeding is inbreeding that goes well. Inbreeding hangs over the heads of these horse lovers (Don’t get me started on how much I love the gentle Crackers and their swift, tireless horses.) It is not genes. We have proved that. It is Something Else, and it is inherited but it is not genes. And that Something Else is the mechanism that we urgently need to understand.
Consider an animal and a niche.
A Imagine a niche here
An animal and a niche.
Fig. 8
The animal is “A.” The niche, sort of like a crude house that did not come over on Dreamweaver, provides the animal with food, shelter, air, water and whatever else it needs to survive and reproduce. This is not an individual animal but a population that mate at random with each other but not outside and carry on generation after generation. There will be variation within the population – mutations and so forth. The variant may nudge the animal toward the niche or in some other direction. It is inefficient, but over time the animal population is pushed toward the niche. This is called selection.
A Imagine the niche and an arrow drawn to show A pulled toward niche.
An animal drawn toward a niche by selection.
Fig. 9
Now the animal is in the niche; imagine the animal in a little house. . Any variation is tested against how well it lets the animal do in the niche. This is now more efficient. The animal is unlikely to be dislodged from its niche by an outsider, B.
B
A This is in the little house, but B is not
The animal in the niche has an advantage in keeping the niche against another animal not perfected for the niche.
Fig. 10
Now suppose there is a new niche, and there are two animals, either of which might be able to change in a way that permits it to exploit the new niche.
A B
Imagine a couple little drawings of houses.
A new niche that might serve descendants of either of two animals.
Fig. 11
The first that gets there has the advantage. So, SELECTION IS A RACE.
While the two animals are competing to reach the niche first, one may divide itself into two species. This is called speciation. Here the new species is A’. Arrow indicating one species becoming two.
A’
A B
Two animals drawn toward a niche, but only one has undergone speciation.
Fig. 12
Now the A animal can compete for the new niche while the A’ animal stays in the old niche. In fact, the A may get a bit of a boost because, its old niche being filled, it is not held back as much by selection in that direction, while B animal is drawn in the direction of the new niche as well as the one it already occupied. So, SPECIATION IS A RACE. Of course, the animal does not knowingly exert itself in this race. Being around animals one notices them engaged in goal oriented, purposeful, conscious, strenuous behavior. But in this race, there is no conscious strategy.
I am not aware of any general consensus regarding how long speciation takes. It can happen very fast, for instance if there has been hybridization, the combination of two species. In fact, recent work1 has found evidence that a hardy large cactus finch male was blown over 60 miles to an island where there were no such birds. It found a mate among the resident medium ground finches, and they raised a brood of hybrids. These proved fertile and almost all chose mates from the same line. Thus, they were separated from the paternal line by distance and the maternal by choice. It was a new species, so far only called Big Bird. It turns out that such instant species are not all that rare although quite rare in mammals, and a condition called introgression in which a snippet of chromosome from one species turns up in a different species is not rare at all. Presumably it began as some sort of hybridization.
When I look at reports on the topic, I fail to notice mention of pre-zygotic and post-zygotic infertility. The principles are fundamental but not so trendy. Far less do I see mention of an epigenetic process, such as we will examine later.
Bar hybridization, I take two thousand generations as plausible time to speciation. That’s only a guess, and you can take any number you like, but don’t go overboard and say two million or we shall have words. And do not hem and haw that two thousand generations seems too short a time for the necessary genetic mutations to occur.
Let me tell you a story I heard at Harvard Med. I am sorry I cannot give a reference, and I doubt it was new with my raconteur.
A woman set up a boarding house for working ladies. She decided that the models were so pretty they would have a lot of gentleman callers, so she put them on the first floor. Telephone operators would have a lot of social contacts, so they went on the second floor while the school teachers went on the top floor. She noticed that the models didn’t have many gentleman callers, so she got out her stethoscope, and when a gentleman was calling on one of the models she listened at the door and heard, “Oh, you’re crushing my corsage … oh, you’re smudging my makeup … oh, it’s eight thirty, time for my beauty sleep. Get out.” Next time, she listened at the door of one of the telephone operators. “Your three minutes are up, please.” And all night every night there was the clomp of gentleman going up to the top floor, so she listened. “OK, we’re going to do this again and again until we get it right.”
We are not looking at genes. Go back to the first chapter and read it again and again until you get it right.
Imagine a niche in a valley:
A
A
A
A valley offering a wide expanse for animal A. Imagine a sketch of a valley.
Fig. 13
A kind of animal roams the valley and finds it an adequate niche. Caution: we have used letters to mean populations and arrows to mean development, but now letters will be individuals and lines will be suggesting the valley.
Now consider two individual animals in the population that are siblings, as closely related as they can be, A and A.
A, A
Siblings in the sketch of the valley.
Fig. 14
One yields to wanderlust and goes across to the far side of the valley.
A (Valley goes here.) A
The siblings are geographically separated.
Fig. 15
Then it gets cold, and a glacier forms, splitting the valley. The animals cannot cross the glacier.
A G A
G = glacier
The siblings are now separated by the environment as well as by distance.
Fig. 16
Two thousand generations pass. In that time speciation has developed. The descendants are A and A’, which are now different species. If the glacier melts, they cannot mate and have fertile offspring.
A, A’ Indicate that his couple is infertile
Fig. 17
Now suppose instead of a glacier it gets warm.
A, A, A, A, A, A A, A, A, A, A, A, A, A, A, A
A, A, A, A, A, A, A, A, A
A, A, A, A, A, A, A, A, A
The population has grown. There are lots of members on both sides of the valley.
Fig. 18
The population rises to well over a thousand. Descendants of a single A can get to each other, but that is not likely to happen right away. As you know in humans there are 46 chromosomes, parts of the cell involved in many things and eventually speciation, of which 22 pairs are autosomes, structurally the same if different in detail. For a chromosome from A to wind up in the same animal as another of the same specific chromosome from A will take on average something like 2,000 generations. By then the descendants are A and A,’ which are different species. They cannot have fertile offspring. Since this is true of every member of the population, the whole population dies out.
That is what you get if you restrict your thinking so that only genes are inherited. Since it is obvious that there are any number of species with more than a thousand members, something else must be at work. That thing is the mechanism we are looking for. Something must be stabilizing populations so they have robust resistance either to rising toward a thousand or falling toward zero as of course one would expect if the members of the population did change in the face of changes in the environment or in their own makeup.
We have very few clues so far:
There is something that stabilizes population size. It is inherited. It is not a matter of genes.
There are going to be more clues. When I first began work on this, the word “epigenetic” had not been coined. It was all DNA sequences.
So much for the critical facts. Selection is a race. Speciation is a race. Thus, speciation cannot be indefinitely postponed. Rapid speciation limits the size of a random mating population that can be sustained.
Now let me expand a bit. As before, this part will not be on the hypothetical quiz. If you find it of interest, well and good. If not, do feel free to skim or skip.
Many years ago, in the flush of new knowledge we shall examine later, I thought I needed but spread the word and a tidal wave of enthusiasm would sweep the world of science. Brilliant minds would turn their incandescence to the issue. Students would curse me for having made their lives that much more miserable. Busybodies would whisper to each other that so and so should not marry this and that because they were simply not kin.
There was to be a big genetics conference in Sidney, Australia. The minds I needed to illuminate would be there. I made arrangements to go to this antipode, and then terror struck. My inner machinery told me that I was attempting more than was mortally possible. It was hopeless. I countered that my approach was invincible. Then why was I so scared?
I would need a friend. I would need someone to keep my spine straight, my eyes ablaze and my voice firm. Since I was unmarried, it would have to be a casual female acquaintance. There was a renaissance festival in my town, Largo. I had attended it for years, hoping the fates would lead me to some suitable bride. I think the fates did their part, but the other side of the bargain never seemed to come close to going through. Still, I knew a raft of really good-looking young women, so it should have been easy.
I approached a fellow cast member and asked her whether she would like to visit Australia. She said it was a tempting offer, and she would give it her full consideration. Time passed. I began to feel a bit uneasy. If she did not accept, it was getting close to the time when another would be unable to make arrangements. So, I offered the trip to another young woman with the understanding that there might be two of them. Time raced. This one would not say yay or nay either, so of course I asked a third. She agreed to come but said she had to renew her passport. The ladies managed to keep me so frustrated that I didn’t stay scared.
In the event, as a friend began driving us all to the airport, the mailman showed up with the passport. So, I began the adventure accompanied by what I reckoned were the three prettiest women in the county.
When we went to sign into the convention, the clerk said one of them did not have a student card and couldn’t enter. Somehow, between my money, the fact that we had gone half way around the world and the fact that he was in danger of disappointing more pulchritude than had even surrounded him in his life, we got in.
What I had was a poster presentation. Styles vary. The deal was that you could attend your poster certain hours and at some point, an authority would come by and look at it. The ladies certainly did their part, dragging scientists from all over the hall to come look at my evidence. The scientists took an interest in the women but precious little in the evidence.
Eventually the moment came when the big shot dropped by, unannounced as it turned out. He was a little guy. He looked at my evidence and said, “But you don’t have a mechanism.” So, the bonnie blue eyed, what? As a big shot, I thought it would be up to him to account for my evidence. My statistics brooked no argument. I had vaguely heard of epigenetic something or other, and surely if it was a possibility, he knew about it. But he spoke as if my lack of mechanism ended it, turned on his heel and walked away from the greatest puzzle and biggest opportunity of a lifetime.
I certainly had my work cut out for me.
Do not think that I was the first to realize that speciation was a race. Alfred Russel Wallace had realized as much. He was a naturalist who spent an enormous amount of time and energy studying wild populations. He developed the theory of speciation by natural selection and wrote Charles Darwin and asked him what he thought. Darwin had spent an enormous amount of time studying captive pigeons. If ever you want to be famous, read Darwin’s book, The Origin of Species or How Europeans are Destined to Drive Lesser Races to Extinction. It’s all about pigeons. Reconcile Darwin’s remarks with the laws of Mendelian inheritance or epigenetics. I have tried and cannot.
Anyway, Russel wrote Darwin. Darwin showed the letter to friends. They said Darwin had the money – there was a connection with the Wedgewood china folk – and he should write a book up and print it right away. He did, so it is Darwin’s theory of evolution, not Wallace’s.
In the book, if memory serves, Darwin lavished one entire, if rather brief, sentence on his subject. “As for speciation, it is happenstance because hybrid infertility never did any species any good.” If you can’t blow that one away, go to the beginning of the chapter and read it again and again until ….
But Wallace understood. He pointed out that once a new niche is entered, strong selective pressure favors speciation so as to be able to monopolize the new niche and keep the old.
Alas for science, this brilliant man did not lose his knack for getting hoodwinked. He fell among spiritualists and, far from his field of comfort, swallowed their fraud sinker, hook and line. To be frank, there is more to the for-me-inherently-marginally-dishonest practice of the work of a medium. You see, in effect she or he is a counselor and a lot cheaper than a licensed councilor. There are also some cosmic issues that suggest we ought not be too smug about science. But I am talking here about science, and dismiss alternatives.