How many offspring will a maple tree have?

Maple seeds/fruit

The maple seeds/fruit (known to botanists as samaras, and, in some cultures, as whirlybirds or helicopters), are usually abundant. There are a couple of dozen of them in this photo, which is of a small part, maybe 2 or 3 percent or less, of the whole tree.

How many of these would you expect to grow to be mature maple trees? And, more broadly, how many new adult trees would you expect this maple tree to have as offspring, during its life?

The answers to these questions may surprise you. They are none, and one. Why? Here's why. If each and every one of just the seeds in this photo grew to maturity, and other maple seeds did the same, and continued to do so for a few generations, the world would be covered in maple trees. It isn't. Unless there is an expansion of maples, each maple, on average, produces one offspring that reaches maturity and makes another generation's worth of maple seeds. On the other hand, if the replacement rate is less than one new maple per maple tree, it wouldn't take long for maples to vanish.

The usual replacement rate for organisms is one adult descendant in the next generation.

There are exceptions, but they must be temporary. Humans have often produced more than enough to replace themselves, and human populations have expanded. But this can't, and won't, go on forever. Other organisms have also had growing populations. Fire ants in the southeast US come to mind. There didn't used to be any, but now many a pasture has lots of nests visible. And, conversely, other types of living things have disappeared, or have nearly done so, such as cougars, because they don't replace their population numbers.

Darwin's concept of natural selection used the ideas of lots of offspring, and that the fittest survive. Although we can see no important differences between the maple seeds in the photo, it is likely that there are some genetic differences, giving some seeds a better chance than others. (Chance also plays a role -- where the seeds land surely would make a difference in their ability to survive.)

Keep growing and multiplying, but don't take over the earth's surface! Thanks for reading.

Sunspots 508

Things I have recently spotted that may be of interest to someone else:

Computing: Gizmo's Freeware tells us how to configure Adblock Plus (an add-in for major browsers) so that it does a better job of blocking ads.

Relevant warns of some dangers of social media. They aren't all the same ones you've already heard about.

Politics: Michael Gerson, columnist for The Washington Post, does not think President Obama's response to terrorism has been serious enough. But, he says, the President, nor the one before him, should or could have spoken against Muslims in the way that some people think that they should have.

Science:  Wired reports that the Hubble Space Telescope has captured three of Jupiter's moons, moving in front of the planet's surface. Eclipsing, in other words.

Wired also tells us that the hydra, a common, but nearly-microscopic animal, is potentially immortal.

Wired also tells us how it is possible for a baby to have three parents, in the sense that she gets genetic material from all three of them.

Sports: USA Today, ESPN, and many other outlets tell us that Dean Smith, great men's basketball coach, and greater man, has passed away.

Image source (public domain)

Sunspots 489

Things I have recently spotted that may be of interest to someone else:
Christianity: It's not out yet, but here's a blog post warning Christians not to take the Left Behind movie too seriously.
A splendid lecture on how God is seen through nature.
Computing: Be careful of pirated e-books. Apparently, some of them can hack your Amazon account.
Relevant has posted a map showing all the web-connected devices on the planet. Interesting, but perhaps not terribly surprising -- web use is concentrated in a few places.

Science: One of the advantages of being sexual is that the offspring have new and unique combinations of the genes of their parents. But Wired reports on a microscopic organism that takes such recombination much further than any other known living thing.
Wired also reports on a parasitic worm that invades the eyestalks of snails, so it can be eaten. Really. There's a short video.
Image source (public domain)

Response to comment on science in Tolkien and Lewis

On November 11th, I posted a comment on some of the science in the writing of J. R. R. Tolkien and C. S. Lewis. The post was meant to poke gently. As I have indicated, Tolkien and Lewis are two of the writers who have most influenced me, and I honor their achievement. No human writer has created a perfect work.

I did not, but should have, indicated that I was speaking of Lewis's Narnia books, not the space trilogy.

I received three comments, which is a landslide for this blog, and I much appreciate all three. The last commenter, Jeremy Pierce, said, in part:

"Tolkien's world is not flat. It's this world in the distant past."

Sorry, but I stand by my original statement, which idea was not original with me. Tolkien's world was meant to be flat, at least in the earliest times described in the Silmarillion. (Unfortunately, I am on an extended absence from home, and didn't bring that book with me, so I am operating without full documentation here.) As I recall it, the two lights of the ancient world lit the whole earth, which would not have been possible if it had been spherical. Kristine Larsen's long, but excellent, article on the Astronomy of Middle-Earth mentions the flatness toward the end. See also this document, part VB 2. Try a Google search on Middle-Earth flat, and you will find many other references to this.

Pierce also said:

"Many famous dwarves in the lists could have been women for all we know." True, but I believe I am correct that only one was mentioned as being female, and I doubt seriously that any such famous dwarves were meant to be female by Tolkien.

Tolkien isn't the only one to have had mostly, or entirely, male dwarfs (or dwarves). As I pointed out, Lewis also does. So, for that matter, did Snow White. As I recall the tales of King Arthur, by Howard Pyle, there are quite a few dwarves there, too, and all of them were also male (but so were the knights).

Pierce also points out that Sauron had enslaved not only Mordor, but other lands, and that these were supposed to have supplied Mordor (or, as he says, perhaps the supplying was done by evil magic of Sauron). Pierce is correct. However, my point, which was not well made, was that it seemed to me that Tolkien had fictionally amassed such a large army, including some large beings that would have required lots of provender, and in such an isolated place, that provisioning from afar by horse and wagon train, or some such, doesn't really seem realistic.

Why is there sex?

When I taught biology, I could count on an answer to that question, whenever I asked it: "reproduction!"

I then pointed out that many organisms reproduce just fine, thank you, without any sexual activity, and that an awful lot of sexual activity, especially in humans, has little or nothing to do with reproduction.

So why is there sex? Well, I'll give the common biology text answer. (The real one, of course, is "I don't know," or "That's the way God made things," or some such expression of ignorance.) That answer is that sexual processes are a means of combining the genes of two parent organisms, thus allowing better combinations of their genes to appear in their offspring, and be selected for.

Sex is not found in all species of organisms. Where it is found, it often has profound consequences -- consider the fate of the male praying mantis, for example. Regardless, I'm glad it exists, because without it, I wouldn't be here.

Another, related question, that we also can't answer is how Jesus Christ originated. Did he have any genetic material from Mary? Was a Divine sperm created within her womb, by the Holy Spirit, that united with one of her eggs? We don't know.

I have also posted on "Why do living things have cells?"

Thanks for reading.

C. S. Lewis (and Tolkien) and biology

Let me make one thing perfectly clear. I appreciate the writing of C. S. Lewis, and have been deeply influenced by it, I hope. As evidence, I cite my article on the bioethics of C. S. Lewis, which was published in hard copy, and has been posted, by the American Scientific Affiliation, which I appreciate. (They did so without mentioning my affiliation with SWU, because I was on sabbatical at Bryan College when I presented this to the annual meeting of the ASA. I am grateful to both institutions.) Unfortunately, there was an error in scanning the document. "o, n bod % *" should be "own body." As more evidence, I posted, earlier this year, a series on temptations in the Narnia books (see here for last post). I subscribe to, and read, Arevanye's C. S. Lewis blog.

Here's another thing to make clear: If you think reading any criticism of the details in Lewis' books would spoil your future reading of his works, don't read this post any further.

A third clarification: Please remember that this blog is subtitled "musings . . ." That's what this post is.

I found Lewis in the children's section of the University of Wisconsin library, around 1960. Perhaps I should have been studying for my courses, or working on my research, but I'm glad I found the Narnia books. I have read them many times. I look forward with mixed feelings to the forthcoming film based on the series.

Lewis has been criticized, I believe by Tolkien, for one, for not being careful with details. (If anyone out there can put a reference for this in a comment, I'd appreciate it! Thanks in advance.)

Here are some of the details that don't ring true to me.

1) No females. I know, there are females on Mars, in Out of the Silent Planet, and female characters have strong roles to play in Perelandra, That Hideous Strength, and the Narnia books. Till We Have Faces is narrated by the main character, a female. But there are strange gaps. There don't seem to be any female dwarves, or marshwiggles, or earthmen, in the Narnia books.

2) Populations too small. Aslan could, of course, maintain them, no matter how small. But, in Prince Caspian, there seem to be just a handful, or even less, of hags, bears, badgers, werewolves, and others. There are a number of real species of organisms on current real endangered lists, with more than a handful of members. Inbreeding, accidents, and the like take their toll. Species can't be expected to survive with numbers as small as Lewis implied.

3) Food and supplies. Authors often neglect this. I probably would, too. Most fiction works are not about agriculture or commerce. But, for example, how does the giant house, Harfang, heat itself? Lewis describes profligacy in heating it, from wood fuel, but Harfang is in the middle of a "desolate, rocky plain" (The Silver Chair, New York: Macmillan, 1953, p. 78) which is apparently treeless, and Jill, Eustace and Puddleglum spent all morning and part of the afternoon getting to it from where they first saw it, with no suggestion that they went through a forest. There is mention of hunting parties, but none of wood-seeking parties.

Where did Tumnus shop? There is no mention of any market, or even building, in the first part of The Lion, The Witch, and the Wardrobe, save the castle of the witch.

How did Narnia survive the long winter caused by the witch? Such a winter would have cut off almost all agriculture, grazing, etc.

4) Paths under the ocean. The sea-people in The Voyage of the Dawn Treader are described as riding something like sea-horses, which swim. Presumably they do, too. Lucy sees paths at the bottom of the ocean, used by the sea-people. Why would they need paths, or how would they even make them?

Some parallels between Tolkien and Lewis's subcreations:

1) Both of them had some female characters, but both of them seemed to have whole populations with no females. (I'm not including the Ents.) Though Tolkien wrote that it was difficult or impossible for non-dwarves to differentiate the sexes, he mentions only one female dwarf, Dís, Thorin's sister, in the trilogy, The Hobbit, or The Silmarillion, and she was a very minor character. (Besides my memory, see the entry on her in The Encyclopedia of Arda.) I don't recall any evidence of female orcs at all.

2) Both of them created flat worlds.

3) Both of them had an interest in stars. In The Last Battle, Jill Pole is described as being very familiar with the stars as guides. Frodo and Sam saw a star while in Mordor, and this encouraged them. Stars are characters in The Voyage of the Dawn Treader, and Elrond's father became a star, or at least a beacon in the sky, in Tolkien's world.

4) Both of them created worlds that, in many ways, were medieval. Horses, armor, swords and spears and bows and arrows, castles, or at least castle-like buildings, all abound.

5) I really wonder how Mordor, a desert waste, but with vast hordes of various kinds of beings in it, was provisioned.

Crumbolst has posted some insightful commentary on The Lion, the Witch, and the Wardrobe, which sort of considers the same ideas as I am here.

I previously posted on my own article, but thought, as the time for the opening of the movie based on the first book in the Narnia series approaches, that it made sense to do so again. This post is not a duplicate of the former one.

Thanks for reading!

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Added Jan 22, 2008: A subsequent post, responding to a comment on this one, may be found here.