In this post, we will do the following:

• Discuss historical and contextual aspects of the term “Natural Selection” in order to make clear exactly what it might mean (and not mean).
• Provide what I feel is the best exact set of terms to use for these “three conditions,” because the words one uses are very important (there are probably some wrong ways to do it one would like to avoid).
• Discuss why the terms should be put in a certain order (for pedagogical reasons, mainly) and how they relate and don’t related to each other.

When you are done reading this post you should be able to:

• Make erudite and opaque comments to creationists that will get you points with your web friends.
• Write really tricky Multiple Choice Exam Questions if you are a teacher.
• Evolve more efficiently towards your ultimate goal because you will be more in control of the Random Evolutionary Process (only kidding on this third one…)

Here are some definitions of Natural Selection I found on the web for your review:

• The differential survival and reproduction of organisms with genetic characteristics that enable them to better utilize environmental resources [source]
• Natural selection is the process in which some organisms live and reproduce and others die before reproducing. Some life forms survive and reproduce because they are better suited to environmental pressures, ensuring that their genes are perpetuated in the gene pool. [source]
• Process by which the genotypes in a population that are best adapted to the environment increase in frequency relative to less well-adapted genotypes over a number of generations. source
• The concept developed by Charles Darwin that genes which produce characteristics that are more favorable in a particular environment will be more abundant in the next generation. [source]
• the differential survival and/or reproduction of individuals within a population based on hereditary characteristics. [source]
• The process by which new species evolve when influenced by selective pressure (Martin et al, 2000). Natural selection occurs when the natural factors of environmental resistance tend to eliminate those members of a population that are least well adapted to cope and thus, in effect, select those best adapted for survival and reproduction (Nebel et al, 1998). [source]
• central thesis of the biologist Charles Darwin which suggests that within every population of living organisms there are random variations which have different survival value. Those which aid survival (or enhance reproductive capacity) are ‘selected’ by being genetically transmitted to succeeding generations. [source]

There are things I don’t like about most of these definitions. A definition may focus on environmental conditions and thus ignore many very important other things such as developmental processes and mating. Definitions may focus on the individual’s survival, etc., which works, but we may want to speak of traits as well as individuals. Some definitions use active verbs such as “ensuring that their genes are perpetuated in the gene pool.” This may not be linguistically wrong but it incorporates teleological concepts, which don’t need our help in creeping into our thinking (especially in the formal definition of a natural force!). There is often a direct link to Charles Darwin. This is good because it is true that this is his concept. However, a modern definition of Natural Selection needs to be Neo-Darwinian. So specifically referring in the definition to Darwin without more attention to the historical development is inadequate. Referring to Darwin’s concept as a concept about genes is jarringly wrong.

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As a whole these definitions are not terrible, but they are mostly flawed for one reason or another. The definition I want to lay out here will have specific reference to the same process these definitions are about. However, there is also one very large problem with many of these definitions that is a bit more subtle than most but that is, to me, critical, that relates to the object of study. It is probably best to not assume a one-to-one correspondence between the process of Natural Selection that we are going to describe here and the concept of “adaptation.” Ultimately, I would like to say that “adaptation” is the noun and “Natural Selection” is the verb in a key evolutionary process. But having said that, a useful and precise definition of Natural Selection may have to leave out processes that are nonetheless related to adaptations, both in terms of understanding the historical aspects of an adaptation and the functional aspects, but that do not fall under the process “Natural Selection” as it is best defined.

An adaptation may reach its particular form through the process of Natural Selection, but there are aspects to that form that have to do with, for instance, abiotic realities. You cannot have adaptations that involve swimming without bodies of water, for example. Our definition does not say “Oh, and there must be air, and water, and trees to climb in.”

I actually want to provide TWO different (linguistically) but identical (functional) definitions of natural selection. The first is the coolest one, the simplest one, the one that makes you think. The second is a better pedagogical tool and serves better as the basis for adaptationist analysis of biological systems. The second also links better to certain historical aspects of the development of the concept.

The first definition is conceptually related to the following definition of evolution:

Change in allele frequency over time.

Which is something of an oversimplification, but an allowable one. And in this context we can define Natural Selection as:

Nonrandom elimination of alleles.

I believe that this was suggested by Ernst Mayr.

This is a cool definition because it is short, sweet, and correct. Note the very important asymmetry that this definition implies. There is no non-random generation of novel alleles. Only elimination. This jibes with selection as a creative force, but neutral processes as providing the raw material. Neutral processes lay down the sediments that become the marble, Natural Selection is the sculptor. The adaptation is the sculpture.

The second definition, and the one I really want to get to, involves the so called “three necessary and sufficient conditions” and it goes something like this:

1. Variation in a trait
2. Heritability of the trait
3. Differential fitness conferred by the trait.

Just as important as these elements is the theoretical and logical framework in which they are placed. They are the THREE NECESSARY and SUFFICIENT conditions. Let’s parse that out more.

Three … That there are three is obviously because all important things happen in threes, sevens, or tens, for unknown cosmic reasons. Be that as it may, I want to point out that “three” implies “three different” things. If two of them could have been combined, then we would have only two. But there are three.

What this implies is the following: If there is a trait that varies, then it meets the first criterion. But “No,” you say, “what about hair color? If I see a bunch of people with different color hair, and I KNOW they dyed their hair to get that way, this is not trait related to selection. So it does not meet the first criterion.”

But you would be wrong. Remember, there are THREE DIFFERENT criteria. The first one is variation. If you see a bunch of dogs and they have different coats because they went to a very creative groomer, or a bunch of students standing around the cafeteria with blue, red, unnaturally black, and vivid yellow hair because they all went to Target and got dye and colored their hair, then in both cases you have met the first criterion because there is variation. By saying “these traits are not inherited” you have skipped ahead and cheated.

The second criterion is usually stated as “heritability” and that is a small problem, because the term “heritability” has a specific meaning in biostats that falls apart for our present use. It is the measured variance in the genotype divided by the measured variance in the phenotype, squared. (Thus indicating something like the proportion of measured phenotypic variance that is accountable by genetic variation.) What is meant in our definition, however, is this: Is the variation in the trait conferred by genes? The dyed hair and the clipped poodle do not meat this criterion.

The third criterion is often stated as “Differential Reproductive Success” and that is simply wrong. The correct term is “Differential fitness” and it has to be differential fitness that is conferred by the trait. Why fitness instead of Reproductive Success (RS)? That is an important matter, and I will not discuss it here. For now, let’s just go with it.

OK, back to the theoretical context: Necessary.

Why are these three necessary? By necessary it is meant that ALL of them have to be true or it is not Natural Selection. This is fairly obvious. If you are missing any one of these three then what you are observing may be an interesting phenomenon but it is not Natural Selection. This also speaks to the need to be Neo-Darwinian. Darwin was aware of inheritance, but lacking an understanding of the mechanism, the necessary requirement of “heritability” (remember, shorthand for “the trait is passed on by genes”), any Darwinian definition (and I’ve avoided using his specific words here) is not good enough.

I had said at the beginning that the ordering of the three conditions is important. This is because they interact with each other in order. Here is how.

First, you need a trait that shows variation. Second you need to show that that trait is heritable, AND that the inheritance pattern relates to that variation. Third you need to show that the variation that is heritable maps on to differential fitness. So there is a strong logic to the order, that is embedded in the functional meaning of Natural Selection and any test criteria that are set up to investigate possible cases of it.

So the ordering works both for the understanding of the concept (pedagogy) and the investigation of the phenomenon.

Sufficient. That is a really important part of the context for this definition. If these three conditions are true, then Natural Selection IS happening. There is no alternative. The force of Natural Selection is activated when these three conditions are met, no matter what.

Does this mean that the selective force will have an effect? It depends. Natural Selection is a force, but there are other forces, including other instances of Natural Selection that may be operative in a particular organism. Gravity is a force but a fly can still walk on the ceiling. The gravity is still acting on the fly, but so is another force (adhesion) that keeps it up there.

This is an important point that bears emphasis. When the Three N&S Conditions of N.S. are working, Natural Selection happens. Period. The absence of an EFFECT is due to countervailing forces (including chance, because within it’s operation there are still stochastic effect).

I believe it is incorrect and counterproductive to make “Sexual Selection” distinct from and parallel to “Natural Selection.” Darwin was puzzled by apparent inconsistencies, especially along the lines of exaggerated traits mostly in males, and came up with Sexual Selection as a process to explain this. Fine. But I think it is best to think of both Sexual and Artificial Selection as subsets of Natural Selection.

The term “Selection” by itself is often used interchangeably with “Darwinian Selection,” but often (usually?) as not really meaning the same thing as Natural Selection. Natural Selection works between generations on reproducing organisms and their genomes. Darwinian Selection, or selection in general can work on other things, like prospective students trying to get into law school, or neurons during culling, etc.

This has been an enhanced repost from a very long time ago. You might imagine that I’m about to write a post on Falsehoods related to Natural Selection, and needed this post nearby. You’d be right!

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Other posts of interest:

• How to get rid of spiders in your house
• Why is your poop green?
• How many cells are there in the human body?
• Is there really a plot hole in Harry Potter Goblet of Fire?
• How long is a human generation?
• Is blog ever really blue?
• How to not get caught plagiarizing
• The origin of the domestic chicken
• What are the three necessary and sufficient conditions of Natural Selection?
• How do I get rid of foot fungus?
• Which is better, Tap Water or Bottled Water?
• Has Global Warming stopped?

Also of interest: In Search of Sungudogo: A novel of adventure and mystery, which is also an alternative history of the Skeptics Movement.

And now there is a new book, One Iguana, Two Iguanas: A Story of Accident, Natural Selection, and Evolution by Sneed B. Collard, exploring this story, for kids.

Collard’s book does the science very well. Note, common wisdom is that the two iguana species split over 8 million years ago. Collard says closer to five. There is a more recent study that says closer to five,so I assume this is the one being referenced, but you know how these DNA phylogeny studies are. “You don’t like this date we give you? Wait a few months, we’ll have a different one!” No matter, it is said in this wonderful children’s science book that the two iguanas arose from the Ctenosaura iguanas, and then split on the Galapagos after arriving there, and that is almost certainly correct.

One Iguana, Two Iguanas is a fast read, very well illustrated. It is for kids age 8-12, but you can read it to a younger science oriented geek-child, and if you are an adult who is not a biologist, there is a good chance you’ll get something out of it yourself.

The book is well illustrated, makes a good story, and I’d suggest this time of year, it would make a great holiday gift.

The author has written approximately one gazillion children’s books, and has been awarded several awards.

The publisher, Tilbury House, has a number of great kids science books, including these two I just reviewed.

Start with this paragraph:

But for modern medical science, a baby’s sex would remain unknown until birth. But many mothers today know long beforehand whether a baby will be male or female. Routine ultrasound scans reveal fetal genitals a third of the way through pregnancy, and genetic tests identify sex even earlier. Yet basic questions remain. Is a baby’s sex like coin tossing, or can the male:female ratio be skewed? If sex bias occurs, does it happen through sperm sorting before fertilization or mortality differences in the womb after conception?

Then, CLICK HERE to read the rest of the story, by Robert Martin, expert on such things.

Anyway, recent research suggests, controversially, that the early birds were not built to do this, and may have been too heavy.

Here’s the basis of this suggestion. Early birds had a pelvis that was fused, and thus, limited the size of the egg that could be produced. A smaller egg, with its thinner shell, would have been too weak to allow a bird large enough to produce that egg to sit on it without breaking it.

(There are no pertinent actual fossil eggs at this time.)

The controversy arises from the belief among dinosaur-ologists that some non bird dinosaurs were brooding their eggs at this time, so naturally, birds could have done this. However, if you think about it, maybe that assumption would not have emerged to begin with if this bird study was done fifty years earlier.

Here is the abstract:

Numerous new fossils have driven an interest in reproduction of early birds but direct evidence remains elusive. No Mesozoic avian eggs can be unambiguously assigned to a species, which hampers our understanding of the evolution of contact incubation, which is a defining feature of extant birds. Compared to living species eggs of Mesozoic birds are relatively small, but whether the eggs of Mesozoic birds could actually have borne the weight of a breeding adult has not yet been investigated. We estimated maximal egg breadth for a range of Mesozoic avian taxa from the width of the pelvic canal defined by the pubic symphysis. Known elongation ratios of Mesozoic bird eggs allowed us to predict egg mass and hence the load mass an egg could endure before cracking. These values were compared to the predicted body masses of the adult birds based on skeletal remains. Based on 21 fossil species, we show that for non?ornithothoracine birds body mass was 130% of the load mass of the eggs. For Enantiornithes body mass and egg load mass were comparable to extant birds, but some early Cretaceous ornithuromorphs were 110% heavier than their eggs could support. Our indirect approach provides the best evidence yet that early birds could not have sat on their eggs without running the risk of causing damage. We suggest that contact incubation evolved comparatively late in birds.

Deeming, D.C. G. Mayer. 2018. Pelvis morphology suggests that early Mesozoic birds were too heavy to contact incubate their eggs. Journal of Evolutionary Biology. 27 Feb 2018

One of Darwin’s major contributions to the panoply of theoretical and observational work we call “evolution” was to recognize, describe, and model sexual selection.

Key to Darwin’s original conception is the presence of an aesthetic sense in females that drives male trait evolution to produce elaborated traits. We now have a much more sophisticated understanding of sexual selection than Darwin had. Females don’t merely have this rather Victorian aesthetic. They are, in some species, picking mates on the basis of meaningful qualities and forcing the opposite sex to compete with each other to demonstrate these qualities. We also, today, understand that while it is more often females driving male trait evolution, the opposite can occur, and we even think we know why a particular directionality of sexual selection driven evolution would occur.

Another thing that has been learned over time is the modalities of selection. The early, obvious cases, such as the peacock displaying to the peahen, are visual and use color. Over time we’ve come to understand many other kinds of traits including auditory and olfactory, much better.

A Taste for the Beautiful: The Evolution of Attraction by biologist Michael J. Ryan is an excellent exposition of, and wide ranging sampling of, sexual selection in animals. Ryan ranges across a wide range of sensory modalities. Sexual selection involves direct competition (often seen as fighting) as well as attraction, but Ryan’s book focuses on the latter, on the interplay between Darwin’s presumed aesthetic (but understood as we know of it today) and visual, auditory, olfactory, and other cues embodied in elaborated traits and behaviors.

Since the visual modality is important, it s nice to see ht e publishers spring for a bunch of color plates in the middle of the volume. (This is not a surprise, Princeton makes the best looking books.) Notes are fairly extensive and there is a good bibliography, and it is well written. A very nice book all along.

A Taste for the Beautiful: The Evolution of Attraction could be an accompanying volume in an intro or mid level college course on evolutionary biology. Or, the high school or college biology teacher can simply steal numerous examples from the text. That is what I intend to do next opportunity. But it is really an excellent book for the average science geek such as yourself.

From the editors:

From one of the world’s leading authorities on animal behavior, the astonishing story of how the female brain drives the evolution of beauty in animals and humans

Darwin developed the theory of sexual selection to explain why the animal world abounds in stunning beauty, from the brilliant colors of butterflies and fishes to the songs of birds and frogs. He argued that animals have “a taste for the beautiful” that drives their potential mates to evolve features that make them more sexually attractive and reproductively successful. But if Darwin explained why sexual beauty evolved in animals, he struggled to understand how. In A Taste for the Beautiful, Michael Ryan, one of the world’s leading authorities on animal behavior, tells the remarkable story of how he and other scientists have taken up where Darwin left off and transformed our understanding of sexual selection, shedding new light on human behavior in the process.

Drawing on cutting-edge work in neuroscience and evolutionary biology, as well as his own important studies of the tiny Túngara frog deep in the jungles of Panama, Ryan explores the key questions: Why do animals perceive certain traits as beautiful and others not? Do animals have an inherent sexual aesthetic and, if so, where is it rooted? Ryan argues that the answers to these questions lie in the brain?particularly of females, who act as biological puppeteers, spurring the development of beautiful traits in males. This theory of how sexual beauty evolves explains its astonishing diversity and provides new insights about the degree to which our own perception of beauty resembles that of other animals.

A Taste for the Beautiful: The Evolution of Attraction is vividly written and filled with fascinating stories, A Taste for the Beautiful will change how you think about beauty and attraction.

Michael J. Ryan is the Clark Hubbs Regents Professor in Zoology at the University of Texas and a Senior Research Associate at the Smithsonian Tropical Research Institute in Panama. He is a leading researcher in the fields of sexual selection, mate choice, and animal communication. He lives in Austin, Texas.

Hey, this book has a trailer!

Quotes by Charles Darwin are not just the stuff of memes. Even the fake quotes. They can be the center of long arguments, or at least, they can significantly augment the arguments. For example, did you know that while Darwin never used the term “missing link” he did talk about missing links quite a bit, missing links are central to his thinking about evolution, and all those writers of today who claim that we must never speak of missing links are misguided?

My point being, Darwin quotes aren’t just quotes. They are piece of data related to the development of thought about evolution. There are about 300 pages of just quotes, organized by topic, a timeline of Darwin’s life (just a few pages), and an index. Not all the quotes are by Darwin, some are by others responding to him. Many of the quotes are from letter, labeled, of course, as to whom the letter was writtng.

I happen to have the hardcover version. It is a nicely bound, smallish format binding, a bit like a bible in size and shape. Of course. But since the book is about quotes, and this is sometimes something you might want to look up, one might seriously consider the Kindle version which would allow text searches, to the not very evolved extent Kindle devices let you do that.

In case you did not know, Janet Browne is a top Darwin biographer, an historian of science, currently at Harvard but hailing from Great Britain. She has written extensively on Darwin’s correspondence and other writings.

Years ago, I realize that most of Darwin’s arguments, in On the Origin of Species, are underlain by evidence Darwin would have observed prior to setting foot on the Galapagos Islands. This includes fossil evidence from mainland South America, bio-geography in that region and on the Falklands, other observations, and material in the literature, some of which he was carrying with him.

It is not that the Galapagos didn’t matter. They mattered a great deal, as a natural laboratory of evolution. And it is not clear to what degree Darwin had realized his own theory before, during, and after his Galapagos visit. But, reading whichever version of The Voyage of the Beagle you like, that Darwin’s post hoc reconstruction of the ontogeny of his own reasoning starts out long before the Beagle closed in on Valparaiso, on the Pacific Coast.

Origins of Darwin’s Evolution: Solving the Species Puzzle Through Time and Place is a refreshing look at Darwin’s voyage incorporating this perspective.

From the Publisher:

In On the Origin of Species (1859), Charles Darwin presented his evidence for evolution and natural selection as its mechanism. He drew upon his earliest data gathered during his voyage on the HMS Beagle, which included collecting mammalian fossils in South America clearly related to living forms, tracing the geographical distributions of living species across South America, and sampling the peculiar fauna of the geologically young Galápagos Archipelago that showed evident affinities to South American forms. By the end of the voyage, he came to the realization that instead of various centers of creation, species evolved in different regions throughout the world. However, except for some personal ponderings, he did not express this revelation explicitly in his notebooks until shortly after his return. Over the years, he collected more evidence supporting evolution, but his early work remained paramount: it became the first paragraph of On the Origin of Species and encompassed three separate chapters, as well as later appearing in his autobiography.

Many discussions of Darwin’s landmark book give scant attention to this wealth of evidence and today we still do not fully appreciate its significance in Darwin’s thinking. In Origins of Darwin’s Evolution, J. David Archibald explores this lapse. He also shows that Darwin’s other early passion, geology, proved a more elusive corroboration of evolution. On the Origin of Species dedicated only one chapter to the rock and fossil record, as it appeared too incomplete for Darwin’s evidentiary standards. Carefully retracing Darwin’s gathering of evidence and the evolution of his thinking, Origins of Darwin’s Evolution achieves a new understanding of how Darwin crafted his transformative theory.

This is a well written, relatively short, monograph that that emphasizes the role of Historical Biogeography in Darwin’s thinking, by an experienced and well informed American paleontologist, who also wrote Extinction and Radiation: How the Fall of Dinosaurs Led to the Rise of Mammals and Dinosaur Extinction and the End of an Era.

A 245 million-year-old fossil horseshoe crab recently discovered in Idaho has been named Vaderlimulus because the animal’s shield head resembles the helmet worn by Darth Vader from the Star Wars film series. Paleontologists from the New Mexico Museum of Natural History and Science in Albuquerque (Allan J Lerner, Spencer G. Lucas) and the University of Colorado at Denver (Martin Lockley) just published a scientific article describing the extinct fossil horseshoe crab. Their findings were published in the latest issue of the German paleontological journal Neues Jahrbuch für Geologie und Paläontologie, which is the world’s oldest paleontological journal.

Vaderlimulus is the first North American fossil horseshoe crab from rocks of the Triassic Period. The Triassic was the first period of the Mesozoic Era (252 to 201 million years ago). Dinosaurs and mammals were just beginning their evolutionary development during the Triassic, but horseshoe crabs were already ancient by that time. Their fossil record dates back at least 470 million years ago, but fossils of horseshoe crabs are generally rare. When horseshoe crab fossils are found they are often new to science, as is the case with Vaderlimulus.

There are only four species of horseshoe crabs alive today, and their populations are decreasing. They are not true crabs but are more closely related to scorpions and spiders. Modern horseshoe crabs are often considered ‘living fossils’ due to having shown little apparent change in physical appearance over a vast period of geologic time.

“Vaderlimulus, however, has unusual body proportions that give it an odd appearance,” said lead author Allan J Lerner. This in part led the paleontological team to conclude that Vaderlimulus belonged to an extinct family, the Austrolimulidae. Members of this family were expanding their ecological range from marine into freshwater settings during the Triassic and often exhibit body modifications that provide them with a bizarre appearance by modern standards.

Every single regular reader of this blog SHOULD want to read, or should have already read, Mary Doria Russell’s excellent binary set including The Sparrow: A Novel and Children of God. (The Sparrow is first, COG second.)

Right now, and I assume very temporarily, The Sparrow is also avaialble for $1.99.

A quick word about the Sparrow series. It has been classified as science fiction. Others have said, no, it is not science fiction, it is philosophy and spirituality. A lot of church groups read it because of its religious meaning and implications.

That is really funny because there isn’t a drop of religiosity in this series. There is a priest, but it is a priest mainly operating in a post-religion world. This series is primarily anthropology fiction, which happens to be set in a science fiction theme, and if anything, it deconstructs the central role of religious institutions and makes them look as potentially lame and potentially nefarious and as potentially impotent as the other institutions. Or, really, as products of human behavior as anthropologists understand it, the outcome of a mix of self interested behavior, bonding or revulsion, racism and in-group vs. out-group thinking, the power of institutions, ritual, tradition, class, and exploitation. Set, of course, in the background of co-evolution of morphology of predator and prey. There is also a linguistic theme addressing meaning creation (or lack there of: ouch), development of mind and behavior, language learning, and so on.

You have to read them, and now you can get one of them for two bucks! (Unfortunately COG seems regular price.)

Let me add this too, just noticed it, could be of interest for two bucks: The Science of Star Wars: The Scientific Facts Behind the Force, Space Travel, and More!.