Category Archives: Natural Selection

Reproductive Success and Fitness are not the same thing

Reproductive Success (RS) is defined in many ways in different places by different people, but one of the most common definitions is simply the number of offspring an individual produces. This definition is further modified in most cases to mean only those individuals that will be fertile, i.e., capable of producing further offspring. RS is important in understanding Natural Selection (NS). In the simplest model, a heritable feature that increases RS will be selected for over time in a population because individuals with higher RS will contribute more offspring to future generations and this, in turn, causes the frequency of the RS-enhancing allele (gene variant) to become more common over generational time in that population.

Fitness is a property of an allele that refers to its relative likelihood of representation in future generations in a population. An allele with higher fitness will be more likely to be represented in future generations within a population than an allele for the same gene with lower fitness. The important thing here is that the likelihood of future representation has to be due to a feature of that allele, and not random effects.

At first glance RS and Fitness are the same, or similar, but one might immediately notice that RS is a feature of an individual (that has offspring) while fitness is a feature of an allele. So, it is possible that a given individual will have a relatively high RS but contain a particular allele with low fitness. Presumably the higher RS of that individual is due to high-fitness alleles of other genes. In this way, fitness and RS are different, but when considering large scales of time and large populations, the two can be (perhaps) safely conflated because things average out over time and the different alleles are being independently assorted over generational time, so each allele gets to have its day, sometimes, independently of other lower-fitness alleles. By this way of thinking, RS and fitness can be safely considered as measures of roughly the same thing, but with caveats.

RS is usually measured, in actual experimental work or field observations, as the number of offspring observed for an individual, but to make sure that RS is correlated with fitness, one might measure grand-offspring in order to factor out infertile offspring and other factors that may affect one generation but that do not apply over the long term. Again, RS and fitness are then, it would seem, equatable but with caveats.

RS is the number of offspring or grand-offspring but kin selection may apply as well. This is where an individual foregoes some of its own reproduction for the benefit of a relative, causing indirect fitness, a measure of this contribution devalued by the probability of the two individuals sharing the same allele by common descent. One can state that a measure of RS is still a measure of fitness because over the long term, again, things average out, but equating fitness and RS is done, again, with caveats.

There may be an optimal number of offspring an individual may have, above which longer term reproduction is reduced. A litter that is too large may result in a set of adults that are smaller than ideal and will thus have fewer offspring, or in the case of serial reproduction, if parental investment is spread out over several offspring, having too many offspring in a row may cause a deficit for all of the offspring, or for the later offspring that get less care because less energy is available, or earlier offspring may get short changed by being left on their own sooner. Putting this another way, the ultimate long-germ fitness strategy may be to have X offspring, where having more or fewer than X results in a suboptimal outcome. In this way, increasing RS from zero towards X increases fitness, but increasing RS beyond X decreases fitness.

So, RS equals fitness except:

  • RS is a measure applied to an individual while fitness is ideally applied to alleles for a gene or some other genetic construct;
  • The offspring-fertility link can be misleading. A queen bee with an allele that allows her to produces more sterile offspring may also produce more fertile offspring;
  • RS is fitness plus or minus random effects;
  • RS usually does not consider indirect fitness;
  • RS is selected to be optimized while fitness is selected to be maximized.

Equating RS and fitness is therefore only a rough approximation. When initially learning about Natural Selection students are often led to believe that RS and fitness are the same, which is only true with these (and possibly other) caveats. Equating RS and fitness in pedagogy risks skipping past and perhaps never understanding the caveats, and these caveats are very far from trivial. They are, in many cases, the point of specific evolutionary research projects.

“A new theory of evolution proves what Sarah Palin has always known: Darwin was a retard”

As I predicted earlier today, various journalists are taking up the theme that “Darwin was wrong” because he did not predict that niches into which organisms evolved would be a major controlling feature in the overall pattern of evolution.

But of course, he did, and the new research being referred to does not “disprove darwin.”

At least the piece I’m referring to here takes a somewhat tongue in cheek attitude towards the story.

Continue reading “A new theory of evolution proves what Sarah Palin has always known: Darwin was a retard”

Natural Selection vs. Opportunity in Macroevolutionary Patterning of the Fossil Record

This post was chosen as an Editor's Selection for ResearchBlogging.orgI’m going to talk about one or two peer reviewed papers, but in doing so, I’m going to have to say a few words … and this will not be pretty … about a certain science writer’s report at the BBC.

In an article titled “Space is the final frontier for evolution, study claims” BBC “science writer” Howard Falcon-Lang uses the old, tired, and quite frankly, stupendously unethical tack of making a claim that Darwin has been overthrown by new research. If someone actually overthrows Darwin, then so be it. But this is not what has happened. Falcon-Lang, or perhaps his BBC handlers, have used the cheap trick to sell their wares, and this is not appreciated.

If Howard Falcon-Lang did not a) claim to be a science reporter and b) have a dumb-ass hyphenated name, I’d be nice in my critique of his recent writeup. But no. He left me no choice. I will have to take it apart red in tooth and claw.

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The Modes of Natural Selection

There many ways of dividing up and categorizing Natural Selection. For example, there are the trichotomies of Natural Selection, Sexual Selection and Artificial Selection, and Modes of Selection (Stabilizing, Directional, and Disruptive) trichotomy.

We sense that these are good because they are “threes” and “three” is a magic number. Here, I’m focusing on the Mode Trichotomy, and asking that we consider that there are not three, but four modes of Natural Selection. This will cause tremors throughout the Evolutionary Theory community because Four is not a magic number, but so be it.
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The Three Necessary and Sufficient Conditions of Natural Selection

Natural Selection is the key creative force in evolution. Natural selection, together with specific histories of populations (species) and adaptations, is responsible for the design of organisms. Most people have some idea of what Natural Selection is. However, it is easy to make conceptual errors when thinking about this important force of nature. One way to improve how we think about a concept like this is to carefully exam its formal definition.

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…)

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The Natural Basis for Inequality of the Sexes

Is the Natural World a valid source of guidance for our behavior, morals, ethics, and other more mundane areas of thought such as how to build an airplane and what to eat for breakfast?1 When it comes to airplanes, you’d better be a servant to the rules of nature (such as gravity) or the airplane will go splat. When it comes to breakfast, it has been shown that knowing about our evolutionary history can be a more efficacious guide to good nutrition than the research employed by the FDA, but you can live without this approach and following FDA guidelines will not do you in. A naturalistic approach can work when it comes to behavior too, but there are consequences. You or someone you love would probably not like the consequences.
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BBC: DNA mutations followed by selection does not lead to new species!?!?

In an BBC article describing a Royal Society paper on the rate of mutation in warm vs. cooler climates, the BBC made this statement:

DNA can mutate and change imperceptibly every time a cell divides and makes a copy of itself.

But when one of these mutations causes a change that is advantageous for the animal – for example, rendering it resistant to a particular disease – it is often “selected for”, or passed down to the next few generations of that same species.

Such changes, which create differences within a population but do not give rise to new species, are known as “microevolution”.

I suppose the BBC is into the Hopeful Monster theory or something.

Read it here, come back, and fight it out.

Ultimate Causes, Proximate Mechanisms

Why does a soldier throw himself on a hand grenade to save the lives of a half-dozen unrelated fellow soldiers? Why does someone run into a burning building they happen to be passing to save a child they don’t know? From a Darwinian perspective these seem to be enigmatic behaviors that would “select against” such individuals (or more properly, select against the heritable component of this behavior).

There are several possible explanations for this….
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