Rhinocrisy

So, today, the NHTSA announced that it was pushing up CAFE standards for light trucks (for 2008-2011). This is good, especially since it’s been a full decade without any substantial tweaks in standards. The bad news: they’re creating SIX new categories of light trucks (based on their “footprint” size in square feet), each with their own average fuel economy requirement. So while the Ford Excursion and the Toyota RAV4 will have to become slightly more fuel-efficient by 2011, this also means that more Americans can start buying heavier cars without affecting manufacturer’s bottom line. While previously Ford had to sell an Escape (average 24 mpg for a 5-speed 4WD) for every Expedition (average 16 mpg for a 4WD) it sold, now it can sell as many as it wants of each. Meaning Ford is free to discontinue the Escape and sell only Expeditions without fear of penalties. And the U.S. fleet can migrate towards becoming even gassier.

PZ is lambasting Deepak Chopra today. Not for his New Age pseudo-Vedic/quantum mechanics mysticism spooge, but for his apparent anti-evolutionary stance. It’s worth pointing out something that I think goes little appreciated by anyone, especially those idiots arguing against selection all the time, which is how powerful natural selection really is.

Here’s some elementary population genetics: The basic meat of evolution is mutation followed by change in frequency of alleles. Let’s say we’re examining a particular position in the genome. Everyone in our species of interest has the same nucleotide at this position. Now, suppose one individual acquires a mutation here. If we have a breeding population of N_e diploid individuals, this means that mutation has a frequency of 1/2N_e. The probability of this mutation “fixing” in the population (that is, reaching 100% frequency) is:Here s is the “selective coefficient”, a measure of the deviation of the fitness of the individual with respect to the average fitness of the population. If the average individual produces n offspring, our mutant will produce n(1 + s) offspring. (Note that if s is zero, the mutation is selectively neutral and the fitness is the same.) For small s and large N, the above equation can be approximated as π = s.

What does this mean? Well, take our human population. We have a genome of about 3 billion bases. Typically this means about 100 new mutations per generation per individual. That is, your offspring will have a hundred completely novel changes to their genome. Most of the time this will mean nothing. Occasionally this will result in positively selected mutations. In a breeding population of 10,000 individuals (a relatively small population size, as our ancestors had), this provides millions of novel mutations every generation.

In other words, a novel mutation with even a small selective coefficient has a significant chance of being fixed. In the human population this means even mutations that produce marginal changes in fitness - a differential of 1001 to 1000 births per individual - will be fixed 0.1% of the time. A selective coefficient of 10^-2 is powerfully strong selection. And it occurs completely invisibly to us. We would never note its effects; we produce far fewer than 100 offspring, and this tiny differential would never be observed without a complex, rigorous survey. But by the time a mere 10 individuals have acquired this mutation, its fixation probability has already climbed to 10%.

So remember this: natural selection is a powerful, efficient method for sculpting species, much stronger than our intuition suggests.

It’s all fun and games until someone cuts out the middlemen.