the-psoriasis-treatment

Let us assume that we collected data on the presence or absence of a trait (e.g., propensity toward risky behavior) in a population of individuals, as well as on intermediate effects of the trait, downstream effects on mating and survival success, and ultimately on reproductive success (a.k.a. “fitness”, in evolutionary biology). The data would have been collected over several generations. Let us also assume that we conducted a multivariate analysis on this data, of the same type as the analyses employing WarpPLS that were discussed here in previous posts ( ). The results are summarized through the graph below. Each of the numbers next to the arrows in the graph below represents the strength of a cause-effect relationship. The number .244 linking “a” and “y” means that a one standard deviation variation in “a” causes a .244 standard deviation increase in “y”. It also means that a one standard deviation variation in “a” causes a 24.4 percent increase in “y” considering the average “y”...

This post is a revised version of a previous post . The original post has been or will be deleted, with the comments preserved. Typically this is done with posts that attract many visits at the time they are published, and whose topics become particularly relevant or need to be re-addressed at a later date. *** We all evolved from one single-celled organism that lived billions of years ago. I don’t see why this is so hard for some people to believe, given that all of us also developed from a single fertilized cell in just 9 months. However, our most recent common ancestor is not that first single-celled organism, nor is it the first Homo sapiens, or even the first Cro-Magnon. The majority of the people who read this blog probably share a common ancestor who lived no more than 640 years ago. Genealogical records often reveal interesting connections - the figure below has been cropped from a larger one from Pinterest . You and I, whoever you are, have each two parents. Each of our parent...

There are two forms of familial hypercholesteromia (FH), namely heterozygous and homozygous FH. In heterozygous FH only one copy of the gene that causes it is present, inherited either from the father or the mother. In homozygous FH, which is the most lethal form, two copies of the gene are present. FH is associated with early-onset cardiovascular disease (CVD). Homozygous FH may happen if both the father and mother have heterozygous or homozygous FH. If both the father and mother have heterozygous FH, the likelihood that at least one in four children will have homozygous FH will be high. If both parents have homozygous FH the likelihood that all children will have homozygous FH will be high. In fact, in the latter case, homozygous FH in the children is almost certain. One case in which it won’t occur is if the combining FH gene from the father or mother mutates into a non-FH gene before it is used in the assembly of the genome of the child. A gene mutation in a specific locus, only ...

This post has been revised and re-published . The original comments are preserved below. Typically this is done with posts that attract many visits at the time they are published, and whose topics become particularly relevant or need to be re-addressed at a later date.

Genes do not evolve, nor do traits that are coded for our genes. We say that they evolve to facilitate discourse, which is alright. Populations evolve. A new genotype appears in a population and then either spreads or disappears. If it spreads, then the population is said to be evolving with respect to that genotype. A genotype may spread to an entire population; in population genetics, this is called “fixation”. (Human chromosomes capped by telomeres, the white areas at the ends. Telomere shortening is caused by oxidative stress, and seems to be associated with death of cells and organisms. Source: Wikipedia.) Asexual reproduction is very uncommon among animals. The most accepted theory to explain this is that animal populations live in environments that change very quickly, and thus need a great deal of genetic diversity within them to cope with the change. Otherwise they disappear, and so do their genes. Asexual reproduction leads to dramatically less genetic diversity in population...

Most human traits (e.g., body fat percentage, blood pressure, propensity toward depression) are influenced by our genes; some more than others. The vast majority of traits are also influenced by environmental factors, the “nurture” part of the “nature-nurture” equation. Very few traits are “innate”, such as blood type. This means that manipulating environmental factors, such as diet and lifestyle, can strongly influence how the traits are finally expressed in humans. But each individual tends to respond differently to diet and lifestyle changes, because each individual is unique in terms of his or her combination of “nature” and “nurture”. Even identical twins are different in that respect. When plotted, traits that are influenced by our genes are distributed along a bell-shaped curve. For example, a trait like body fat percentage, when measured in a population of 1000 individuals, will yield a distribution of values that will look like a bell-shaped distribution. This type of distribu...

There are human traits that evolved in spite of being survival handicaps. These counterintuitive traits are often called costly traits, or Zahavian traits (in animal signaling contexts), in honor of the evolutionary biologist Amotz Zahavi (Zahavi & Zahavi, 1997). I have written a post about this type of traits, and also an academic article (Kock, 2009). The full references and links to these publications are at the end of this post. The classic example of costly trait is the peacock’s train, which is used by males to signal health to females. (Figure below from: animals.howstuffworks.com.) The male peacock’s train (often incorrectly called “tail”) is a costly trait because it impairs the ability of a male to flee predators. It decreases a male’s survival success, even though it has a positive net effect on the male’s reproductive success (i.e., the number of offspring it generates). It is used in sexual selection; the females find big and brightly colored trains with many eye spot...

As noted in this post , it is possible for a food-related trait to evolve to fixation in an entire population in as little as 396 years; not the millions of years that some believe are necessary for mutations to spread. Moreover, evolution through fixation can occur in the absence of any selective pressure. That is, traits that are neutral with respect to fitness may evolve by chance, particularly in small populations. (A group of 100 individuals who made it to the Americas after a long and grueling trek would fit the bill.) This rather counterintuitive phenomenon is known as genetic drift (Hartl & Clark, 2007; Maynard Smith, 1998). Fast evolution of traits certainly applies to polygenic traits, such as traits associated with nutrient metabolism. Polygenic traits are traits that are influenced by multiple genes, with those genes acting together to influence the expression of the trait. Moreover, a mutation in one single pleiotropic gene (a gene that influences various traits) can l...

Early hominid ancestors like the Australopithecines (e.g., Lucy ) were likely strict vegetarians. Meat consumption seems to have occurred at least occasionally among Homo habilis, with more widespread consumption among Homo erectus, and Homo sapiens (i.e., us). The figure below (from: becominghuman.org; click on it to enlarge) shows a depiction of the human lineage, according to a widely accepted theory developed by Ian Tattersall. As you can see, Neanderthals are on a different branch, and are not believed to have been part of the human lineage. Does the clear move toward increased meat consumption mean that a meat-only diet is optimal for you? The answer is “perhaps”; especially if your ancestors were Inuit and you retained their genetic adaptations. Food specialization tends to increase the chances of extinction of a species, because changes in the environment may lead to the elimination of a single food source, or a limited set of food sources. On a scale from highly specialized to...

Charles Darwin, perhaps one of the greatest scholars of all time, thought about his theory of mutation, inheritance, and selection of biological traits for more than 20 years, and finally published it as a book in 1859.  At that time, many animal breeders must have said something like this: “So what? We knew this already.” In fact George Washington, who died in 1799 (many years before Darwin ’s famous book came out), had tried his hand at what today would be called “genetic engineering.” He produced at least a few notable breeds of domestic animals through selective breeding. Those include a breed of giant mules – the “Mammoth Jackstock” breed. Those mules are so big and strong that they were used to pull large boats filled with coal along artificial canals in Pennsylvania . Washington learned the basic principles of animal breeding from others, who learned it from others, and so on. Animal breeding has a long tradition. So, not only did animal breeders, like George Washington, ha...

Often in discussions about Paleolithic nutrition, and books on the subject, we see speculations about how long it would take for a population to adapt to a particular type of food. Many speculations are way off mark; some think that even 10,000 years are not enough for evolution to take place. This post addresses the question: How long does it take for a food-related trait to evolve? We need a bit a Genetics 101 first, discussed below. For more details see, e.g., Hartl & Clark, 2007; and one of my favorites: Maynard Smith, 1998. Full references are provided at the end of this post. New gene-induced traits, including traits that affect nutrition, appear in populations through a deceptively simple process. A new genetic mutation appears in the population, usually in one single individual, and one of two things happens: (a) the genetic mutation disappears from the population; or (b) the genetic mutation spreads in the population. Evolution is a term that is generally used to refer to ...