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🔗 Physiology 🔗 Evolutionary biology

In evolutionary biology and evolutionary psychology, the Trivers–Willard hypothesis, formally proposed by Robert Trivers and Dan Willard in 1973, suggests that female mammals are able to adjust offspring sex ratio in response to their maternal condition. For example, it may predict greater parental investment in males by parents in "good conditions" and greater investment in females by parents in "poor conditions" (relative to parents in good condition). The reasoning for this prediction is as follows: Assume that parents have information on the sex of their offspring and can influence their survival differentially. While pressures exist to maintain sex ratios at 50%, evolution will favor local deviations from this if one sex has a likely greater reproductive payoff than is usual.

Trivers and Willard also identified a circumstance in which reproducing individuals might experience deviations from expected offspring reproductive value—namely, varying maternal condition. In polygynous species males may mate with multiple females and low-condition males will achieve fewer or no matings. Parents in relatively good condition would then be under selection for mutations causing production and investment in sons (rather than daughters), because of the increased chance of mating experienced by these good-condition sons. Mating with multiple females conveys a large reproductive benefit, whereas daughters could translate their condition into only smaller benefits. An opposite prediction holds for poor-condition parents—selection will favor production and investment in daughters, so long as daughters are likely to be mated, while sons in poor condition are likely to be out-competed by other males and end up with zero mates (i.e., those sons will be a reproductive dead end).

The hypothesis was used to explain why, for example, Red Deer mothers would produce more sons when they are in good condition, and more daughters when in poor condition. In polyandrous species where some females mate with multiple males (and others get no matings) and males mate with one/few females (i.e., "sex-role reversed" species), these predictions from the Trivers–Willard hypothesis are reversed: parents in good condition will invest in daughters in order to have a daughter that can out-compete other females to attract multiple males, whereas parents in poor condition will avoid investing in daughters who are likely to get out-competed and will instead invest in sons in order to gain at least some grandchildren.

"Condition" can be assessed in multiple ways, including body size, parasite loads, or dominance, which has also been shown in macaques (Macaca sylvanus) to affect the sex of offspring, with dominant females giving birth to more sons and non-dominant females giving birth to more daughters. Consequently, high-ranking females give birth to a higher proportion of males than those who are low-ranking.

In their original paper, Trivers and Willard were not yet aware of the biochemical mechanism for the occurrence of biased sex ratios. Eventually, however, Melissa Larson et al. (2001) proposed that a high level of circulating glucose in the mother's bloodstream may favor the survival of male blastocysts. This conclusion is based on the observed male-skewed survival rates (to expanded blastocyst stages) when bovine blastocysts were exposed to heightened levels of glucose. As blood glucose levels are highly correlated with access to high-quality food, blood glucose level may serve as a proxy for "maternal condition". Thus, heightened glucose functions as one possible biochemical mechanism for observed Trivers–Willard effects.

Wild and West published a paper describing a mathematical model built on the Trivers–Willard hypothesis that allows precise predictions of alterations in sex-ratio under different circumstances.

🔗 Birds

Wisdom is a wild female Laysan albatross. She is the oldest confirmed wild bird in the world as well as the oldest banded bird in the world.

🔗 Numbers

In number theory, a narcissistic number (also known as a pluperfect digital invariant (PPDI), an Armstrong number (after Michael F. Armstrong) or a plus perfect number) in a given number base ${\displaystyle b}$ is a number that is the sum of its own digits each raised to the power of the number of digits.

🔗 Biography

John Socha-Leialoha (born 1958) is a software developer best known for creating Norton Commander, the first orthodox file manager. The original Norton Commander was written for DOS. Over the years, Socha's design for file management has been extended and cloned many times.

John grew up in the woods of Wisconsin, earned a BS degree in Electrical Engineering from University of Wisconsin–Madison, and his PhD in Applied Physics from Cornell University. He now lives in Bellevue, Washington with his wife. His son, John Avi, is a graduate of the University of Washington.

Starting in September 2010, John began working at Microsoft officially.

🔗 Medicine 🔗 Death 🔗 Countries

The article documents lists of countries by average life expectancy at birth by various sources of estimates.

🔗 Typography

A California job case is a kind of type case: a compartmentalized wooden box used to store movable type used in letterpress printing. It was the most popular and accepted of the job case designs in America. The California job case took its name from the Pacific Coast location of the foundries that made the case popular.

The defining characteristic of the California job case is the layout, documented by J. L. Ringwalt in the American Encyclopaedia of Printing in 1871, as used by San Francisco printers. This modification of a previously popular case, the Italic, it was claimed reduced the compositor's hand travel as he set the pieces of type into his composing stick by more than half a mile per day. In the previous convention, upper- and lowercase type were kept in separate cases, or trays. This is why capital letters are called uppercase and the minuscules are lowercase. The combined case became popular during the western expansion of the United States in the 19th century.

🔗 Finance & Investment 🔗 Economics 🔗 Books 🔗 Skepticism

Extraordinary Popular Delusions and the Madness of Crowds is an early study of crowd psychology by Scottish journalist Charles Mackay, first published in 1841 under the title Memoirs of Extraordinary Popular Delusions. The book was published in three volumes: "National Delusions", "Peculiar Follies", and "Philosophical Delusions". A second edition appeared in 1852, reorganizing the three volumes into two and adding numerous engravings. Mackay was an accomplished teller of stories, though he wrote in a journalistic and somewhat sensational style.

The subjects of Mackay's debunking include alchemy, crusades, duels, economic bubbles, fortune-telling, haunted houses, the Drummer of Tedworth, the influence of politics and religion on the shapes of beards and hair, magnetisers (influence of imagination in curing disease), murder through poisoning, prophecies, popular admiration of great thieves, popular follies of great cities, and relics. Present-day writers on economics, such as Michael Lewis and Andrew Tobias, laud the three chapters on economic bubbles.

In later editions, Mackay added a footnote referencing the Railway Mania of the 1840s as another "popular delusion" which was at least as important as the South Sea Bubble. In the 21st century, the mathematician Andrew Odlyzko pointed out, in a published lecture, that Mackay himself played a role in this economic bubble; as a leader writer in The Glasgow Argus, Mackay wrote on 2 October 1845: "There is no reason whatever to fear a crash".

🔗 Lists 🔗 Geography 🔗 Rivers

This article lists rivers by their average discharge measured in descending order of their water flow rate. Here, only those rivers whose discharge is more than 2,000 m³/s (71,000 cu ft/s) are shown, as this list does not include rivers with a water flow rate of less than 2,000 m³/s (71,000 cu ft/s). It can be thought of as a list of the biggest rivers on earth, measured by a specific metric.

For context, the volume of an Olympic-size swimming pool is 2,500 m³. The average flow rate at the mouth of the Amazon is sufficient to fill more than 83 such pools each second. The average flow of all the rivers in this list adds up to 1,192,134 m³/s.

🔗 Internet culture

In Internet culture, the 1% rule is a rule of thumb pertaining to participation in an internet community, stating that only 1% of the users of a website add content, while the other 99% of the participants only lurk. Variants include the 1–9–90 rule (sometimes 90–9–1 principle or the 89:10:1 ratio), which states that in a collaborative website such as a wiki, 90% of the participants of a community only consume content, 9% of the participants change or update content, and 1% of the participants add content.

Similar rules are known in information science, such as the 80/20 rule known as the Pareto principle, that 20 percent of a group will produce 80 percent of the activity, however the activity may be defined.

🔗 Computing 🔗 Computing/Computer hardware

The Dadda multiplier is a hardware binary multiplier design invented by computer scientist Luigi Dadda in 1965. It uses a selection of full and half adders to sum the partial products in stages (the Dadda tree or Dadda reduction) until two numbers are left. The design is similar to the Wallace multiplier, but the different reduction tree reduces the required number of gates (for all but the smallest operand sizes) and makes it slightly faster (for all operand sizes).

Dadda and Wallace multipliers have the same three steps for two bit strings ${\displaystyle w_{1}}$ and ${\displaystyle w_{2}}$ of lengths ${\displaystyle \ell _{1}}$ and ${\displaystyle \ell _{2}}$ respectively:

1. Multiply (logical AND) each bit of ${\displaystyle w_{1}}$, by each bit of ${\displaystyle w_{2}}$, yielding ${\displaystyle \ell _{1}\cdot \ell _{2}}$ results, grouped by weight in columns
2. Reduce the number of partial products by stages of full and half adders until we are left with at most two bits of each weight.
3. Add the final result with a conventional adder.

As with the Wallace multiplier, the multiplication products of the first step carry different weights reflecting the magnitude of the original bit values in the multiplication. For example, the product of bits ${\displaystyle a_{n}b_{m}}$ has weight ${\displaystyle n+m}$.

Unlike Wallace multipliers that reduce as much as possible on each layer, Dadda multipliers attempt to minimize the number of gates used, as well as input/output delay. Because of this, Dadda multipliers have a less expensive reduction phase, but the final numbers may be a few bits longer, thus requiring slightly bigger adders.