Saturday, June 17, 2006

Secrets of Bat Machismo From Discover magazine, May 2006, p. 17: A species of bat has been discovered with very large testicles and very small brains. This is explained as follows: "Testicles are almost always bigger in animals species in which females mate with multiple partners.... When females are promiscuous, the sperm of different males must compete to fertilize each egg. Because males with more sperm have a better chance of producing offspring, the frequency of large testicles in those species increases. The pattern holds among all animals, including primates. Gorillas, who keep their harem close, have small testicles, while libertine chimpanzees have large ones. Those of humans, whose mating habits fall in between, are midsize."

The connection to brain size is that both a large brain and large testicles take a lot of metabolic resources. So we would expect that bats that need big testicles to gain an advantage in reproducing would have smaller brains to compensate.

Evidence was collected for 334 bat species. "In species with unfaithful females, males invest almost five times as much in testicles and 27 percent less in brains."
Origin of the Ear From Discover magazine, May 2006, p. 16: "Our earliest ancestors may have breathed through their ears." "The tubes that form the middle-ear canal in humans probably evolved from a pairof gill-like holes that allowed primeval sea creatures to breathe from the back of their heads."

The evidence: fossils dated at 370 million years ago of an intermediate species between fish and the first four-limbed animals to crawl onto land. This species "had small bones in its skull that appear to be early analogues of both ear canals and the gill system in some modern fish." When the creatures evolved to walk on land and breath air through the mouth, the canals were no longer needed for breathing, could develop into ears.
From Discover Magazine, May 2006, p. 13: Are We All Asians?

While most biologists agree that humans have evolved from earlier species of primates, this article points out that the location of these early ancestors of humans is not established. Some believe the evolution occurred in Africa and that humans spread elsewhere relatively late (80,000 years ago). Two scientists, Robin Dennell and Wil Roebroeks, suggest that we don't have enough evidence from Asia to discount it as a starting point for human evolution.

Another scientist, Spencer Wells, supports the Africa hypothesis, but added, "That Homo erectus could have origins in Asia would be potentially shocking, but I think that what Roebroeks and Dennell are saying reflects the state of the field. We certainly don't have enough fossils. Perhaps we are never going to be able to test the hypothesis."

This shows how open scientists are to having their favored interpretation of the evidence overturned by new evidence. It is how science advances.

Note that if new evidence turns up for humans evolving in Asia, it would not discredit the idea of evolution, only a prominant hypothesis about a particular detail of it.
Introduction: Evolution Defined

One popular misconception perpetrated by intelligent design proponants and creationists is that evolution is "just a theory," implying a significant degree of uncertainty. There are two aspects to correcting this misconception.

First, evolution is not in any sense a theory, speaking strictly of the concept of evolution. Evolution refers to a type of change that has nothing theoretical about it, any more than the concept of velocity is a theory. Velocity refers to an observable phenomena associated with motion. Evolution refers to a method by which certain changes can come about in a certain type of population. One can point to many examples of it, and one can create any number of examples in computer simulations. Evolution happens.

Evolution happens under the following circumstances:

1) One has a population of entities which are nearly, but not completely, identical.
2) These entities reproduce or are reproduced such that the copies are nearly, but not completely, identical to the original. Earlier members of the reproducing population are eventually replaced by these copies.
3) There is something about the situation which causes certain individuals of the population to produce more copies of themselves than other members. This happens consistently over a number of generations.
4) The differences in reproductive rates eventually brings about a change to the general characteristics of the population compared to an earlier generation.

Examples: One could write a program which starts with a set of 1000 numbers, each number between 1 and 100. The program picks a number from the set at random and evaluates whether or not the number is prime or not. If the number is prime, the program copies the number twice into a new number storage area. If the number is not prime, it is reproduced just once in the new area. Once the new area has 1000 numbers, the program starts again with the new set of numbers. Each iteration of the program will generate a new set of 1000 numbers. If this is kept up long enough, one would find almost all the numbers in the latest set to be prime numbers, even if the original set had only a nominal number of primes.

Other examples include selective breeding of dog or horses to produce animals with a certain trait, competition in the marketplace which over time changes the features on a product such as telephones. Even ideas evolve. Ideas exist in people's heads or minds, and are reproduced as new people are born and are exposed to the ideas. Ideas like racism were once very common, but today, the idea is found less and less.

This is not controversial. But when most people hear the word evolution, they think of the evolution of the species. This refers to the theory that the differences in animal and plant species that we observe in the world today are the result of a process of evolution. In this case, the population of entities is a biological creature such as a redwood tree or a robin or a dolphin. These populations reproduce by way of copulation and giving birth to new members, who grow up to replace the parents. Most dolphins are very similar to each other, but not identical. The selection occurs when the environment changes so that creatures with some feature have a better than average chance of surviving and reproducing than other members. For example, members of the species with a particular coloration might prove harder to see in the new environment, meaning they get captured by predators less frequently and so reproduce more frequently. The gene that produces the coloration is more common in the next generation, so more of the offspring have the coloration. The process can lead to the entire population changing from one color to another.

The mechanism of evolution is perfectly logical. The only thing theoretical was (back when the theory was first proposed) whether or not the differences in creatures actually observed could be explained by environmental selection. Over time, more and more evidence has been found to support the theory of evolution of species until now, evolution is considered the actual explanation for diversity of species. The only things in questions are particulars of how quickly changes can occur and the mechanical details.

This blog will be listing examples, hoping to demonstrate the reasonableness and value of this idea.

POSTING GUIDELINES: Please limit comments to the relevance of the particular example as evidence for natural selection as the explanation for the diversity of species. This is not the place to debate religious doctrine. (I'll have another blog where that will be appropriate.) Comments which are abusive will be deleted. Off-topic comments will be deleted.