Tara

I understand that not all traits are adaptations, but is natural selection the only way adaptation can occur?

Also , is it correct to say that evolution is "fact"?

thanks

SimplyAtheistic

Firstly, adaptation as a temporary change is quite real. For example, if you lose your eyesight, your hearing becomes more acute, or if you lose the use of your legs, your upper body becomes stronger (if you use it regularly). These are temporary adaptations that only occur for that individual and will not be passed down to their children. Now genome adaptations are really just the results of natural selection. It all relies on random gene mutations, and the ones that have adapted the best (by random chance) survive. This reminds me of a fundy science teacher I had in 8th grade (2 years ago!) who made an example of how evolution was supposedly wrong. He pointed out that a giraffe has a special function in its heart to keep it alive while it dips its neck down for a drink, and he claimed that since it would have died without it, it couldn't have lived to pass on the adaption of the special structure in its heart to keep it alive. This is a gross misunderstanding most christians seem to have about evolution. Evolution is not a change that one can know of or try and control, it has to be a random gene mutation. Evolution is not fact, but it is the most plausible explanation, and the one most intelligent people would consider the right one.
Jake

Asha'man

Hi Tara,

I’m not sure exactly what you are asking. Natural selection is a reason for some traits to survive while others cease to exist.

It depends on what exactly you mean by evolution.

The idea of common descent is considered a scientific fact.
The existence of the various mechanisms that drive evolution (mutation & natural selection) is also a fact.
The process of one species changing over time, and also splitting into multiple species, is also an observed fact.

However, the assembly of all these components, and they exact way they are understood, is really a scientific theory. (Note: a scientific theory is not a guess, it is a method of understanding observations that yields testable predictions) This theory has been extensively tested, and has proven to be the only viable explanation for the diversity of life that we observe today. There are no legitimate challenges to this theory.

Embedded within the overall theory of evolution are many smaller theories. Each one addresses specific mechanisms, processes, and history. Some of these smaller theories are still being refined, and may eventually be proved to be false trails. However, a flawed understanding of a portion of the process does not falsify the overall system.

Tara

I did mean genome adaptation, sorry about that...

I was being called out for refering to evolution as fact, but it is in a sense.

"Well evolution is a theory. It is also a fact. And facts and theories are different things, not rungs in a hierarchy of increasing certainty. Facts are the world's data. Theories are structures of ideas that explain and interpret facts. Facts don't go away when scientists debate rival theories to explain them. Einstein's theory of gravitation replaced Newton's in this century, but apples didn't suspend themselves in midair, pending the outcome. And humans evolved from ape-like ancestors whether they did so by Darwin's proposed mechanism or by some other yet to be discovered.

Moreover, "fact" doesn't mean "absolute certainty"; there ain't no such animal in an exciting and complex world. The final proofs of logic and mathematics flow deductively from stated premises and achieve certainty only because they are not about the empirical world. Evolutionists make no claim for perpetual truth, though creationists often do (and then attack us falsely for a style of argument that they themselves favor). In science "fact" can only mean "confirmed to such a degree that it would be perverse to withhold provisional consent." I suppose that apples might start to rise tomorrow, but the possibility does not merit equal time in physics classrooms."

- Stephen J. Gould, " Evolution as Fact and Theory"; Discover, May 1981

Tara

Well, traits are either adaptations, byproducts of those adaptations or random "noise", right?

If it wasn't for natural selection would organisms have any capacity to adapt (genome wise) to their environment? Isn't the only way for evolution to occur through natural selection?

That seems too simple, what am I missing?


This makes a lot of sense, thanks!

Non-praying Mantis

Evolution can occur in several ways, but I am not sure if it would be correct to call the peacock's tail an adaptation. Is the size of a head of letucce (produced by artificial selection) an adaptation? Natural selection is only one way that evolution can occur, but I think that the definition of adaptation requires natural selection to be the cause.

Actually, what you describe, Jake, is adaption, not adaptation. A single organism can adapt to its environment over its lifespan, but these changes do not get passed to its offspring as you said. Only populations of organisms can evolve.

NPM

Tara

I don't understand this point entirely. How is a peacock (not a domestic animal?) comparable to an artificially selected head of lettuce?

I don't think all artificially selected traits can be called "adaptations" because "adaptation" implies that the change improves the individual or species' fitness in relationship to its environment. And artificially selected traits don't necessairly do that, although in some cases they do, like pest-resistance in crops.

hmmm....So I'm not sure.

good distinction, I didn't think of that.

Wounded King

I think NPMs point was that Peacocks tails are an example of sexual selection, which is artificial in as much as it is a choice by the female peacock as to who she wishes to mate with. Sexually selected traits are often detrimental to an organisms general fitness but make up for it by increasing their reproductive fitness in terms of mating success.

Tara

okay, gottcha, thanks...

Dr Rick

Though evolution is a well-established and supported theory, many issues still remain. Take sexual selection as an example:

Sex and gender scientists explore a revolution in evolution:

"Darwin may have been wrong about sex. Or at least too narrow minded.

At the annual meeting of the American Association for the Advancement of Science, leading researchers and theorists in the evolution of sexual behavior will gather to present the growing evidence that Darwin's idea of sexual selection requires sweeping revisions...Darwin's theories of natural selection are well established and generally accepted: ''Survival of the fittest'' leads to the evolution of a particular species over time, and species evolve from other species.

But a third theory has piggybacked upon the success of these other two: Darwin's theory of sexual selection. Sexual selection explains the evolution of physical and behavioral traits that increase the odds that an animal will reproduce. These same traits do not necessarily help the animal survive, as do naturally selected traits. The male praying mantis, for example, will sacrifice himself for love - the female begins to eat him even as they copulate. He doesn't survive long after finding his mate, but he does pass on his genes.

Darwin postulated that females are ''coy,'' mating rarely and choosing their mates carefully, presumably betting their odds on the males with the best genes to contribute to their offspring. For their part, males are ''ardent'' and promiscuous, and fight amongst themselves for female partners.

Later theories added that males are promiscuous because they have less to lose by making babies - unlike eggs, sperm are plentiful and small. Plus, females usually do most of the work to raise the offspring.

Sexual selection theory helped Darwin explain many traits, especially in males, that otherwise seemed maladaptive. The unwieldy tail on the male peacock, for instance, makes him more vulnerable to predators but more attractive to females.

Many behaviors do not fit sexual selection theory, however.

Says Vasey of his work with Japanese macaques: ''I see females competing for males all the time. I see males ignoring females that are desperate to copulate with them.''

A great deal of empirical evidence exists that refutes Darwinian sexual selection...For instance, anthropologist Sarah Hrdy studied langur monkeys in the 1980s and found that females promiscuously mate with many males...Homosexual behavior is common but unexplained by Darwin. Over 300 vertebrates, including monkeys, flamingoes and male sheep, practice homosexual behavior.Homosexual behavior is common but unexplained by Darwin. Over 300 vertebrates, including monkeys, flamingoes and male sheep, practice homosexual behavior...In female Japanese macaques, homosexual behavior appears to have evolved from female strategies to coerce reticent males to mate with them. Eager females will mount unwilling males and prompt them to mate with them - a strategy that was easily expanded to mounting other females. Despite these evolutionary origins, however, homosexual behavior among Japanese macaques may have no adaptive value.

The whole context for Darwin's theory of sexual selection is dissolving,'' says Roughgarden. ''So, Darwin is incorrect in the particulars, but more importantly, [his theory of sexual selection] is inadequate even as an approach.''

Both Roughgarden and Gowaty think it's time for a revolution, but not everyone agrees.

''This may be better viewed as a refinement of Darwinian theory, rather than a revolution,'' says Warner.

Vasey agrees, however, that something has to give: ''What I'm seeing, in my one species [macaques], is an unbelievable amount of sexual diversity that is very common. I see it every day, and traditional evolutionary theories for sexual behavior are inadequate and impoverished to account for what is going on.''

What conclusions can we draw about gender and sexual diversity in humans from such findings? Both Vasey and Roughgarden caution strongly against extrapolating animal behavior to humans, as evolutionary psychologists have done for decades.

''People often look to animals to decide for themselves what's natural and what's not natural,'' says Vasey. ''I don't think that's necessarily a good thing to do. I mean, animals engage in cannibalism and infanticide. They also don't take care of elderly individuals. Just because animals do something doesn't make it right or wrong.''

Rick