Comatose said- I don't think anyone here in this discussion thinks only the best survives. There are lots of examples of slightly disadvantageous things evolving along with the good.
I've seen three posters in this thread alone who use language that conveys that evolution is an "upwards and onwards process": I'll leave it to you to figure out who. It's an idea I've seen in many other threads, and it's not the truth about evolution, but merely a child's version which actually interferes with understanding evolution based on the reality of what IS known about it.
Cofty said-
"Ratchet" as in the sense of accumulating mutations. In other words evolution doesn't have to do it all in one go. It is about the difference between single-step and cumulative selection. The "ratchet" of cumulative natural selection safeguards beneficial mutations in the gene pool - assuming the body that first hosts the mutation doesn't get eaten before it breeds.
That's utterly absurd, and yes, I'm aware that Richard Dawkins has used the "ratchet analogy" in his book, "Climbing Mt Improbable" (and in fact the analogy to climbing a mountian assumes a stepwise ratchet process). However, such a ratchet effect (i.e. one that prevents back mutations) hasn't been proven to exist, and where it HAS been shown, it only works by accumulation of deleterious mutations. NOT neutral or advantageous ones.
The closest concept in biology is "Muller's Ratchet", named after a geneticist who reported on the phenomena existing in asexual organisms where an accumulation of changes in genes via mutations could in fact demonstrate a "ratchet effect", except resulting in the accumulation of deleterious mutations within small populations; this could eventually lead to extinction, since it's a one-way ratchet, except running in reverse (unless positive mutations occurred to counteract).
In fact, that's why Muller proposed recombination of genes via sexual reproduction as a possible solution to overcome the "ratchet effect"; it's a way for organisms to AVOID a ratchet effect by weakening their impact on the organisms, due to infusion of alleles from the other person that don't code for the same trait.
And the fact is, bacteriologists will tell you that some species of bacteria avoid the "ratchet problem" by eg direct exchange of plasmids: it's basically a way to exchange genetic material with others (although no scientist has yet determined if the bacteria are enjoying swapping genetic material as much as with the sexual process, LOL!).
http://www.sciencedaily.com/releases/2012/08/120810083613.htm
From the article on a computer simulation they ran, genetistist Richard Neher:
These findings could explain the long-term maintenance of mitochondria, the so-called power plants of the cell that have their own genome and divide asexually. By and large, evolution is driven by random events or as Richard Neher says: "Evolutionary dynamics are very stochastic."
Obviously there's a sufficient overall gradient in the "slightly more-adapted" direction for evolution to work over multiple generations, since we have evolved, but there is no "ratchet effect" to lock in the improvements (or at least, if there is, it's a pretty weak-effect at best).
In fact, Huntington's Chorea is a disease which resulted from a spontaneous mutation of a gene in a woman who lived 200 years ago in Venezuela:
http://evolution.berkeley.edu/evolibrary/article/medicine_05
If there were a "ratchet effect" and evolution was all about getting "better", then such spontaneous mutations that result in diseases couldn't appear. The mutation is untouchable to elimination by natural selection, since it arises typically AFTER the individual has passed on the defective gene to their offspring.
Again, those looking for certainty in studying evolution might be better-advised to get comfortable with unpredictability and probabilities first, since that's what stochastic processes involve: random dumb luck and living with probabilities, not certainty.
Good news is we are ALL lucky to be the products of the one sperm to win the race to enter our mother's ovum, and we all are born with a first-place ribbon, LOL!
Cofty said- You have an uncanny knack of misrepresenting what others have written.
Misrepresenting? I don't think so....
Cofty said- When I complained about you being off-topic that was because you were waffling about ancient Hebrew culture.
I was responding to a challenge raised by Kate, and backing up the claim with references: do I have to seek your permission before doing so?
Adam