Why was Darwin's Finch argument valid considering Weismann's argument?

Question

According to Darwin, there was only 1 species of Finch bird in Galapagos. Then Darwin argued that due to diet adaptation and natural selection, their beak changes causing new species--which is confirmed by John Gauld at the Geological Society of London.

In contrast, Weismann's and his mouse proofed that environment factor won't effect next generations.

Don't Weismann's argument contradicts Darwin? Ok, say that the Finch bird adapts (and killing the one who don't) with their diet. Their beak changes. But when these Finch bird breeds, their new generation's beak should reset to normal beak again.

The reason I asked this reason is because one article said that our teeth are changing due to overbites using utensils(1). However, not everyone use eating utensils. Indian mostly used finger. Indonesian don't really care whether we use our hand or spoon. If this trend keeps happening in the future, won't human evolve into two species? Homo sapien and Homo spoon (pun intended.)

Or am I mixing Darwin with Lamarck?

(1):http://www.theatlantic.com/health/archive/2013/01/how-forks-gave-us-overbites-and-pots-saved-the-toothless/267252/

Answer 1

Weismann's mouse tail experiment showed that mouse tail length is not inherited, if the change in tail length was caused by mutilations, and there was an absence of selection pressure.

However, Darwin's finches represented a completely different idea of evolution. In this case, the beak size of the finches did in fact change, but this was not due to mutilation. The beak sizes of the finches changed because finches with lower fitness due to their beak sizes were selected against, leading to the beak size changing over time.

If the mice were instead selected for tail length by preventing the long-tailed mice from reproducing, then it is indeed possible that the mice would eventually evolve to have shorter tails, or even absent tails.

Similarly, if the finches had their beak sizes reduced artificially but their fitness preserved (for example, by grinding down their beaks and feeding them soft food that does not require large beaks to break), the finches would not be expected to evolve smaller beaks.

It is not clear which method is the one through which the evolution of the overbite occurred. It could be due to a change in relative fitness, but a case can also be made in which fitness was not a large factor.

Answer 2

You are confusing with Lamark, yes. Ironically enough, some epigenetic information does transfer some adaptations, (see citrus cold adaptations for a well-known example. If they freeze, they go sour and pass that on.) but the Lamark idea is mostly discredited, anymore.

Darwin promoted a very distinct idea: Creatures must pass on traits to their offspring from the set available in them, so the effect of the individual success effects the selection of traits in the population.

The sets of traits that better equip an individual to successfully spawn will tend to eventually outnumber lesser sets, due both to superior survival and more effective breeding. They'll make more children in the first place, and these will be less likely to die.

The result is a shift in availability of traits* towards the successful.(*heritable)

None of that requires any transfer of developed traits beyond any intrinsic ability to adapt or the mentioned epigenetic advantages that pass.

Mammalian milk-transferred immunities are not genetic and very much passed from mother to child from her body's own adaptations. The ability to do that is inherited genetically, but the information providing the adaptation advantage is not.

A mutation that mucked up that system would not be an advantage, so would usually be selected against.

As to the spoon:

First question is "which definition of species are you using?", which is not a pedantic question. If using the populations not interbreeding option, (among a few others) we're already many different species. If you're specifically thinking about genetic incompatibilities, well, that would require changes related to breeding.

Could that theoretically occur? Sure, but it's gonna need to happen to multiple individuals in a compatible way all at once or it would need to be progressively developed over time, or it can't pass on. That's highly unlikely.