Summary

We should not expect evolution of complex psychological and cognitive adaptations in the timeframe in which, morphologically, animal bodies can only change by very little. The genetic alteration to the cognition for speech shouldn't be expected to be dramatically more complex than the alteration of vocal cords.

Evolutions that did not happen

When humans descended from trees and became bipedal, it would have been very advantageous to have an eye or two on back of the head, for detection of predators and to protect us against being back-stabbed by fellow humans. This is why all of us have an extra eye on the back of our heads, right? Ohh, we don't. Perhaps the mate selection resulted in the poor reproductive success of the back-eyed hominids. Perhaps the tribes would kill any mutant with eyes on the back.

There are pretty solid reasons why none the above has happened, and can't happen in such timeframes. The evolution does not happen simply because the trait is beneficial, or because there's a niche to be filled. A simple alteration to the DNA has to happen, causing a morphological change which results in some reproductive improvement; then DNA has to mutate again, etc. The unrelated nearly-neutral mutations may combine resulting in an unexpected change (for example, the wolves have many genes that alter their size; random selection of genes produces approximately normal distribution of the sizes; we can rapidly select smaller dogs utilizing the existing diversity). There's no such path rapidly leading up to an eye on back of the head. The eye on back of the head didn't evolve because evolution couldn't make that adaptation.

The speed of evolution is severely limited. The ways in which evolution can work, too, are very limited. In the time in which we humans have got down from the trees, we undergone rather minor adaptation in the shape of our bodies, as evident from the fossil record - and that is the degree of change we should expect in rest of our bodies including our brains.

The correct application of evolutionary theory should be entirely unable to account for outrageous hypothetical like extra eye on back of our heads (extra eye can evolve, of course, but would take very long time). Evolution is not magic. The power of scientific theory is that it can't explain everything, but only the things which are true - that's what makes scientific theory useful for finding the things that are true, in advance of observation. That is what gives science it's predictive power. That's what differentiates science from religion. The power of not explaining the wrong things.

Evolving the instincts

What do we think it would take to evolve a new innate instinct? To hard-wire a cognitive mechanism?

Groups of neurons have to connect in the new ways - the neurons on one side must express binding proteins, which would guide the axons towards them; the weights of the connections have to be adjusted. Majority of the genes expressed in neurons, affect all of the neurons; some affect just a group, but there is no known mechanism by which an entirely arbitrary group's bindings may be controlled from the DNA in 1 mutation. The difficulties are not unlike those of an extra eye. This, combined with above-mentioned speed constraints, imposes severe limitations on which sorts of wiring modifications humans could have evolved during the hunter gatherer environment, and ultimately the behaviours that could have evolved. Even very simple things - such as preference for particular body shape of the mates - have extreme hidden implementation complexity in terms of the DNA modifications leading up to the wiring leading up to the altered preferences. Wiring the brain for a specific cognitive fallacy is anything but simple. It may not always be as time consuming/impossible as adding an extra eye, but it is still no little feat.

Junk evolutionary psychology

It is extremely important to take into account the properties of evolutionary process when invoking evolution as explanation for traits and behaviours.

The evolutionary theory, as invoked in the evolutionary psychology, especially of the armchair variety, all too often is an universal explanation. It is magic that can explain anything equally well. Know of a fallacy of reasoning? Think up how it could have worked for the hunter gatherer, make a hypothesis, construct a flawed study across cultures, and publish.

No considerations are given for the strength of the advantage, for the size of 'mutation target', and for the mechanisms by which the mutation in the DNA would have resulted in the modification of the circuitry such as to result in the trait, nor to the gradual adaptability. All of that is glossed over entirely in common armchair evolutionary psychology, and unfortunately, even in the academia. The evolutionary psychology is littered with examples of traits which are alleged to have evolved over the same time during which we had barely adapted to walking upright.

It may be that when describing behaviours, a lot of complexity can be hidden into very simple-sounding concepts; and thus it seems like a good target for evolutionary explanation. But when you look at the details - the axons that have to find the targets; the gene must activate in the specific cells, but not others - there is a great deal of complexity in coding for even very simple traits.

Note: I originally did not intend to make an example of junk, for thou should not pick a strawman, but for sake of clarity, there is an example of what I would consider to be junk: the explanation of better performance at Wason Selection Task as result of evolved 'social contracts module', without a slightest consideration for what it might take, in terms of DNA, to code a Wason Selection Task solver circuit, nor for alternative plausible explanation, nor for a readily available fact that people can easily learn to solve Wason Selection Task correctly when taught - the fact which still implies general purpose learning, and the fact that high-IQ people can solve far more confusing tasks of far larger complexity, which demonstrates that the tasks can be solved in absence of specific evolved 'social contract' modules.

There is an example of non-junk: the evolutionary pressure can adjust strength of pre-existing emotions such as anger, fear, and so on, and even decrease the intelligence whenever the higher intelligence is maladaptive.

Other commonly neglected fact: the evolution is not a watchmaker, blind or not. It does not choose a solution for a problem and then work on this solution! It works on all adaptive mutations simultaneously. Evolution works on all the solutions, and the simpler changes to existing systems are much quicker to evolve. If mutation that tweaks existing system improves fitness, it will, too, be selected for, even if there was a third eye in progress.

As much as it would be more politically correct and 'moderate' for e.g. evolution of religion crowd to get their point across by arguing that the religious people have evolved specific god module which doesn't do anything but make them believe in god, than to imply that they are 'genetically stupid' in some way, the same selective pressure would also make the evolution select for non-god-specific heritable tweaks to learning, and the minor cognitive deficits, that increase religiosity.

Lined slate as a prior

As update for tabula rasa, picture lined writing paper; it provides some guidance for the handwriting; the horizontal lined paper is good for writing text, but not for arithmetic, the five-lines-near-eachother separated by spacing is good for writing music, and the grid paper is pretty universal. Different regions of the brain are tailored to different content; but should not be expected to themselves code different algorithms, save for few exceptions which had long time to evolve, early in vertebrate history.

edit: improved the language some. edit: specific what sort of evolutionary psychology I consider to be junk, and what I do not, albeit that was not the point of the article. The point of the article was to provide you with the notions to use to see what sorts of evolutionary psychology to consider junk, and what do not.