The point about genetic relience is an important one (see Jim B.). In early developmental neuroscience, there was a widely accepted myth that invertebrates (e.g. insects) are "predetermined"/"preformed" creatures, whereas mammals (especially humans) are freely open to developmental sculpturing. The story has now changed in two significant ways.
1) Invertebrate nervous system development is MUCH more plastic, more subject to environmental influences, than previously thought. Genes set the stage; experiences fill in the details. G. Edelman, among many others, have written much about this.
2) Human nervous systems, including their organization in the complexities of language, have strong genetic constraints. This is a derivative from the early insights of Chomsky (and others) on the human mind containing a "language organ" that develops more or less as do hearts and lungs.
I have recently been involved in a review of this material. By chance, as I took a break, I just heard a CBC talk show on human language faculty for people who are deaf and thus use sign language. It appears that many of the same (resilient) parts of the brain normally involved in verbal communication are now involved in sign language. The point is that these parts of the brain are resilient in their language capacity, and plastic in dealing with the modality used in language. The lower-order building blocks are shuffled, but the superstructure remains.
The two obvious lessons are that a) developmental resilience can be found to an often remarkable degree in even the highest forms of human expression, and b) this resilence may follow channels not intuitively obvious (e.g. "fixed" for language; "plastic" for modality).
I suspect that the nature versus nurture issue remains conflicted not just because of the temptation to use dichotomous thought, but also because we do not have a good handle on where to look, and what to expect when we look. Who would have thought that certain properties of invertebrate nervous systems are so sensitive to environmental perturbations? Who would have expected a human brain region relient for higher-order language processing while plastic for modality?
Constraints and plasticities are partners in ways we simply do not grasp. Perhaps the best thing is to look for striking cases of each. Then we can begin to weave a story of how these two conceptual extremes work together in the must more interesting, and much larger, intermediate zone.
We can thus cheer for genes and also cheer for experience. Cheering for one does not negate the other.
I suspect that humans are tightly constrained in many of our so-called higher mental/behavioral functions. We may also be more plastic in processing that we have previously viewed as "fixed".
Higher order brain/behavior functions are almost always the indirect product of numerous genes, and thus gene products. As J.B. suggests, if complex systems employ redundancy to preserve essential functions then resilence and buffers are to be expected.
Since humans are defined (define themselves) as special due to our "higher-order" mental processes, it is not possible to be fully human when these processes go goofy. So perhaps one of the big surprises for the future will be that some of our "higher" mental capacities prove to be as, or even more, resilient to perturbations in development as are those processes that we have traditionally viewed as "lower order".
Part of this may be how we have thought about hierarchies in brain and behavior. The simple (and I suspect incorrect) view is that higher-order capacities result from the mere assembly of many lower-order properties. In that case, errors at any lower-order focus might be expected to disrupt any hopes for higher-order integrity. An alternative view is that what we call "higher-order" has a developmental path that is in some ways independent of its "lower-order" constituents. They form "on their own", so to speak. Since these "higher-order" (e.g. linguistic, symbolic) properties are both complex and vital to human life, they might, surprisingly, have a resilience that remains imperfectly probed.
Of course surprises are what we seek. They educate us. Evolutionary psychology is offering many surprises. Some are hard to pin down, but the social sciences can never again follow their historical negation of biological fact.