In contemporary psychology, this question of whether anything emerges from "nature" - or - "nurture" is largely gone. Psychologists now recognize that many, if not most, psychological phenomena emerge from complex interactions between natural, biological forces and environmental factors (nurture).

For example, it's well-known that the probability a person will develop schizophrenia is linked to their mother having contracted influenza during a particular time-period during pregnancy. Mood disorders also seem to have some sort of biological link based on twin and family studies (which are by no means perfect from a research design and theory perspective, but the evidence is at least fairly consistent).

Even things that seem decisively basic - like brain structure - are not strictly determined by biology/genetics. For example, Sharma, Angelucci, and Sur (2000) demonstrated that the brain's auditory cortex will "rewire" to process visual signals if the visual pathway is re-routed so the visual signals are sent to the auditory processing areas of the brain. See their study on ferrets - "Induction of visual orientation modules in auditory cortex" (journal = Nature).

When it comes to nature/nurture in abnormal psychology, there are few psychological illnesses that are 100% tied to genes or environment. Children raised in very abusive homes by parents who have severe psychological illness can grow-up to be quite normal and well-adjusted. Likewise, children born to normal, caring parents can grow-up to develop severe psychological problems. There are many complex interacting factors that give rise to psychological illness (and anything else in psychology, e.g. personality).

To me, some of the best accounts of nature-nurture in modern psychology come from the ideas of "experiential canalization" and "epigenesis." The basic idea behind epigensis is that any organism's development is a product of multiple interactions between genes, protein structures, environment, and behavior (response and feedback) within the environment over time. Accordingly, genes can influence behavior - but behavior can also influence genes (e.g. if a person does not secure adequate food, then that person's biological health and subsequent cell development can suffer).

The idea behind experiential canalization is that the range of options an organism has for development and growth will be linked to past experience and events. For example, a person who spends childhood in an impoverished environment with exposure to environmental toxins may go on to have higher risk for cancer and a subsequent shorter lifespan.

To learn more about these two ideas see:

Gottlieb (1991) "Experiential Canalization of Behavioral Development: Theory" (Journal = Developmental Psychology)

Bjorklund, D. f. (2006). "Mother knows best:Epigenetic inheritance, maternal effects, and the evolution of human intelligence." (Journal = Developmental Review)

The  "Nature-nurture" problem seems to still be a research topic of interest:

Mandated reporting: The effects of self-care and professional help seeking behavior on mental health care providers' levels of distress. Croft, Megan Anne. The Chicago School of Professional Psychology, ProQuest, UMI Dissertations Publishing, 2015. 3619520.

Continuity of genetic and environmental influences on cognition across the life span: A meta-analysis of longitudinal twin and adoption studies. Tucker-Drob, Elliot M.; Briley, Daniel A.. Psychological Bulletin 140.4 (Jul 2014): 949-979.

Accounting for genetic and environmental confounds in associations between parent and child characteristics: A systematic review of children-of-twins studies. McAdams, Tom A.; Neiderhiser, Jenae M.; Rijsdijk, Fruhling V.; Narusyte, Jurgita; Lichtenstein, Paul; et al. Psychological Bulletin 140.4 (Jul 2014): 1138-1173.

Friendship conflict and the development of generalized physical aggression in the early school years: A genetically informed study of potential moderators. Salvas, Marie-Claude; Vitaro, Frank; Brendgen, Mara; Dionne, Ginette; Tremblay, Richard E.; et al. Developmental Psychology 50.6 (Jun 2014): 1794-1807.

Friends or foes: Infants use shared evaluations to infer others’ social relationships. Liberman, Zoe; Kinzler, Katherine D.; Woodward, Amanda L.. Journal of Experimental Psychology: General 143.3 (Jun 2014): 966-971.

What determines happiness? Income or attitude: Evidence from the U.S. longitudinal data. Mohanty, Madhu S.. Journal of Neuroscience, Psychology, and Economics 7.2 (Jun 2014): 80-102.

Early adverse environments and genetic influences on age at first sex: Evidence for gene × environment interaction. Carlson, Marie D.; Mendle, Jane; Harden, K. Paige. Developmental Psychology 50.5 (May 2014): 1532-1542.

Mind the gap: Why many geneticists and psychological scientists have discrepant views about gene–environment interaction (G×E) research. Duncan, Laramie E.; Pollastri, Alisha R.; Smoller, Jordan W.. American Psychologist 69.3 (Apr 2014): 249-268.

I understand the biolohical & psychological aspects of nature vs nurture but my other question I want to ask is.

Can to much of one or the other or both can be harmful to a childs cognitive learning or how they start to make rational decIsIon making?

No but too little education can be harmful

Hi Angela,

In developmental psychology, environmental richness is one factor known to influence a child's cognitive abilities. During infancy and very early childhood, children who are exposed to a wide array of stimuli tend to develop stronger cognitive abilities. One strong illustration of this is recent findings that children who are raised in lower income households tend to have a significantly poorer vocabulary later in childhood relative to children raised in higher income households. This clearly illustrates strong environmental influence on cognitive development.

That said, biology plays a key role in various ways. For example, autism is linked to biological factors. If a child has autism, environmental factors may not be able to fully overcome this disorder. That said, the earlier a child is diagnosed with autism and the more intensive the intervention at an early age, the better the later outcomes.

Much of what happens with childhood development is linked to the complex interaction between nature and nurture. During early childhood, and infancy, the brain undergoes substantial changes, especially with respect to neural connectivity. Therefore, children who are exposed to a wider array of stimuli benefit from their rapid neural development. Nature and nurture are inexorably linked when it comes to development.