The Nature versus Nurture debate is a long-standing one among biologists and psychologists. Does Nature (our genes) determine what we become, or does Nurture (our environment)? The answer is obviously both, but as this NOVA: "Cracking the Code of Life" Web site explains, recent findings have placed a greater emphasis on Nurture.
10H/H5 ( Grades: 9-12 ): A mechanism that explained the origin of variation within species was suggested by several lines of evidence: findings from Gregor Mendel's experiments on the inheritance of traits in plants, the identification of genes and how they are sorted in reproduction, and the discovery of the mutability and near universality of the genetic code found in DNA.
5A/H1a ( Grades: 9-12 ): The variation of organisms within a species increases the likelihood that at least some members of the species will survive under changed environmental conditions.
5F/H3 ( Grades: 9-12 ): Natural selection provides the following mechanism for evolution: Some variation in heritable characteristics exists within every species; some of these characteristics give individuals an advantage over others in surviving and reproducing; and the advantaged offspring, in turn, are more likely than others to survive and reproduce. As a result, the proportion of individuals that have advantageous characteristics will increase.
5F/H4a ( Grades: 9-12 ): Heritable characteristics can be observed at molecular and whole-organism levels—in structure, chemistry, or behavior.
NSTA National Science Education Standards
C.2.1 ( Grades: 9-12 ): In all organisms, the instructions for specifying the characteristics of the organism are carried in DNA, a large polymer formed from subunits of four kinds (A, G, C, and T). The chemical and structural properties of DNA explain how the genetic information that underlies heredity is both encoded in genes (as a string of molecular "letters") and replicated (by a templating mechanism). Each DNA molecule in a cell forms a single chromosome.
C.2.2 ( Grades: 9-12 ): Most of the cells in a human contain two copies of each of 22 different chromosomes. In addition, there is a pair of chromosomes that determines sex: a female contains two X chromosomes and a male contains one X and one Y chromosome. Transmission of genetic information to offspring occurs through egg and sperm cells that contain only one representative from each chromosome pair. An egg and a sperm unite to form a new individual. The fact that the human body is formed from cells that contain two copies of each chromosome--and therefore two copies of each gene--explains many features of human heredity, such as how variations that are hidden in one generation can be expressed in the next.
C.2.3 ( Grades: 5-8 ): Every organism requires a set of instructions for specifying its traits. Heredity is the passage of these instructions from one generation to another.
C.2.4 ( Grades: 5-8 ): Hereditary information is contained in genes, located in the chromosomes of each cell. Each gene carries a single unit of information. An inherited trait of an individual can be determined by one or by many genes, and a single gene can influence more than one trait. A human cell contains many thousands of different genes.
C.3.1 ( Grades: 9-12 ): Species evolve over time. Evolution is the consequence of the interactions of (1) the potential for a species to increase its numbers, (2) the genetic variability of offspring due to mutation and recombination of genes, (3) a finite supply of the resources required for life, and (4) the ensuing selection by the environment of those offspring better able to survive and leave offspring.
C.5.2 ( Grades: 5-8 ): Biological evolution accounts for the diversity of species developed through gradual processes over many generations. Species acquire many of their unique characteristics through biological adaptation, which involves the selection of naturally occurring variations in populations. Biological adaptations include changes in structures, behaviors, or physiology that enhance survival and reproductive success in a particular environment.