Darwin knew nothing of genes. He was unaware of the work of Gregor Mendel, the Austrian monk who worked in his monastery garden and did experiments on the inheritance of pod-color in peas. Mendel discovered that heritable traits such as pod-color are inherited in discrete packages which he called genes. Any act of sexual reproduction of two parents with different genes results in offspring with a random distribution of the parental genes. Heredity in any population is a random process, resulting in a redistribution of genes between parents and offspring. The numbers of genes of various types are maintained on the average from generation to generation, but the numbers in each individual offspring are random. Mendel made this discovery and published it in the journal of the Brünn Natural History Society, only seven years after Darwin published The Origin of Species. Mendel had read Darwin's book, but Darwin never read Mendel's paper. In 1866, the year when Mendel's paper was published, Darwin did a very similar experiment, using snap-dragons instead of peas, and testing the inheritance of flower-shape instead of pod-color. Like Mendel, he bred three generations of plants, and observed the ratio of normal-shaped to star-shaped flowers in the third generation. Unlike Mendel, he had no understanding of the mathematics of statistical variations. He used only 125 third-generation plants and obtained a value of 2.4 for the ratio of normal to star-shaped offspring. This result did not suggest any clear picture of the way flower-shapes are inherited. He stopped the experiment and explored the question no further. Darwin did not understand that he would need a much larger sample to obtain a statistically significant result. Mendel understood statistics. His sample was sixty-four times larger than Darwin's, so that his statistical uncertainty was eight times smaller. He used 8023 plants. Mendel's essential insight was to see that sexual reproduction is a system for introducing randomness into inheritance. In peas as in humans, inheritance is carried by genes that are handed down from parents to offspring. His simple theory of inheritance carried by genes predicted a ratio of three between green and yellow pods in the third generation. He found a ratio of 3.01 with the big sample. This gave him confidence that the theory was correct. His experiment required immense patience, continuing for eight years with meticulous attention to detail. Every plant was carefully isolated to prevent any intruding bee from causing an unintended fertilization. A monastery garden was an ideal place for such experiments. Unfortunately, his experiments ended when his monastic order promoted him to the rank of abbot. Obedient to his vows, he ceased to be an explorer and became an administrator. His life-work lay hidden in an obscure German-language journal in Brünn, the city that later became Brno and is now in the Czech Republic.

the neo-Darwinists were practically driven to their conclusions by their initial assumption: that science demands a rational explanation, that this means attributing rational motives to all behavior, and that a truly rational motivation can only be one that, if observed in humans, would normally be described as selfishness or greed.

In other words, the palette of social organization was rich and diverse from the beginning: early humans, like us, were constantly in the business of shaping and reshaping their social arrangements, with evidence of conscious embracing and rejection of all sorts of social forms.

trait

Tumor suppressor genes

Th ough cautions are oft en expressed [e.g., Plomin, DeFries, McClearn, & Rutter, 1997], the fact that reported biological mothers-adopted children correlations are higher than adoptive mothers-adopted children correlations has had a big impact in psychology and on theories of development. Most usually, the correlations have been computed into heritability