Research methods of Sutton hypothesis in biology

"Hypothetical deduction" and its important role in the development of natural science

Scientific hypothesis is a speculative explanation (or guess, guess) made by people on the basis of certain empirical materials and known scientific facts, under the guidance of existing scientific theories and technical methods, on the causes and motion laws of unknown natural things or phenomena, the existence of unknown things or the image of things expected to be discovered. [1] When people put forward hypotheses, they often use thinking methods and research methods such as analysis and synthesis, induction and deduction and analogy imagination to process the existing empirical materials. For example, Darwin, the founder of the theory of evolution, saw that two islands far apart had the same freshwater swamp plants. He put forward a hypothesis that these freshwater plants can cross the ocean and take root on another island because waterfowl brought their seeds to another island. Later, Darwin tested his hypothesis through experiments.

From the general mode of scientific activities, hypothesis is a necessary link leading to scientific theory. The main task of scientific research and scientific theory is to try to explain the existing experience and facts, and to predict the future experience and facts, and scientific hypothesis is the basic thinking form to realize this kind of trying explanation and prediction.

Hypothesis must be tested by scientific practice before it can develop into a scientific theory. The testability of hypothesis is closely related to the possibility of deductive expansion of hypothesis. Observation and experiment often test not the hypothesis itself, but the inference of the hypothesis, that is, the inference derived from the hypothesis logic to describe individual phenomena or events. For example, Mendel made a cross experiment of a pair of relative characters with peas, and observed the phenomenon of character separation. He put forward the famous particle genetic hypothesis in the history of genetics to explain the reason of character separation. This hypothesis suggests that the relative traits of organisms are determined by the genetic factors of sexual relations; Genetic factors exist in pairs in somatic cells; When an organism forms a gamete, the paired genetic factors are separated from each other and enter different gametes respectively; In the process of fertilization, the combination of male and female gametes is random. Under the conditions at that time, Mendel could not directly prove his hypothesis through microscopic observation, but only relied on experiments (see below).

Deduction is a logical reasoning method from general to individual. Contrary to inductive reasoning, deductive reasoning is a scientific way of thinking and scientific research method to infer new conclusions from some known general principles, theorems, laws, axioms or scientific concepts. [2] that is, set B has some attribute, and A is a member of set B, so A also has this attribute. For example, all living things can metabolize, and bears are also living things, so bears can metabolize.

"Hypothesis-deduction method" is to put forward a hypothesis to explain the problem through reasoning and imagination after asking questions on the basis of observation and analysis, and then make deductive reasoning according to the hypothesis, and then test the conclusion of deductive reasoning through experiments. If the experimental results are consistent with the expected conclusions, it proves that the hypothesis is correct, otherwise, it proves that the hypothesis is wrong. It can be seen that deductive reasoning is a kind of inevitable reasoning, that is, the reasoning process or form that inevitably leads to conclusions from one or several premises. At present, the most popular hypothesis-deduction model can be illustrated as follows: p … h ∝ oc → HC [3]. Its significance is: a study begins with solving a problem (P), and deduces a hypothesis (H) through logical reasoning or imagination (……), from which it deduces (∝) inevitable observable statements (OC) to be tested, and if these statements are proved to be correct, it draws (→) a definite conclusion (HC).

Hypothetical deduction is a common scientific method in modern scientific research. "Hypothesis-deduction method" is regarded as an ideal method to construct scientific theory, and is also regarded by some people as the basic mode of scientific knowledge growth. Newton's process of establishing the color theory of light is an example of applying the "hypothesis-deduction method". The process of putting forward and verifying Einstein's general theory of relativity and the cyclic structure of benzene molecule put forward by Kekule are typical cases of "hypothesis-deduction method". In the development of genetics, there are many "hypothesis-deduction" cases.

Materials that can be used for "hypothesis-deduction" teaching in the module of heredity and evolution.

/kloc-before the 0/9th century, scientists used to accumulate empirical materials through experiments and observations, sum them up and generalize them, and finally abstract a theory or doctrine, that is, induction. "Hypothesis-deduction method" is a science that finds problems from the analysis of objective phenomena or experimental results, puts forward assumptions, and then designs experiments to verify the assumptions. This method enables the research results of genetics to surpass the development of science at that time, promotes new scientific discoveries, and enables genetics to enter rational deduction and experimental verification from descriptive science. Hypothesis-deduction has played an important role in the development of genetics. Therefore, teachers should make full use of the relevant materials of genetics to educate students on "hypothesis-deduction" in order to improve their biological science literacy. Here are some important materials for teachers' reference.

Hybrid experiment of pea and material 1 Mendel. /kloc-In the middle of the 9th century, Mendel did a lot of hybridization experiments with peas. In the process of observing, recording and analyzing the experimental results, it was found that a certain proportion of traits were separated from the hybrid offspring, and the second generation appeared the phenomenon of free combination of different traits in two or more pairs of relative traits hybridization experiments. He put forward a hypothesis through rigorous reasoning and bold imagination, trying to explain the phenomenon of personality separation and free combination of different characters. Then he cleverly designed a cross-test experiment to test the hypothesis. It is impossible to directly verify the hypothesis itself, but to verify the inference derived from the hypothesis, that is, if the hypothesis that genetic factors determine biological characteristics is established, then the results of the test experiment can be deduced and predicted theoretically according to the hypothesis; Then, the experimental data are compared with the theoretical derivation. If they are consistent, the assumption is correct; If they don't agree, the assumption is wrong. Of course, the actual test process of hypothesis is very complicated, and it is impossible to explain the problem by one or two experiments alone. In fact, many experiments conducted by Mendel have obtained similar results. Later, several scientists made many observations similar to Mendel's experiment. After a large number of experiments verified the authenticity of Mendel hypothesis, Mendel hypothesis finally developed into a classic theory of genetics. As we know, deductive reasoning is an important form of reasoning in scientific argumentation. Why can the consistency between experimental values and theoretical deduction prove the correctness of the hypothesis? Facts have proved that the phenotype and proportion of the offspring of test cross truly reflect the type and proportion of gametes produced by the offspring. According to the gamete type of offspring, its genetic composition can be inferred, and revealing this mystery will play a finishing role in the process of deductive reasoning. Without revealing this mystery, it will be difficult for students to understand the scientific and rigorous nature of the "hypothesis-deduction method", and the conclusion drawn by deductive reasoning will remain in a state of ignorance.

Material 2 1900, three scientists rediscovered Mendel's work respectively, and the genetic circle began to realize the significance of Mendel's genetic theory. If Mendel's supposed genetic factor, the gene, does exist, then where is it? 1903, American geneticist Sutton found that the segregation of a pair of genetic factors, namely alleles, assumed by Mendel was very similar to the segregation of homologous chromosomes in meiosis. According to the obvious parallel relationship between genes and chromosome behavior, Sutton put forward the hypothesis that genes are carried from parents to offspring by chromosomes, that is, genes are located on chromosomes. Morgan, an American geneticist, made it clear that he did not believe Mendel's genetic theory and doubted Sutton's hypothesis. Later, he did a lot of fruit fly hybridization experiments to connect a specific gene with a specific chromosome-X chromosome, thus confirming Sutton's hypothesis. It can be seen that the process of exploring the relationship between genes and chromosomes is also a hypothetical-deductive process.

Material 3 The presentation and confirmation of DNA molecular structure and replication mode, as well as the presentation and confirmation of the whole central rule, are all cases of "hypothesis-deduction method". Take the clarification of DNA molecular replication mode as an example. Watson, an American biologist, and Crick, a British physicist, wrote at the end of their famous paper on the double helix structure of DNA molecules: "After putting forward the viewpoint of base-specific pairing, we immediately put forward a possible mechanism of genetic material replication." They immediately published the second paper and put forward the hypothesis that genetic material replicates itself: when DNA molecules replicate, the double helix is untied, and the untied two single strands are used as templates to form new strands according to the principle of base complementary pairing, so each new DNA molecule retains one strand of the original DNA molecule. This method of replication is called semiconservative replication. 1958, scientists used Escherichia coli as experimental materials and designed ingenious experiments by isotope labeling. The experimental results are consistent with the expected phenomenon deduced from the hypothesis, which confirms that DNA does replicate in a semi-reserved way.

The decoding of genetic code is another important event in the development of modern genetics after the model of DNA double helix structure was put forward. Since 1953 put forward the model of DNA double helix structure, scientists have made a series of explorations around the decoding of genetic code. The idea that three bases encode 1 amino acid was put forward by American Soviet physicist Gamov. Crick and his colleagues studied the effect of base increase or decrease of a gene on protein encoded by T4 phage through a large number of experiments. The results showed that only three bases in the genetic code could encode 1 amino acid. But their experiments can't explain which amino acid the 1 code of the three bases corresponds to. Nirenberg and Matthew, two young American biologists, changed their design ideas and skillfully designed experiments, which successfully cracked the first genetic code. In the following six or seven years, scientists deciphered all the genetic codes and compiled a codon table.

From the above materials, we can see that "hypothesis-deduction method" is not only an important method in classical genetics research, but also plays a very important role in the development of modern genetics. Because of this, it is very correct for senior high school biology curriculum standards to require students to understand the "hypothesis-deduction method" in the "heredity and evolution" module of Biology II. Therefore, in teaching, we should not only guide students to acquire knowledge and skills, but also guide students to experience the process of knowledge formation, understand the thinking mode of scientists and strengthen the training of scientific methods.