From 1951 to 2001, researchers at the University of Oxford in Oxford, England, conducted the British Doctors’ Study, a study that examined the smoking habits, disease rates, and mortality rates of physicians in Britain. Two epidemiologists, scientists who study occurrence and distribution of disease, Richard Doll and Austin Bradford Hill, initiated the study, and statistician Richard Peto joined the team in 1971. The objective of the study was to assess the risks associated with tobacco use, and its relationship to lung cancer. The researchers tracked 34,439 male doctors practicing in Britain, and recorded smoking habits, development of diseases including lung cancer, other cancers, respiratory diseases, cardiovascular diseases, and mortality rates. The researchers published updated results every ten years. In 1980, Doll and other researchers concluded a related study on the smoking habits and disease rates of female doctors practicing in Britain. The results of both studies provided evidence that individuals who smoked tobacco were more likely to develop chronic respiratory illnesses, including lung cancer, and cardiovascular diseases.

"A Diffusible Agent of Mouse Sarcoma, Producing Hyperplasia of Sympathetic Ganglia and Hyperneurotization of Viscera in the Chick Embryo," by Rita Levi-Montalcini and Viktor Hamburger, appeared in 1953 in the Journal of Experimental Zoology. The paper provided the first evidence that nerve growth factor is a diffusible substance. Nerve growth promoting tumors were implanted into developing embryos to determine whether the tumors stimulated growth by direct contact or by a diffusible substance. The tumors were implanted into different parts of the embryo; one set of experiments implanted the tumor directly in the embryo, while another set of experiments placed the tumor on an exterior membrane. The membrane provided a barrier to direct contact with the nervous system, and allowed some chemical interaction between the tumor and the embryo. The tumor stimulated growth in both orientations, demonstrating that nerve growth factor was a chemical agent. The paper ends with two possible conclusions for the mechanism of nerve growth, the tumor may have been directly stimulating the ganglia by a diffusible signal, or it may have reduced the resistance of the chick tissues to the nerve growth. The term "nerve growth factor" is not explicitly used in this paper, and is referred to as a "diffusible agent" or a "growth promoting agent."

Alejandro Sánchez Alvarado's laboratory group has employed molecular tools to investigate old questions about regeneration and as a result have identified some of the molecular mechanisms determining polarity. Recent work by his group has shown Wnt-β-catenin signaling determines whether a tail or a head will form during regeneration in planarians. This study was motivated by work Thomas Hunt Morgan conducted in the late nineteenth century. Morgan observed that during regeneration a planarian cut into rather small pieces would sometimes regenerate a head at both its anterior and posterior end rather than a head and a tail. This led Morgan to think the size of the piece must affect the regenerative process.

On 10 March 1988, China's first baby conceived through human in vitro fertilization (IVF) and embryo transfer (ET), commonly referred to as a test-tube baby, was born at the Peking Hospital (PUTH) in Beijing. This birth was reported in numerous media reports as a huge step forward in China's long march to keep pace with global advances in science and technology. Led by gynecologist Zhang Lizhu, the PUTH research team had devoted more than four years to the human IVF-ET project. The team had to start by learning the basics of human egg morphology and embryology in order to design an IVF-ET strategy that was suited to the reproductive pathology affecting China's infertile population.

Dr. John Rock, a doctor of obstetrics and gynecology in Boston, and Miriam Menkin, Rock s hired lab technician, were the first researchers to fertilize a human egg outside of a human body in February of 1944. Their work was published on 4 August 1944 in an issue of Science in an article entitled "In Vitro Fertilization and Cleavage of Human Ovarian Eggs." This experiment marked the first time in history that a human embryo was produced outside of the human body, proving that in vitro fertilization was possible in humans. The initial approach in the research was to see if experiments involving the fertilization of egg cells in rabbits and rats could be repeated with human egg cells. Based on previous experiments with other mammals, Rock and Menkin believed that the same could be done with human egg cells.

In the early 2000s, Richard S. Legro, Mark V. Sauer, Gilbert L. Mottla, Kevin S. Richter, William C. Dodson, and Duanping Liao studied the relationship between air pollution and reproductive complications. In the United States, Legro’s team tracked thousands of women undergoing in vitro fertilization, or IVF, along with the air quality of both the IVF clinics and patients’ home locations. IVF is a reproductive technology during which a physician obtains mature eggs from a patient’s ovaries and fertilizes them with sperm in a lab setting outside of the body, after which the physician transfers the fertilized eggs into the patient’s uterus. As stated in Legro’s publication, Legro suspected that poor air quality would adversely affect live birth rates during IVF, so he compiled and analyzed the various types of pollutants that IVF patients were naturally exposed to in their homes and clinics. Legro’s experiment led to an increased awareness among patients about the dangers of conceiving via IVF in highly polluted areas.

The biomedical accomplishment of human in vitro fertilization and embryo transfer (IVF-ET) took years to become the successful technique that presently enables infertile couples to have their own children. In 1969, more than ten years after the first attempts to treat infertilities with IVF technologies, the British developmental biologist Robert Geoffrey Edwards fertilized human oocytes in a Petri dish for the first time. In 1970, Edwards and his research partner, gynecologist and surgeon Patrick Christopher Steptoe, started working with human patients with complicated and individualized gynecological conditions. It took Edwards and Steptoe another eight years of modifying medical procedures, as well as dealing with the ups and downs of funding situations and public opinions, before they could celebrate birth of the first baby conceived through IVF-ET in 1978.

Robert Geoffrey Edwards, a British developmental biologist at University of Cambridge, began exploring human in vitro fertilization (IVF) as a way to treat infertility in 1960. After successfully overcoming the problem of making mammalian oocytes mature in vitro in 1965, Edwards began to experiment with fertilizing matured eggs in vitro. Collaborating with other researchers, Edwards eventually fertilized a human egg in vitro in 1969. This was a huge step towards establishing human IVF as a viable fertility treatment. During the four years in which Edwards experimented with IVF, he experienced many setbacks. These failures in fertilizing oocytes in vitro, however, contributed to the understanding of how fertilization did or did not happen, which was sometimes different from established dogmas. Edwards also collaborated with gynecologist and surgeon Patrick Christopher Steptoe to study sperm capacitation, which became the overture that heralded a series of successes for the team, culminating in the generation of the first test-tube baby Louise Joy Brown in 1978.

As mice embryos develop, they undergo a stage of development called gastrulation. The hallmark of vertebrate gastrulation is the reorganization of the inner cell mass (ICM) into the three germ layers: ectoderm, mesoderm, and endoderm. Mammalian embryogenesis occurs within organisms; therefore, gastrulation was originally described in species with easily observable embryos. For example, the African clawed frog (Xenopus laevis) is the most widely used organism to study gastrulation because the large embryos develop inside a translucent membrane. Domestic chicken (Gallus gallus) gastrulation was also an early model organism because researchers could open the egg during development to look inside. Despite the challenges associated with studying mammalian gastrulation, the common house mouse (Mus musculus) has helped to shed light on the unique adaptations associated with mammalian development, and on the subtle differences in structure that give rise to significant divergence in late embryogenesis.

In an effort to develop tissue culture techniques for long-term tissue cultivation, French surgeon and biologist Alexis Carrel, and his associates, produced and maintained a series of chick heart tissue cultures at the Rockefeller Institute in New York City. From 1912 to 1946, this series of chick heart tissue cultures remained alive and dividing. Since the duration of this culture greatly exceeded the normal chick life span, the cells were deemed immortal. Although this conclusion was challenged by further experiments in the 1960s, the publicity surrounding the immortal chick heart tissue significantly influenced the concept of cell immortality and cellular aging from the 1920s through the 1960s. Carrel's experiment convinced many biologists to accept immortality as an intrinsic property of all cells, not just the cell line through which genetic material is passed to offspring, called the germ line. Consequently, the phenomenon of cellular aging was regarded not as an intrinsic characteristic, but was attributed to external factors such as the accumulation of waste products within the cell.