During the twentieth and twenty-first centuries, Robert Paul Lanza studied embryonic stem cells, tissues, and endangered species as chief scientific officer of Advanced Cell Technology, Incorporated in Worcester, Massachusetts. Lanza's team cloned the endangered species of gaur Bos gaurus. Although the gaur did not survive long, Lanza successfully cloned another cow-like creature, called the banteng (Bos javanicus). Lanza also worked on cloning human embryos to harvest stem cells, which could be used to treat dieases. While previous techniques required the embryo's destruction, Lanza developed a harvesting technique that does not destroy the embryo, forestalling many ethical objections to human embryonic research.

The Southern Gastric-Brooding Frog (Rheobatrachus silus) was an aquatic frog that lived in south-east Australia. In 2002, the International Union for Conservation of Nature Red List declared the frog extinct, although no wild specimens had been reported since 1981. As the common name alludes to, the R. silus was a gastric-brooder, meaning that the female's eggs developed inside of her stomach. Weeks after ingestion, juvenile frogs escape through the mother's mouth. Because no other observed species performs this reproductive behavior, in the early twenty-first century R. silus became a target of the de-extinction movement that aims to resurrect extinct species. Researchers studied this frog's reproductive behavior and how the eggs and embryos escape digestion. Some scientists claimed that resurrecting this frog could result in future medical applications related to digestion and to reprogramming organ function, as during pregnancy, R. silus's stomach physiologically functioned as a uterus.

George McDonald Church studied DNA from living and from extinct species in the US during the twentieth and twenty-first centuries. Church helped to develop and refine techniques with which to describe the complete sequence of all the DNA nucleotides in an organism's genome, techniques such as multiplex sequencing, polony sequencing, and nanopore sequencing. Church also contributed to the Human Genome Project, and in 2005 he helped start a company, the Personal Genome Project. Church proposed to use DNA from extinct species to clone and breed new organisms from those species.