Allan C. Wilson studied genes, proteins, and body structures of animals and humans in the US during the second half of the twentieth century. Wilson also studied human evolution. Although morphology and behaviors of humans (Homo sapiens) and great apes differ, Wilson found that they have biochemical and genetic similarities. Wilson and his colleagues calculated the time period of humans' and African apes' common ancestor. Wilson and his team also studied DNA outside of the nucleus in the cellular energy producing particles, called mitochondrial DNA (mtDNA), to study when different human groups evolved from each other.

Advanced Cell Technology (ACT), a stem cell biotechnology company in Worcester, Massachusetts, showed the potential for cloning to contribute to conservation efforts. In 2000 ACT researchers in the United States cloned a gaur (Bos gaurus), an Asian ox with a then declining wild population. The researchers used cryopreserved gaur skin cells combined with an embryo of a domestic cow (Bos taurus). A domestic cow also served as the surrogate for the developing gaur clone. The successful procedure opened the opportunity to clone individuals from species for which there are few or zero live specimens. The official release of this experiment's data was published in the paper 'Cloning of an Endangered Species (Bos gaurus) Using Interspecies Nuclear Transfer,' in October 2000. In the article, the researchers presented data collected from several cloned fetuses that were aborted before the full term of 283 days. At the time of publication, the gaur bull fetus, named Noah at birth, had developed for greater than 180 days. Noah was born on 8 January 2001, but died two days later due to dysentery. The development, birth, and death of Noah became a platform for conservationists and ethicists to critique the role of cloning in society and as a method to conserve species.

In 1987 Rebecca Louise Cann, Mark Stoneking, and Allan Charles Wilson published Mitochondrial DNA and Human Evolution in the journal Nature. The authors compared mitochondrial DNA from different human populations worldwide, and from those comparisons they argued that all human populations had a common ancestor in Africa around 200,000 years ago. Mitochondria DNA (mtDNA) is a small circular genome found in the subcellular organelles, called mitochondria. Mitochondria are organelles found outside of the nucleus in the watery part of the cell, called cytoplasm, of most complex cells (eukaryotes). Cann, Stoneking and Wilson collected mtDNA from 147 individuals from five different human geographical populations. Cann, Stoneking, and Wilson used mtDNA sequences to study the genetic differences and migration patterns of the human population through female inheritance. Mammals inherit mitochondria and mtDNA from their mothers through the egg cell (oocyte), and mitochondria are responsible for several maternally inherited diseases.

Mitochondrial DNA (mtDNA) is located outside the nucleus in the liquid portion of the cell (cytoplasm) inside cellular organelles called Mitochondria. Mitochondria are located in all complex or eukaryotic cells, including plant, animal, fungi, and single celled protists, which contain their own mtDNA genome. In animals with a backbone, or vertebrates, mtDNA is a double stranded, circular molecule that forms a circular genome, which ranges in size from sixteen to eighteen kilo-base pairs, depending on species. Each mitochondrion in a cell can have multiple copies of the mtDNA genome. In humans, the mature egg cell, or oocyte, contains the highest number of mitochondria among human cells, ranging from 100,000 to 600,000 mitochondria per cell, but each mitochondrion contains only one copy of mtDNA. In human embryonic development, the number of mitochondria, the content of mtDNA in each mitochondrion, and the subsequent mtDNA activity affects the production of the oocytes, fertilization of the oocytes, and early embryonic growth and development.

All cells that have a nucleus, including plant, animal, fungal cells, and most single-celled protists, also have mitochondria. Mitochondria are particles called organelles found outside the nucleus in a cell's cytoplasm. The main function of mitochondria is to supply energy to the cell, and therefore to the organism. The theory for how mitochondria evolved, proposed by Lynn Margulis in the twentieth century, is that they were once free-living organisms. Around two billion years ago, mitochondria took up residence inside larger cells, in a process called endosymbiosis, becoming functional parts of those cells. Within each mitochondrion is the mitochondrial DNA (mtDNA), which is different from the DNA in the cell's nucleus (nDNA). Organisms inherit their mitochondria only from their mothers via egg cells (oocytes). Mitochondria contribute to the development of oocytes, the release of the oocyte from the ovary (ovulation), the union of oocyte and sperm (fertilization), all stages of embryo formation (embryogenesis), and growth of the embryo after fertilization.