Bringing Extinct Species Back to Life | Dr. Beth Shapiro

Beth Shapiro frames de-extinction as one branch of a wider conservation effort. Colossal’s dire wolves were made by selecting genetic edits from fossil genomes and engineering those changes into a gray wolf genome. Her answer to the question of why this work should take priority over preventing extinctions is that the same tools, technology, and needs serve both goals. Public interest in mammoths, dodos, and thylacines, she argues, can also attract engagement and investment in tools used to protect living species. The claim is therefore not that reviving extinct animals replaces conservation, but that the projects share a technical base and may reinforce one another through attention and resources.

The host places this debate in the context of Shapiro’s evolutionary biology work at Colossal and the company’s projects involving woolly mammoths, dodos, and dire wolves. He connects those projects to broader questions about species preservation, genomics, human genetic engineering, and ethics. The introduction also sets a boundary around the episode’s claims: dinosaurs are not part of the plan, and the discussion will explain why. This framing presents de-extinction as both a specific program of genetic engineering and an entry point into questions about how people classify and alter living things.

Shapiro’s starting point for the species question is that “species” is a human category rather than a boundary that biology itself needs to recognize. People group organisms so they can name them, discuss them, and share stories and memories; language makes those categories useful for communication and social life. The host links this to the familiar taxonomic ladder and Linnaeus’s system. The distinction matters because a naming scheme helps people organize evolutionary relationships, while the organisms and their histories do not necessarily fall into perfectly discrete boxes.

The bison example shows how common names can blur biological distinctions. Shapiro says American bison are often called buffalo, and that African, Asian, and American buffalo share a name despite being unrelated according to DNA. In her account, the shared label arose from a practical resemblance people associated with useful hides, while taxonomists wanted names that made clear which animal was meant. Linnaeus’s naming scheme is offered as a response to that ambiguity: it gives the American plains bison a repeated Latin name across genus, species, and subspecies. The episode uses the repetition for humor, but the underlying point is that everyday names and scientific classification answer different needs.

The host then distinguishes taxonomy from a species concept: taxonomy organizes organisms within evolutionary history, while a species concept is a test people use to decide whether two animals belong to the same species. The biological species concept associated here with Ernst Mayr uses reproduction as its criterion: if two organisms can breed and produce fertile offspring, they count as the same species. The host calls this a good starting point and offers fruit flies as an example of a reproductive barrier between species. The exchange treats the criterion as a practical introduction, rather than claiming that one definition resolves every difficult case in classification.

The conversation tests species boundaries against ordinary breeding behavior before turning to formal definitions. Shapiro describes the biological species concept as one useful criterion: organisms that can interbreed and produce fertile offspring are treated as the same species. She contrasts this with a genetic species concept, which sorts organisms by a threshold of sequence similarity, and a geographic concept that may name populations differently according to where they live. Her central qualification is that biology does not choose among these concepts; people adopt them to answer particular questions. The dog examples make the issue conversational, but do not establish a general biological rule about cross-species mating.

Neanderthals and Denisovans show why the reproductive definition can become complicated. Shapiro recounts evidence that anatomically modern humans encountered and interbred with Neanderthals after migrating out of Africa, and that DNA studies also identify Denisovans from remains found in Denisova Cave. If Neanderthals were a distinct species, their interbreeding with Homo sapiens would not fit a strict reading of the biological species concept. The interview reports that many people today carry roughly 2–5% Neanderthal ancestry from this admixture. Rather than treating the label as a hierarchy, the discussion uses the case to show that lineage, ancestry, and species names do not always line up neatly.

The exchange contrasts the patchiness of the human fossil record with the added evidence ancient DNA can provide. A partial jaw or tooth may prompt major revisions to evolutionary history, but the interpretation remains contested because so few bones are available. DNA recovered from a small finger bone in Denisova can identify the lineage more directly and can be compared with DNA from people alive today. Shapiro also distinguishes ancestry from descendants: a fossil may belong to a lineage ancestral to living humans, or to a branch that left no living descendants and later became extinct. Sequencing helps place remains among these possibilities and reveals interbreeding between lineages, while the speakers present that evidence as one reason the species boundaries are not simple.

The speakers treat the origin of species as a long, context-dependent process rather than a sudden jump. Shapiro says random mutations accumulate in genomes, while populations separated in different habitats experience different selective pressures. Population size also matters: in a small population, even harmful mutations can become fixed by chance. Over time, these changes can make lineages increasingly distinct, but whether they can interbreed after meeting again depends on which changes arose. Some barriers may appear quickly, such as incompatibility between sperm and egg or problems in hybrid development; in other cases, substantial time can pass without preventing admixture. Shapiro calls this an open question in evolutionary biology.

Polar and brown bears provide the episode’s concrete example of long-separated lineages that still interbreed. The speakers describe the two groups as having diverged roughly half a million years ago, yet being able to mate when their habitats overlap. Ancient DNA from an old polar bear showed ancestry also found in brown bears, and Shapiro describes later contact when brown bears expanded onto the ABC Islands in southeast Alaska during the last ice age. She says that brown bears alive in North America today carry polar-bear ancestry from that interbreeding. The example shows that divergence time alone does not determine reproductive isolation.

The bear example also shows that hybridization is not necessarily symmetrical or equally successful in both lineages. Shapiro says the detected ancestry appears in brown bears rather than polar bears, and relates this to differences in reproductive timing and ecology: polar bears are induced ovulators, while a brown bear male encountering a polar bear female could trigger ovulation. She recounts a hypothesis from polar-bear biologists that brown-bear ancestry would compromise the white coat needed to hunt seals, so hybrids could be born but fail to survive as polar bears. The distinction is between reproductive compatibility and the later ability of an animal to live in a particular habitat.

The host then uses dog breeding to explore how reproductive barriers can be shaped by human choices, describing bulldog traits and the difficulty of birth when puppy head and maternal pelvis dimensions do not fit. He extends this into an explicitly imaginative question about whether other human lineages could have produced pregnancies that did not survive because of pelvic and head-size differences. This remains a speculative analogy in the conversation, not evidence about human evolution. Its role is to separate the ability to conceive or produce a hybrid from the further conditions required for offspring to be born and survive.