De-extinction: what the biology allows

A species is not a list of genes, and that single fact organises everything de-extinction can and cannot do. The workflow — read the extinct genome, edit a living relative, gestate the embryo in a surrogate — is real at every step, and each step loses information.

What ancient DNA can and cannot give#

After death, DNA is attacked by water and by microbes: cytosine deaminates, which reads as a C-to-T substitution, and the strands break into short fragments — tens of bases in anything warm; permafrost and caves preserve longest. Recovered genomes are therefore low-coverage mosaics assembled against the reference genome of a living relative, so whatever diverged — repetitive regions, regulatory sequence, unrepresented loci — is either invisible or silently inferred. Comparison with the surrogate yields candidate trait loci, not a complete specification: partly the extinct genome is a reconstruction whose gaps were filled with the nearest living relative’s pieces.

Editing a proxy is not rebuilding a species#

Differences between species are mostly polygenic and regulatory: thousands of small-effect variants, expression timing, developmental programs — much of it in non-coding DNA whose function is unknown. Multiplex editing can install a bounded set of named traits — coat character, cold tolerance, variants associated with body size — into a living relative, and the result is exactly that: an edited relative expressing selected derived traits, not the extinct animal. What editing cannot reach is everything not specified in sequence you possess: the epigenetic setting of embryogenesis, gut and skin microbiomes assembled horizontally, and learned behaviour. Social species transmit migration routes, calls and predator recognition culturally; an animal raised without conspecific teachers is ecologically naive even if its genome were complete — and the teachers are, by construction, extinct.

Gestation is the biological bottleneck#

The embryo needs a womb, and placentation is species-specific: implantation signalling, gestation length, foetal-maternal immunology and sheer size mismatch all reject distant surrogates. The credible routes run through close relatives — nuclear transfer into related oocytes, or stem-cell-derived embryos carried by a related host — and each costs years of reproductive physiology per species, which no amount of sequencing accelerates. Rearing then repeats the problem outside the womb.

Where the honest part lies#

What already works is genetic rescue of the living: cryobanked material from an endangered population carries alleles the survivors have lost, and cloning or assisted reproduction can put them back — a bounded, checkable intervention with no behavioural fiction attached. De-extinction as practised today sits at the proxy end of that same spectrum, and the wording matters: what returns to the reserve is an edited surrogate carrying reconstructed traits, and whether it can occupy the extinct species’ ecological role is a field experiment, not a laboratory result.