Fossil evidence from the Iberian Peninsula is essential for understanding Neandertal evolution and history. Since 2000, a new sample ≈43,000 years old has been systematically recovered at the El Sidrón cave site (Asturias, Spain). Human remains almost exclusively compose the bone assemblage. All of the skeletal parts are preserved, and there is a moderate occurrence of Middle Paleolithic stone tools. A minimum number of eight individuals are represented, and ancient mtDNA has been extracted from dental and osteological remains. Paleobiology of the El Sidrón archaic humans fits the pattern found in other Neandertal samples: a high incidence of dental hypoplasia and interproximal grooves, yet no traumatic lesions are present. Moreover, unambiguous evidence of human-induced modifications has been found on the human remains. Morphologically, the El Sidrón humans show a large number of Neandertal lineage-derived features even though certain traits place the sample at the limits of Neandertal variation. Integrating the El Sidrón human mandibles into the larger Neandertal sample reveals a north–south geographic patterning, with southern Neandertals showing broader faces with increased lower facial heights. The large El Sidrón sample therefore augments the European evolutionary lineage fossil record and supports ecogeographical variability across Neandertal populations.

Host-rock, speleothems, and rock art paintings from Altamira and Tito Bustillo Caves (northern Spain) are coated by dense biofilms of phototrophic microorganisms (cyanobacteria and algae) and networks of heterotrophic bacteria (mainly actinomycetes). These microorganisms induce constructive (calcification, crystalline precipitates) and destructive fabrics (irregular etching, spiky calcite). To assess the microbial impact on both caves - which contain valuable rock art paintings - mineralogical, petrographical, hydrochemical, microenvironmental, and microbiological studies were carried out. The identified damage includes: (1) covering (scattered colored spots, whitish powdery patinas)of paintings by the microbial communities themselves and/or by their metabolic activity (including biofilms and 'bioinduced' precipitates); (2) chemical alteration, such as microbially mediated dissolution; and (3) mechanical alteration, such as substratum breakdown and scaling. In addition, some types of speleothems, such as hydromagnesite coatings, traditionally attributed to inorganic precipitation, can be considered to be a product of microbial activity, as this activity could foster the precipitation of Ca–Mg-carbonates by creating conditions of high alkalinity with low PCO 2 values. Hydrochemical, geochemical, and microenvironmental data exclude an inorganic process in the precipitation of hydromagnesite and huntite in Altamira Cave.

Despite evidence of damaging human impacts, cave paintings may again be threatened if visitors are allowed access.