https://phys.org/news/2024-02-neanderthals-usage-complex-adhesives-reveals.html

Neanderthals created stone tools held together
by a multi-component adhesive, a team of
scientists has discovered. Its findings, which
are the earliest evidence of a complex adhesive
in Europe, suggest these predecessors to modern
humans had a higher level of cognition and
cultural development than previously thought.

"These astonishingly well-preserved tools
showcase a technical solution broadly similar
to examples of tools made by early modern
humans in Africa, but the exact recipe reflects
a Neanderthal 'spin,' which is the production
of grips for handheld tools," says Radu Iovita,
an associate professor at New York University's
Center for the Study of Human Origins.

The research team, led by Patrick Schmidt from
the University of Tübingen's Early Prehistory
and Quaternary Ecology section and Ewa
Dutkiewicz from the Museum of Prehistory and
Early History at the National Museums in Berlin,
re-examined previous finds from Le Moustier, an
archaeological site in France that was discovered
in the early 20th century.

The stone tools from Le Moustier—used by
Neanderthals during the Middle Paleolithic
period of the Mousterian between 120,000 and
40,000 years ago—are kept in the collection of
Berlin's Museum of Prehistory and Early History
and had not previously been examined in detail.
The tools were rediscovered during an internal
review of the collection and their scientific
value was recognized.

"The items had been individually wrapped and
untouched since the 1960s," says Dutkiewicz.
"As a result, the adhering remains of organic
substances were very well preserved."

The researchers discovered traces of a mixture
of ocher and bitumen on several stone tools,
such as scrapers, flakes, and blades. Ocher is
a naturally occurring earth pigment; bitumen
is a component of asphalt and can be produced
from crude oil, but also occurs naturally in
the soil.

"We were surprised that the oche content was
more than 50%," says Schmidt. "This is because
air-dried bitumen can be used unaltered as an
adhesive, but loses its adhesive properties
when such large proportions of ocher are added."
....
"It was different when we used liquid bitumen,
which is not really suitable for gluing. If 55%
ocher is added, a malleable mass is formed,"
Schmidt says.

The mixture was just sticky enough for a stone
tool to remain stuck in it, but without adhering
to hands, making it suitable material for a handle.

In fact, a microscopic examination of the use-wear
traces on these stone tools revealed that the
adhesives on the tools from Le Moustier were used
in this way.
....

https://www.science.org/doi/10.1126/sciadv.adl0822
Ochre-based compound adhesives at the Mousterian
type-site document complex cognition and high
investment

Abstract
Ancient adhesives used in multicomponent tools
may be among our best material evidences of
cultural evolution and cognitive processes in
early humans. African Homo sapiens is known to
have made compound adhesives from naturally
sticky substances and ochre, a technical
behavior proposed to mark the advent of
elaborate cognitive processes in our species.
Foragers of the European Middle Paleolithic
also used glues, but evidence of ochre-based
compound adhesives is unknown. Here, we present
evidence of this kind. Bitumen was mixed with
high loads of goethite ochre to make compound
adhesives at the type-site of the Mousterian,
Le Moustier (France). Ochre loads were so high
that they lowered the adhesive’s performance
in classical hafting situations where stone
implements are glued to handles. However, when
used as handheld grips on cutting or scraping
tools, a behavior known from Neanderthals,
high-ochre adhesives present a real benefit,
improving their solidity and rigidity. Our
findings help understand the implications of
Pleistocene adhesive making.