Pour la Science n ° 526 – August 2021 – When pens do math

In this issue

The spots on the jaguar’s suit, the stripes of the zebra or the clownfish, the checkered shells of certain turtles, the spirals of the shells, the tree-lined architecture of the lungs, the colorful mosaic of peacock plumage. .: The living world presents an almost infinite variety of structures remarkable for their spatial order. These patterns arouse the pleasure of the eyes, but also surprise and curiosity. How are they formed? How to explain their diversity through the living? And its constancy within the same species?

Scientists have been asking these questions for a long time. We had to wait until the twentiethi century so that they get the first elements of an answer. We can first mention D’Arcy Thompson: in his book About growth and form (1917), this Scottish biologist and mathematician emphasized the importance of the laws of physics and mechanics in understanding the forms found in living organisms and their genesis.

However, it was necessary to go beyond analogies and descriptive concepts. This only happened in the 1950s with the model proposed by the British mathematician Alan Turing. This model and its later variants provide a “self-organizing” mechanism, where stable patterns can arise spontaneously in an initially homogeneous system, from the local interactions of the system components.

Another very different theory was proposed in 1976 by Lewis Wolpert, a biologist of South African descent. According to this approach, known as “instruction”, the external signals to which the components of the system react are responsible for structuring it.

Of the self-organizing model or the instructional model, which is more relevant? As Marie Manceau, a biologist at the Collège de France, tells us, everyone has their strengths and weaknesses; but the conclusion to which the work on the plumage of birds leads, and which probably applies to many other motives of the animal world, may come as a surprise. I let you find out!

News

Maths

The undecidable trajectories of a fluid

Mathematicians have just shown that it is theoretically possible to design “computers”, or universal Turing machines, from a fluid. Consequence: Determining the long-term trajectory of a fluid particle would be an undecidable problem.

Sean Bailly

cell biology

Cell death, a guarantee of tissue integrity

In certain tissues, especially those that are rapidly renewed, the removal of dead cells protects its neighbors from a similar fate to ensure the cohesion and impermeability of the whole.

Noelle Guillon

Physics

The folding of modeled books

When you fold a book, the pages resist warping by rubbing against each other. Researchers have modeled this system.

Sean Bailly

Geosciences

Plate tectonics on Venus?

Radar images of its surface suggest the existence of recent tectonic movements.

Sean Bailly

Plant biology

Vegetable lipids, a key element in their symbiosis with fungi

450 million years ago, the first terrestrial plants already provided lipids to fungi that lived in symbiosis with them.

Isabelle Bellin

Particle physics

A revised classical experiment shows the charge of the electron to the naked eye

The famous Millikan oil drop experiment, which had been established in the early 19th century xxi century the existence of an elementary electric charge, was redesigned to be able to observe with the naked eye the consequences of the absorption of an electron by a drop.

Valentí Rakovsky

Geosciences

Zealand: The geological origins of the “eighth continent” become clearer.

This mostly submerged microcontinent, the land areas of which form New Zealand and New Caledonia, contains 1 billion-year-old rocks: they come from the Rodinia supercontinent.

William Rowe-Pirra

Climatology

At the origins of the Green Sahara, two simultaneous rain systems

An African monsoon going further north than today is not enough to explain why the Sahara was covered in vegetation only 6,000 years ago. The region would also have benefited from a second source of precipitation: the rains of a Mediterranean regime.

Valentí Rakovsky

Natural environment

More than half of the world’s rivers dry up at least once a year

Between 51 and 60 percent of the world’s waterways experience at least one day a year on average without flow, according to the first global map of permanent and intermittent streams, rivers and streams.

Valentí Rakovsky

Prehistory

The burial of Mtoto, the oldest in tropical Africa

Discovered in Kenya, the burial of a three-year-old boy buried 78,000 years ago confirms the existence of funerary practices among African sapiens populations at the time of the expansion of our species around the planet.

François Savatier

Climatology

The carbon footprint of the peat bogs becomes clearer

Carbon emissions related to the drainage of peatlands for agricultural purposes are not taken into account in climate models, due to lack of sufficient data. However, they would represent 72 billion tons of carbon since the Middle Ages.

Valentí Rakovsky

Astrophysics

Finally, the fusion of a black hole and a neutron star was observed

Possible scenarios for the coalescence of compact objects were missing a black hole and a neutron star. It was just detected … twice, ten days apart.

Sean Bailly

Physics

Physicist Jean Dalibard gold medal of the CNRS 2021

The researcher is rewarded for his pioneering work in the study of ultra-cold quantum systems.

Sean Bailly

Sponsored Content

Partner article

Radiation therapy for breast cancer: better preserving the heart

With nearly 60,000 new cases diagnosed each year in France, breast cancer is the most common type of cancer among women. In almost 70% of cases, treatment involves the use of radiation therapy. But despite technical advances in these protocols and better targeting of radiation to the tumor, the risk of long-term cardiac side effects remains. The Baccarat program, piloted by the IRSN, is studying the onset of this cardiotoxicity for the first time during the first twenty-four months after treatment.

IRSN

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