Ancient climate changes did not affect mammal diversity


The climate on Earth changes periodically – in this case we are not talking about the change of seasons, but about large cycles that last tens and hundreds of thousands of years and capture the entire planet. They occur due to the peculiarities of the Earth’s motion in orbit, in particular, due to the rotation of the Earth’s axis, due to fluctuations in the angle of inclination of the Earth’s axis to the plane of its orbit, and due to other astrophysical factors. As a result, the amount of sunlight reaching the earth’s surface changes (changes in sunlight are called Milankovitch cycles), and the climate becomes warmer and colder, ice melts, then grows, humidity rises, then increases, etc.

Should such changes affect biodiversity? It seems that they should: biodiversity is, roughly speaking, the number of species that are more or less adapted to the environment in which they happen to live. Not everyone is able to withstand climate change; accordingly, some species disappear during warming or cooling; on the other hand, the same changes help to form new species, for which new opportunities open up under new conditions. Maybe biodiversity will increase, maybe it will decrease, but one way or another, it must somehow change in the same rhythm as the climate.

However, staff University of Arizona came to the conclusion that climatic cycles have little effect on biodiversity – at least when it comes to the diversity of mammals in Africa over the past 5 million years. Climate change was assessed by researchers using fossil pollen, prehistoric algae, plant waxes, traces of which remained on the leaves of ancient plants, isotopes in different soil layers, and a whole range of other features. It is clear why they needed pollen and other plant residues: plants are a good indicator of how temperature, humidity, etc. are changing. By algae, you can understand how the sea level has changed. At the same time, it was necessary to create a method that would make it possible to bring such heterogeneous features together, which would make it possible to mold them into a single climatic picture. The researchers quite succeeded in this, moreover, they even managed to compare climate periods of different scales – 20 thousand years, 100 thousand and 400 thousand years.

Pollen and other things were collected in Africa, and the data obtained were compared with the fossil remains of ancient animals, mainly from the Bovine family (these include antelopes, bulls, rams, etc.). Naturally, here the problem of the incompleteness of the paleontological picture immediately arises: if we see that some species lived in the world three million years ago, and 2.9 million years ago it is no longer there, then maybe it really died out, or maybe we just didn’t find any younger remains. But here there is one simple method that allows us to largely overcome the problem of “paleontological incompleteness”: if we have four geological periods, and in the first, second and fourth we have bones of a particular type, but in the third we do not, then it is quite obvious that the same species lived in this period too (after all, it did not fly away in its entirety to another planet).

As a result, the researchers were able to see a series of climatic changes corresponding to the Milankovitch astrophysical cycles by plant, algal, isotope-soil and other signs. However, no change in biodiversity has been consistent with climate change. That is, species have come and gone, but with no obvious connection to these cycles. Research results published in the journal PNAS.

Of course, the results obtained relate primarily to large mammals, primarily bovids that lived in ancient times in Africa. On the other hand, we should not forget that evolution is influenced by other factors that work together with the climate and which correct the climatic effects on the populations of different animals. Perhaps this should be taken into account when analyzing the evolution of human ancestors: it is unlikely that the appearance and disappearance of new “humanoid” species was subject only to climatic changes, even when such changes were quite strong.


Source: Автономная некоммерческая организация "Редакция журнала «Наука и жизнь»" by www.nkj.ru.

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