Cats and People: Children of the Ice Age

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Just how far back do people and the ancestors of domestic cats go? All the way back to Plio-Pleistocene times, when the ice ages began.

The Pliocene and Pleistocene epochs

According to the geological time scale I’m using (Gradstein and others), the Pliocene epoch ran from 5.33 million years ago to 2.59 million years ago and the Pleistocene from 2.59 million years ago to roughly 12,000 years ago, when our own epoch–the Holocene–began at the end of the last big glaciation.

Numbers are relatively dry, though. What was it really like back then?

Generally speaking, Earth started out the Pliocene a little warmer and wetter than what we’re used to today, though it was by no means the sort of greenhouse world that dinosaurs had called home. Antarctica already had been sporting varying amounts of ice for 30 million years.

As the Pliocene slowly passed, things in the Northern Hemisphere dried out more, but there were still big mammals, including rhinos, in what would seem like unusual places today– Europe and North America. The first modern horses also roamed North American plains, along with camels, llamas, and other grass-eaters. Rodents were thriving throughout the north, too.

As global climate gradually cooled down and things got even drier, Australopithecus hominids like “Lucy” in Africa–Homo wasn’t around yet–had to face predators like lions, leopards, and hyenas as well as three different sabercat species.

These big predators also threatened small cats who were living off rodents, hares, and similar prey. These little kitties included one that left fossils in what is now Kenya more than 4 million years ago. This is the oldest known Felis, and it might have been a founder of the whole domestic-cat lineage.

Then, around 2.5 million years ago, the planet’s boundary conditions crossed some yet-to-be-identified threshold. Glaciers appeared in the Northern Hemisphere. The northern Pacific Ocean cooled down. After this came the great ice sheets of the Pleistocene epoch, creeping down toward the Equator, melting back toward their roots, and then cycling forward once again.

Something in this dramatic change seems to have encouraged the evolution of both human beings and the wildcat ancestor of today’s domestic cat.

How do we know that?

Obviously no one was keeping records back then. But paleontologists have clever ways of reading the past when no human writing or artwork about it exists:

  1. Fossils: With data collected by precisely measuring skeletal and dental fossils, scientists can run statistical computer programs that sort extinct species into natural groups–called “clades.” Members of each clade share a common ancestor.

    Panthera cladogram

    Clades are used to build a sort of family tree called a cladogram. This is a big-cat cladogram. The older a lineage is, the farther off to the left it branches–evidently there is no consensus on when leopards and jaguars evolved. (Source)


  2. Molecular markers: These only work in living organisms (not for sabercats, who left no descendants). Blood samples contain DNA protein sequences and certain gene segments that give a researcher clues about how modern cats evolved. One widely accepted molecular study (Johnson and others), for example, shows that the house cat lineage first showed up around 3.4 million years ago; in terms of geologic time, that’s pretty close to the 4-million-year-old Felis fossil in Kenya, mentioned above.

Each of these paleontological methods–fossil and biomarker–has its own advantages and disadvantages. Differences in dates between the two are one major reason why human origins are controversial (see this PDF for a June 2018 overview of the debate).

The details of cat evolution are unclear, too. With this group, another complication is that the skeletons of most cats, past and present, are alike. It’s often next to impossible for a researcher to say much more about a fossil cat than that it was a large or a small animal.

But the general outlines of both human and domestic cat evolution are known.

Homo sapiens

Most sources that I’ve read seem to agree that our own ancestors split away from those of the chimpanzee around 6 million years ago, just before the Pliocene epoch began. Then, at the Plio-Pleistocene cusp 2-3 million years ago, the genus Homo first appeared.

That wasn’t yet us. No one knows exactly when Homo sapiens arrived. The oldest known human fossils, in Africa, go back some 200,000 to 300,000 years, depending on which authority you believe, while biomarkers push our origin back to 1 million years before the present.

There are also multiple models of how H. sapiens emerged. In any event, modern humans came into Europe around 45,000 years ago–and they found a little wildcat there in the woods.

Felis silvestris

At some point after the 4-million-year-old Felis fossil was laid down in Kenya, some of Africa’s small cats must have migrated up into Western Europe because an ancestral wildcat, called Martelli’s cat or Felis (silvestris) lunensis, called this region home some 2 million years ago.


F lunensis

I think this is the “Felis lunensis” type specimen–the very first one identified. (Ghedoghedo, CC BY-SA 3.0)


What happened next is unclear, apart from the fact that early wildcat evolution was probably centered in Europe (there were lots of small Pleistocene cats in the New World, too, but none of them seems to have been a wildcat).

There are good reasons for this uncertainty:

  • Cat fossils are hard to come by and difficult to identify down to the species level when they are found.
  • Biomarkers aren’t a lot of help because this lineage is very young in evolutionary terms. There just hasn’t been enough time for many helpful molecular changes.

Paleontologists have only fossil evidence to study wildcat evolution. Around 50,000 years ago, according to Yamaguchi and others (see source list), the transition from F. lunensis to F. silvestris, the modern wildcat, was almost complete.

Actually, as H. sapiens entered Europe 45,000 years ago, wildcats were doing well enough to expand into Asia and Africa. By 20,000 years ago–near the height of the last ice age–these new branches had developed into the steppe cat lineage, which includes both the Asian wildcat and the African wildcat.


wildcat threefer

The Asian (bottom) and African (top left) wildcats have shorter hair, longer legs, and a much sleeker build than the OG European wildcat (top right). (Sources: Asian wildcat, by Raja Bandi, CC BY-SA 4.0; African wildcat, by Leon Emanuel, CC BY-SA 4.0; and European wildcat, by Aconcagua (talk), CC BY-SA 3.0)


One last step in the wildcat-human saga remained–domestication, and that turned out to be a two-step after African wildcats and human beings finally connected!

Today there is much concern that wildcats, particularly in Europe, are losing their genetic distinction by hybridizing with domestic cats.

It’s a complex issue, though, as we will see when we look at why the domestic cat’s scientific name is so controversial. But one facet, admittedly a minor one, that doesn’t get much coverage is this: the African wildcat’s domestic descendants are now contributing to their original ancestor’s gene pool.

Such is the natural way. But humans have a lot to say in this particular matter, and it is on us that the wildcat’s ultimate fate may depend.




Featured image: Pips van der Palloz, CC BY 2.0



Sources:

Agustí, J., and Antón, M. 2002. Mammoths, sabertooths, and hominids: 65 million years of mammalian evolution in Europe. New York and Chichester: Columbia University Press.

Belknap, D. F. 2018. Quaternary. Encylopædia Britannica. https://www.britannica.com/science/Quaternary#ref921947 Last accessed June 29, 2018.

Dennis, M. Y.; Nuttle, X.; Sudmant, P. H.; Antonacci, F.; and others. 2012. Evolution of human-specific neural SRGAP2 genes by incomplete segmental duplication. Cell, 149(4): 912-922.

Galway-Witham, J., and Stringer, C. 2018. How did Homo sapiens evolve? Science, 360(6395): 1296-1298.

Gradstein, F. M.; Ogg, J. G.; and Hilgen, F. G. 2012. On the geologic time scale. Newsletters on Stratigraphy. 45(2):171-188.

Johnson, W. E.; Eizirik, E.; Pecon-Slattery, J.; Murphy, W. J.; and others. 2006. The late Miocene radiation of modern Felidae: A genetic assessment. Science, 311(5757): 73-77.

Kurtén, B. 1965. On the evolution of the European wild cat, Felis silvestris Schreber. Acta Zoologica Fennica, 111:3-29.

Lyle, M.; Barron, J.; Bralower, T. J.; Huber, M.; and others. 2008. Pacific Ocean and Cenozoic evolution of climate. Reviews of Geophysics, 46: RG2002

O’Brien, S. J., and Johnson, W. E. 2007. The evolution of cats. Scientific American. 297 (1):68-75.

Prothero, D. R. 2006. After the Dinosaurs: The Age of Mammals. Bloomington and Indianapolis: Indiana University Press. Retrieved from https://play.google.com/store/books/details?id=Qh82IW-HHWAC

Rose, K. D. 2006. The Beginning of the Age of Mammals. Baltimore: The Johns Hopkins University Press.

Turner, A., and M. Antón. 1997. The Big Cats and Their Fossil Relatives: An Illustrated Guide to Their Evolution and Natural History. New York: Columbia University Press.

Tuttle, R. H. 2018. Human evolution. Encylopædia Britannica. https://www.britannica.com/science/human-evolution Last accessed June 29, 2018.

Werdelin, L. 1985. Small Pleistocene felines of North America. Journal of Vertebrate Paleontology. 5(3):194-210.

Werdelin, L.; Yamaguchi, N.; Johnson, W. E.; and O’Brien, S. J.. 2010. Phylogeny and evolution of cats (Felidae), in Biology and Conservation of Wild Felids, ed. Macdonald, D. W., and Loveridge, A. J., 59-82. Oxford: Oxford University Press.

Yamaguchi, N.; Driscoll, C. A.; Kitchener, A. C.; Ward, J. M.; and Macdonald, D. W. 2004. Craniological differentiation between European wildcats (Felis silvestris silvestris), African wildcats (F. s. lybica) and Asian wildcats (F. s. ornata): Implications for their evolution and conservation. Biological Journal of the Linnean Society. 83:47-63.

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