From Newsgroup: talk.origins

https://www.science.org/content/article/saber-toothed-cats-became-inbred-and-struggled-move-they-went-extinct

It turns out that saber toothed cats were suffering inbreeding
depression as their populations declined with the advent of this
interglacial period. Like their prey their populations declined as the
cold adapted megafauna had to deal with reduced habitat as the ice melted.

It looks like the increase in the length of the glacial periods from
40,000 years to around 100,000 years doomed the ice age megafauna.
Lifeforms can become too well adapted to their environments, and have difficulty dealing with environmental changes. It is why so many
species are in danger of extinction in our tropical rain forests. These
have been stable environments for millions of years, and species have
become very well adapted to their particular niche, and it has allowed
the greatest diversity of species to evolve in this environment. Cut
down the trees and the species are not adapted to grassland and
agricultural crops.

More ice melted during the last interglacial period than has yet melted
during this one. Genetic analysis of fossils indicate that the
megafauna populations was severely affected. There was a decline in
genetic diversity, and even though the populations of rhinos rebounded
to their normal glacial period peaks the genetic diversity remained low.
My take is that very few inbred populations survived the interglacial,
so when their populations expanded the one or two surviving populations
were not able to combine to restore genetic diversity. The thing about inbreeding is that different populations become inbred (alleles
identical by descent) for different fractions of the total genetic
variation of the species. So if you have hundreds of surviving inbred populations in small isolated alpine environments, when the population
again expands as the cold returns you get a mixing of these inbred
populations and the genetic diversity of the species gets restored. The
fewer surviving inbred populations, the less genetic diversity that has
been preserved.

Research on the mammoths indicate that they were becoming better adapted
to the cold within the last half a million years and their populations
also crashed during the last interglacial. My take is that 100,000 year periods of cold were too long of a time and allowed the animals to
better adapt to those conditions, and they were less able to cope with
the warmer interglacials. The last Wrangel island mammoths likely went extinct due to inbreeding depression and the last survivors were genetic wreaks just like these sabre toothed cats.

Ron Okimoto

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