Creationism in Crisis
Genetic Evolution of Woolly Mammoths Explained
Genetic Evolution of Woolly Mammoths Explained
Woolly mammoth, Mammuthus primigenius
Note the minuscule ears compared to modern elephants
Note the minuscule ears compared to modern elephants
Science Picture Co., Corbis
The thing about the Theory of Evolution is that, contrary to creationist claims and unlike creationism, it can make accurate predictions. Not only does that fact refute the creationist lie, but it also means that creationism has no place in science and can be dismissed as an alternative to the real science of evolution.
Because evolution is defined as change in allele frequency over time, this means that when we look for evidence of evolution in the phenotype and then map it onto changes in the genome over time, they should march in lockstep through the history of the evolving species.
And, to the great discomfort of creationists, this is exactly what scientists found when they analyzed the genomes of 22 relatively recent woolly mammoths recovered from frozen specimens that lived about 100,000 years ago, with one of the oldest known woolly mammoths, 'Chukochya', that lived about 700,000 years ago, and compared them to the genomes of modern elephants.
The work was conducted by a team led by Professor Love Dalén, professor of evolutionary genomics at the Centre for Palaeogenetics in Stockholm, Sweden and is published open access in Cell Biology. The research and its significance is explained in information made available by Cell Press and published in Science Daily:
A team of researchers compared the genomes of woolly mammoths with modern day elephants to find out what made woolly mammoths unique, both as individuals and as a species. The investigators report April 7 in the journal Current Biology that many of the woolly mammoth's trademark features -- including their woolly coats and large fat deposits -- were already genetically encoded in the earliest woolly mammoths, but these and other traits became more defined over the species' 700,000+ year existence. They also identified a gene with several mutations that may have been responsible for the woolly mammoth's miniscule ears.
To identify genes that were "highly evolved" in woolly mammoths -- meaning they had accrued a large number of mutations -- the team compared the genomes of 23 Siberian woolly mammoth with 28 modern-day Asian and African elephant genomes. Twenty-two of these woolly mammoths were relatively modern, having lived within the past 100,000 years, and sixteen of the genomes had not been previously sequenced. The twenty-third woolly mammoth genome belonged to one of the oldest known woolly mammoths, Chukochya, who lived approximately 700,000 years ago.We wanted to know what makes a mammoth a woolly mammoth. Woolly mammoths have some very characteristic morphological features, like their thick fur and small ears, that you obviously expect based on what frozen specimens look like, but there are also many other adaptations like fat metabolism and cold perception that are not so evident because they're at the molecular level.
We found that some of the genes that were previously thought to be special for woolly mammoths are actually variable between mammoths, which means they probably weren't as important
David Díez-del-Molino, first author
Centre for Palaeogenetics
Stockholm, Sweden.
Not surprisingly, many genes that were adaptive for woolly mammoths are related to living in cold environments. Some of these genes are shared by unrelated modern-day Arctic mammals. "We found some highly evolved genes related to fat metabolism and storage that are also found in other Arctic species like reindeer and polar bears, which means there's probably convergent evolution for these genes in cold-adapted mammals," says Díez-del-Molino.Having the Chukochya genome allowed us to identify a number of genes that evolved during the lifespan of the woolly mammoth as a species. This allows us to study evolution in real time, and we can say these specific mutations are unique to woolly mammoths, and they didn't exist in its ancestors.
The very earliest woolly mammoths weren't fully evolved. They possibly had larger ears, and their wool was different -- perhaps less insulating and fluffy compared to later woolly mammoths.
Apart from the field work, where we have to battle both polar bears and mosquitos, another aspect that makes this much more difficult is that you have to work in an ancient DNA laboratory, and that means that you have to dress up in this full-body suit with a hood and face mask and visor and double gloves, so doing the lab work is rather uncomfortable to put it mildly. I would like to highlight Marianne Dehasque, the second author of this paper, who did the herculean effort of performing lab work on most of these samples.
Professor Love Dalén, senior author
Professor of evolutionary genomics
Centre for Palaeogenetics
Stockholm, Sweden.
While previous studies have looked at the genomes of one or two woolly mammoths, this is the first comparison of a large number of mammoth genomes. This large sample size enabled the team to identify genes that were common among all woolly mammoths, and therefore likely adaptive, as opposed to genetic mutations that might only have been present in a single individual.
Overall, the 700,000-year-old Chukochya genome shared approximately 91.7% of the mutations that caused protein-coding changes in the more modern woolly mammoths. This means that many of the woolly mammoth's defining traits -- including thick fur, fat metabolism, and cold-perception abilities -- were probably already present when the woolly mammoth first diverged from its ancestor, the steppe mammoth.
However, these traits developed further in Chukochya's descendants.
More modern woolly mammoths also had several immune mutations in T cell antigens that were not seen in their ancestor. The authors speculate that these mutations may have conferred enhanced cell-mediated immunity in response to emerging viral pathogens.
Working with ancient mammoth DNA comes with a slew of hurdles. "Every step of the way, things are a bit more difficult, from fieldwork, to lab work, to bioinformatics," says Díez-del-Molino.
All the mammoths whose genomes were included in this study were collected in Siberia, but the researchers hope to branch out and compare North American woolly mammoths in the future. "We showed a couple of years ago that there was gene flow between woolly mammoths and the ancestors of Colombian mammoths, so that's something that we will need to account for because North American woolly mammoths might have been carrying non-woolly mammoth genes as well," says Dalén.
Figure 2 Categories of GO terms significantly enriched in woolly mammoths and Asian elephants
GO term categories based on enrichment of all genes for which either the woolly mammoth (left) or the Asian elephant (right) genomes carry one or more FdNs variants, using annotated African savannah elephant genes as a reference. All categories are based on GO terms enriched in each species with p ≤ 0.0001. See Tables S3 and S4 for the complete lists of GO terms and their classification by category.
GO term categories based on enrichment of all genes for which either the woolly mammoth (left) or the Asian elephant (right) genomes carry one or more FdNs variants, using annotated African savannah elephant genes as a reference. All categories are based on GO terms enriched in each species with p ≤ 0.0001. See Tables S3 and S4 for the complete lists of GO terms and their classification by category.
No sign there then of any theory in crisis as creationist frauds would have their prospective dupes believe. In fact, there is every sign that a prediction based on the Theory of Evolution - that changes in the genome over time would explain changes in the phenotype over time - proved to be true.HighlightsGraphical Abstract
- Genomes from 23 woolly mammoths and 28 extant elephants revealed adaptive differences
- Gene ontology suggested enrichment of mammoth genomic adaptations to cold environment
- Highly evolved genes included ones related to hair, skin, fat metabolism, and immunity
- Several key phenotypes appear to have evolved via heterochronous polygenic selection
Summary
Ancient genomes provide a tool to investigate the genetic basis of adaptations in extinct organisms. However, the identification of species-specific fixed genetic variants requires the analysis of genomes from multiple individuals. Moreover, the long-term scale of adaptive evolution coupled with the short-term nature of traditional time series data has made it difficult to assess when different adaptations evolved. Here, we analyze 23 woolly mammoth genomes, including one of the oldest known specimens at 700,000 years old, to identify fixed derived non-synonymous mutations unique to the species and to obtain estimates of when these mutations evolved. We find that at the time of its origin, the woolly mammoth had already acquired a broad spectrum of positively selected genes, including ones associated with hair and skin development, fat storage and metabolism, and immune system function. Our results also suggest that these phenotypes continued to evolve during the last 700,000 years, but through positive selection on different sets of genes. Finally, we also identify additional genes that underwent comparatively recent positive selection, including multiple genes related to skeletal morphology and body size, as well as one gene that may have contributed to the small ear size in Late Quaternary woolly mammoths.
Díez-del-Molino, David; Dehasque, Marianne; Chacón-Duque, J. Camilo; Pečnerová, Patrícia; Tikhonov, Alexei; Protopopov, Albert; Plotnikov, Valeri; Kanellidou, Foteini; Nikolskiy, Pavel; Mortensen, Peter; Danilov, Gleb K.; Vartanyan, Sergey; Gilbert, M. Thomas; Lister, Adrian M.; Heintzman, Peter D.; van der Valk, Tom; Dalén, Love
Genomics of adaptive evolution in the woolly mammoth
Current Biology (2023) DOI: 10.1016/j.cub.2023.03.084
Copyright: © 2023 The authors.
Published by Elsevier Inc. Open access
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)
It's another refutation of a central creationist lie and another validation of the Theory of Evolution.
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