WHY does the topic of “evolution” keep “popping up” — in these Gene-Environment Interactions email blogs?? The answer, of course, is that the organism’s genome evolves because of the constantly-changing environment to which the organism is exposed. Consequently, every evolutionary event is connected, one way or another, to gene-environment interactions.
There are two fundamental types of evolution, which describe how species adapt to their environments over time: divergent (the more popular one that everyone knows) and convergent. Divergent evolution occurs when closely related species evolve different traits, as they adapt to varying ecological niches, often resulting in a wide variety of forms and behaviors. A classic example is Darwin’s finches, which evolved from a single ancestor to exploit different food sources on the Galápagos Islands, leading to diverse beak shapes and sizes suited to their unique diets. Divergent evolution is thus most likely caused by de novo mutations, gene-duplication events, and crossing-over and slippage during cDNA transcription into mRNA…
Convergent evolution, in contrast, refers to the process in which unrelated species develop similar traits or adaptations due to facing similar environmental pressures (e.g., sharks, dolphins, and ichthyosaurs all evolved streamlined bodies and other adaptations for life in the ocean — despite their differing evolutionary backgrounds).
Another great example of convergent evolution is one I’ve often used in lectures on “evolution” to high school students: The Antarctic notothenioid (Dissostichus mawsoni) antifreeze glycoprotein gene (AFGP) arose from a pancreas-derived (trypsinogen) gene and evolved into a segment with 41 repeats (9 nucleotides encoding Thr-Ala-Ala). The origin of this AFGP gene correlates well with the estimated time (~10-14 million years ago; MYA) when the Antarctic Ocean froze over — because if fish had a strong desire to survive water temperatures at or below zero Centigrade, they needed “antifreeze” A.S.A.P. 😊
Interestingly, the AFGP gene was found in Arctic cod (Boreogadus saida) by scientists using the Antarctic AFGP repeat “Thr-Ala-Ala” as the probe. This Arctic AFGP protein was discovered to be derived from a totally different gene (located far away in the genome from the location of the Antarctic AFGP gene) — originating ~2.5 MYA — which coincides with the occurrence of Arctic Ocean glaciation. Here we have different fish species, located at the two ends of the Earth, needing a protein (at different geo-evolutionary times) in response to a drastic change in their environment (i.e., extreme life-threatening danger of cold temperatures)…!!
Both divergent, and convergent, evolutionary processes therefore illustrate the dynamic interplay between organisms and their environments — emphasizing that adaptation can arise through both shared ancestry and independent evolutionary pathways. Understanding these concepts provides insight into the complexity of life on Earth and the mechanisms driving biodiversity. [Thus, this story is politically acceptably “woke,” because it describes “diversity, equity and inclusivity”.]
During evolution of life on Earth, the colonization of land by life is one of the most notable transitions in the history of Earth — substantially shaping modern ecosystems, life forms, and the planet itself. Terrestrialization has occurred multiple times, independently, within the animal kingdom — including among arthropods, vertebrates, rotifers, mollusks, annelids, nematodes, tardigrades, and onychophorans. Nonetheless, each of these natural events in terrestrialization had to overcome similar physiological and environmental challenges. Phenotypic adaptations — e.g., water-retentive skin or cuticle, adapted immune systems, changes in skeletal design and locomotion, elevated metabolic rates, developmental adaptations (such as encapsulated larvae and brooding), and adaptation of vision in a non-aquatic environment. All these adaptations show widespread convergent evolution across terrestrial lineages; this suggests largely predictable responses to similar environmental pressures.
At the genotype level, recent studies have shown that genomic changes (including gene innovation, duplication, and loss) were crucial to major metazoan evolutionary transitions. Furthermore, specific genes (e.g., aquaporin-coding genes) have been linked to terrestrialization in several clades, and genomic changes have been associated with individual lineages; these support the roles of genes related to metabolism, stress response, osmoregulation, and immunity in terrestrialization. However, in comparison to land plants, the genomic basis of terrestrialization across animal lineages remains largely uncharacterized. These parallel natural experiments provide a unique opportunity to determine whether terrestrialization has led to lineage-specific contingent genomic adaptations, or whether these are predictable changes in response to the same environmental challenges.
Authors [see attached file] apply a comparative genomics pipeline to a dataset of 154 genomes (from 21 animal phyla and their outgroups) to explore the role of convergence and contingency in the evolutionary response of animal genomes to the process of terrestrialization, and to establish the timeline of acclimatization of animals to land. Their results reveal that independent terrestrial events were driven by the emergence of similar biological functions, although semi-terrestrial and fully terrestrial lineages exhibit different patterns of genomic adaptation to terrestrialization. The authors identified three temporal windows during which animals colonized land — offering a new chronological framework for these transitions.
Authors [see attached file] reconstructed the protein-coding content of the ancestral genomes linked to eleven animal terrestrialization events — to produce a timescale of terrestrialization. They uncovered distinct patterns
of gene gain and loss underlying each transition to land, but similar biological functions emerged recurrently — pointing to specific adaptations as key to life on land. We show that semi-terrestrial species evolved convergent functional patterns, in contrast with fully terrestrial lineages that followed different paths to land. The authors’ timeline supports three temporal windows of land colonization by animals during the last 487 million years, each associated with specific ecological contexts. Although each lineage exhibits distinct adaptations, there is strong evidence of convergent genome evolution across the animal kingdom — suggesting that, in large part, adaptation to life on land is predictable, linking genes to ecosystems (gene-environment interactions). 😊😉
DwN
Nature 2025; Nov 12. doi: 10.1038/s41586-025-09722-4