In order to discover how the extant species have come about and what extinct relatives they had and who their ancestors were and how these species are related to one another, phylogenetic trees are produced which are based on the similarities and divergence among genotypes.
Usually, it is assumed that the genotype has been inherited and that similarities resulting in the placement of species into ‘one cluster’ (branch), are due to their shared ancestry and the passing on of the genes through breeding (including hybridization).
However, reproduction is not the only mechanism through which genes might become shared between species.
For example, in the book ‘The natural history of deer’ by Putnam, R. (1989) it has been stated,
‘Equally, adaptation to the requirements of the environment and life style are so precise, the pressure of being well adapted to ecological circumstance so strong, that particular characteristics of behaviour, ecology or physiology observed sometimes appear to be more characteristics of the type of environment occupied than of particular species – such that all species or populations adopting a particular life style within a particular environment must evolve the same characteristics.’ (pp. 3)
This statement illustrates that the sharing of lifestyle and environment can shape the similarities between species and populations.
Namely, species and populations of deer have descended from common ancestors (that used to rather resemble the chevrotains or the mouse deer) but the current genotypes and phenotypes are largely based on the environmental circumstances to which the species have had to adapt.
Thusly, the similarities between species inhabiting similar habitats could be so great that the species evolve similar characteristics even if they perhaps not as closely related and even if they live distantly from one another (e.g., in the west of temperate Europe and in the east of temperate Asia or in temperate Eurasia and in temperate North America) as long as the habitats that they have adapted to are also very similar.
This raises several issues.
For example, could we make erroneous genetic assumptions regarding the relatedness (or more precisely, the degree of relatedness) of two species if these species happened not to have been as closely related as it would be expected from their genotype which has not been based on recent common ancestry but which has evolved under the pressures of a similar environment?
For example, if two species shared a common ancestor in distant past but then diverged and evolved separately becoming distant to one another in certain characteristics; however, if after some major climatic event (e.g., the end of glaciation) these two species found themselves in similar habitats, could our genotyping methods be able to distinguish that they diverged very long ago and not recently and that the similarities between their genotypes are the result of the recent adaptations to their environment which they ‘share’ (not physically but through commonly experienced environmental pressures)?
The issue that I would like to raise furthers this challenge.
We do not know that much about intraspecific learning, i.e., the ability of one species learn from another species and to mimick them and to acquire similar life strategies.
Intraspecific learning could be very useful but it is also limited because species should occupy different niches in the environment in order to reduce competition.
Thus, there is a degree to which appropriating the behaviour of another species can be proven beneficial.
If the new behaviour puts the learner in peril due to conflicts with the ‘original masters of the skill’, it is not adaptive and would not persist long enough to become embedded in phenotypes/genotypes.
However, we live in a world where nature has been severely depleted.
Anciently, animals could enjoy a richer environment and the many extinctions during the geobiological history of our planet probably opened up niches for the survivors to occupy.
During such periods as well as in very rich habitats, the pressures of avoiding similar niche exploitation and competition might not have been as dire, and species might have been able to learn from one another and to practise the acquired skills or even choose them over their ‘old skill set’ to an extent that these behaviours would give rise to new genetic combinations if they provided reproductive success and enhanced survivorship.
Consequently, species might have become genetically more similar not based on common ancestry but based on common lifestyle which has arise through education.
These species could have been more or less closely related but for the behaviours to become common, it is more important to share certain physiological and cognitive attributes (which allow for the specific behaviours to be executed efficiently) than it is to be actually related.
It might happen that there have been shifts in genetic evolution of species not fueled by their closest relatives (who have discovered new opportunities or who have learned to avoid old dangers) but rather by other species whom they have learned from.
Although, in this post, I have targeted the most extreme possible consequence which is that of becoming genetically similar (perhaps to a degree that the taxa become considered related or more closely related than in reality), it is also possible that one species learned a behaviour from another species but this behaviour was exacted in a manner more adapted to their own physiology.
Namely, for example, if a Mustelid learned from a Canid (or vice versa), the Mustelid would not have turned into a Canid but its evolution following the learning incident might have triggered a divergence in its evolutionary path that separates the species/population from its former conspecifics.
I find it curious to entertain the idea that the path of evolution of a species might have been set by another species which perhaps belongs to an entirely different genetic family or order.
Such transformations would probably only become genetically significant if the learning was either widespread (more than one individual learned from the same ‘bright idea donor’ species) or if the species in which the learning occurred was long-lived enough, had social learning systems, could proliferate abundantly enough in order to actually pass on the skill to a great enough number of individuals.
Thus, species in which social learning is observed might be likelier to have undergone such adaptations.
It is also interesting to consider what types of species might be likelier to learn from what types of other species.
For example, it might be difficult for natural enemies to learn from one another.
On the other hand, e.g., scavengers could learn from apex predators (even if they were competitors) if the scavengers stalked the apex predators even during hunt or if the scavengers were able to study the carcass inferring the method of killing.
Perhaps it might be easy for species that already have somewhat similar interests (e.g., herbivory) to learn from one another if these species were nor direct competitors and could thereby ‘hang out’ near one another without the need to leave in the presence of the dominant species.
On the other hand, it is possible that species are not as invested in other species unless they have something in common (and by ‘something in common’ I also mean competitive, predatory, dominance hierarchy etc. interests) and would not observe their habits because it brings them little direct benefit (observing the habitats of one’s allies, competitors or predators brings more direct benefit).
Of course, it would be easiest for closely-related species to learn from one another.
Under such circumstances, it is possible that learning becomes confounded with interbreeding (hybridization).
On a slightly different note, already similar species might have become even more similar if, for example, they were forced or compelled to shift to very similar lifestyles.
As a result, it might be assumed that hybridization occurred with one species introgressing into another while, in truth, these two species simply had to become similar through similar behavioural adaptations to the new circumstances (e.g., a new type of predator pressure or extinction of an important food species etc.).
It might be important to study the phylogenetic history of a species not only within the context of climate and environment but also within the context of other species (related or unrelated) that occupied similar habitats and to consider whether learning could have occurred within the specific environmental conditions.
For example, the following questions might be asked:
- Was there great competition within the new niche that the species began to exploit at the time or where there ‘vacancies’ for more than one taxon to fill?
- Were there other species occupying that niche who were related (but not conspecifics) or not related (but capable of similar feats due to common physiological/cognitive traits and potential)?
- Would it be likelier for the species to take on a new evolutionary path ‘by accident’ (i.e., accidentally learning new skills) or was the species forced to evolve due to specific pressures which could or could not have prompted them to acquiring new habits perhaps from other species that the target species would have been in close contact with?
- Would it have been possible for the species at the time to pass on new skills through social learning at a rate great enough for these skills to become embedded in the ‘species conduct’ and thereby, eventually, its genome?
References
Putnam, R. The Natural History of Deer, Comstock Publishing Associates, UK, 1989, ISBN-13 : 978-0801422836, pp. 3
Notes by Ieva 