During evolution, it is well established that “species come, and species go.” A species appears (because of a new ecological niche that is favorable) and, later on, a species can become extinct (the environment is no longer favorable for its survival). There are both biological and environmental “drivers” that influence the rates of species initiation and species extinction. The few studies that have quantified the relative contributions of these two drivers have concluded there exists a complex relationship. However, in the attached article, authors report an unexpectedly simple pattern of driver action in peak evolutionary success.
Between a species originating and becoming extinct, its evolutionary success can be measured in a number of ways, such as the extent of its geographical range. Such metrics often form a ‘bell-shaped’ curve [see Fig. 1 of editorial, attached], with a rise towards a central peak, followed by a decline to extinction. Why this pattern occurs so often and the degree to which biological and environmental factors influence this trajectory has long been a matter of debate. To assess the relative role of biological factors (e.g. competition between organisms), and environmental factors in evolutionary trajectories, authors analysed the fossil record of large herbivorous (plant-eating) mammals. This grouping offers several advantages for this type of analysis. For instance, the authors could solve the problem of finding consistent regional ancient environmental data, because the height of these mammals’ teeth correlates strongly with characteristics of their environment, including rain/snow precipitation levels and the amount of plant material in the ecosystem.
In the fossil record, a taxon (species, family or class of animal) exhibits a regular pattern of waxing and waning of occupancy, range or diversity between the time of their origin and their extinction. This pattern appears to contradict the law of constant extinction, which states that “the probability of extinction in a given taxon is independent of that taxon’s age.” It is nevertheless well established for species, genera and higher taxa of terrestrial
mammals, marine invertebrates, marine microorganisms, and recent Hawaiian clades of animals and plants. Authors herein demonstrate that the apparent contradiction between a stochastically constant extinction rate and the seemingly deterministic waxing and waning pattern of taxa disappears when one considers their peak of expansion rather than their final extinction. To a first approximation, authors found that biological drivers of evolution pertain mainly to the peak of taxon expansion, whereas environmental drivers mainly apply to taxon extinction.
The Red Queen hypothesis, which emphasizes biological interactions, was originally proposed as an explanation of the law of constant extinction. Since then, much effort has been devoted to determining how this hypothesis, emphasizing competition for resources, relates to the effects of environmental change. One proposed resolution is that biological and environmental processes operate at different scales. By focusing attention on taxon expansion rather than survival, authors resolve an apparent contradiction between the seemingly deterministic waxing and waning patterns over time and the randomness of extinction that the Red Queen hypothesis implies.
And –– for those few who cannot remember, I have pasted “the Red Queen Hypothesis” below.
Nature 7 Dec 2o17; 552: 92–95 [article] and pp 35–37 [News-N-Views editorial]
Red Queen Hypothesis.––The “Red Queen” hypothesis is used to describe two similar ideas, which are both based on coevolution. The original idea is that coevolution could lead to situations for which the probability of extinction is relatively constant over millions of years (Van Valen 1973). The gist of the idea is that, in tightly coevolved interactions, evolutionary change by one species (e.g., a prey or host) could lead to extinction of other species (e.g. a predator or parasite), and that the probability of such changes might be reasonably independent of species age. Van Valen named the idea “the Red Queen hypothesis,” because, under this view, species had to “run” (evolve) in order to stay in the same place (extant). (Show me the data.)
The other idea is that coevolution, particularly between hosts and parasites, could lead to sustained oscillations in genotype frequencies (Fig. 1). This idea forms the core for one of the leading hypotheses for the persistence of sexual reproduction see Bell 1982). In species where asexual reproduction is possible (as in many plants and invertebrates), coevolutionary interactions with parasites may select for sexual reproduction in hosts as a way to reduce the risk of infection in offspring. There have been many important contributors to the Red Queen hypothesis as it applies to sex. W.D. Hamilton and John Jaenike were among the earliest pioneers of the idea.
Figure 1. Red Queendynamics: results from a computer simulation for host-parasite coevolution. The blue line gives the frequency of one host genotype; the red line gives the frequency of the parasite genotype that can infect it. Note that both genotypes oscillate over time, as if they were “running” in circles. The model assumes that hosts have self-nonself recognition systems, which can detect foreign organisms. The model also assumes that hosts and parasites both reproduce sexually.
The phrase “Red Queen hypothesis” comes from Chapter 2 in Through the Looking Glass (Lewis Carroll, 1872). In Alice’s dream about the looking glass house, she first finds that things appear left-to-right, as if shown in a mirror. She then finds that chess pieces are alive. She will later encounter several of these pieces (most notably the Red Queen), after she leaves the looking glass house to see the garden.
Alice decides that it would be easier to see the garden if she first climbs the hill, to which there appears to be a very straight path. However, as she follows the path, she finds that it leads her back to the house. When she tries to speed up, she not only returns to the house, she crashes into it. Hence, forward movement takes Alice back to her starting point (Red Queen dynamics), and rapid movement causes abrupt stops (extinction).
Eventually, Alice finds herself in a patch of very vocal and opinionated flowers; the rose is especially vocal. The flowers tell Alice that someone like her (the Red Queen) often passes through, and Alice decides to seek this person, mostly as a way to escape more verbal abuse. When Alice spots the Red Queen, she begins moving toward her. But, the Red Queen quickly disappears from sight. Alice decides to follow the advice of the rose, and go the other way (“I should advise you to walk the other way”). Immediately she comes face-to-face with the Red Queen (see Lythgoe and Read 1998).
The Red Queen then leads Alice directly to the top of the hill. Along the way, the Red Queen explains that hills can become valleys, which confuses Alice. Already, in this world, straight can become curvy, and progress can be made only by going the opposite direction; now, according to the Red Queen, hills can become valleys and valleys can become hills.
At the top of the hill, the Red Queen begins to run, faster and faster. Alice runs after the Red Queen, but is further perplexed to find that neither one seems to be moving. When they stop running, they are in exactly the same place. Alice remarks on this, to which the Red Queen responds: “Now, here, you see, it takes all the running you can do to keep in the same place”. And so it may be with coevolution. Evolutionary change may be required to stay in the same place. Cessation of change may result in extinction.
Carrol, L. 1872. Through the looking glass and what Alice found there. Macmillan, London.
Bell, G. 1982. The Masterpiece of Nature: The Evolution and Genetics of Sexuality. University of California Press, Berkeley.
Lythgoe, K. A. & Read, A. F. 1998. Catching the Red Queen? The advice of the rose. Trends Ecol. Evol. 13: 473-474.
Van Valen, L. 1973. A new evolutionary law. Evol. Theory 1: 1-30.