Another interesting contribution to this series. Once again weighing in as a biologist, I think the 2D vs 3D perspective is an over simplification. There are many exceptions. Birds with flight have a 3D life history, but one finds a wide range of mating systems from life-time monogamy to extreme polygyny. A more important factor is the distribution of resources essential to breeding and a male's ability to defend resources. When resources like good nest sites or food are unevenly distributed, then a dominant male may be able to defend high quality territories and attract multiple females to mate polygynously, as in red-winged blackbirds. When nesting and feeding resources are more uniformly distributed, as in tropical rainforests, then monogamy is the more likely mating system since male contributions to rearing chicks is more important. Even in monogamous species, however, both sexes can increase the genetic diversity of their offspring through sneaky extra pair copulation. And then there are lek mating systems, where males gather in communal display areas to signal, and females visit only to obtain sperm from one male and then leave to rear offspring entirely on their own. Leks can be 2D, as in frogs and grouse, or 3D as in birds of paradise and some bats. Hard to come up with dimensional contributions to leks. Add in scramble competition mating systems when large numbers of males and females congregate for a single seasonal mating event, as in gnats and wood frogs - no rules here, it's every frog or gnat for itself. The more I've learned about mating in the myriad of different animal groups over my career, the less confident I am in coming up with "rules" to teach students.
What you point out is probably important: Key resources like nesting and food sound reasonable as ways to influence the behavior of males and females. I assume however that how easy it is to hide from the partner, and how hard it is to coerce for sex, will be too important variables independent from food or nesting.
Do you think these rules don't exist, or rather that it's hard to tell based on all the factors at play? Sounds like very complex for us to tell, but I'd be surprised if they didn't exist
Interesting points. Coerced mating is uncommon among birds, with only a few examples like mallard ducks. Since most bird chicks are helpless at hatching, males can make a significant contribution to their survival by helping to feed them. The situation is very different in mammals. Newborns depend on mother's milk. Males can't help to feed the young and so are more free to seek other mates than are adult male birds. This is why long term monogamy is relatively rare in mammals but common in birds . Males in most mammalian species maximize their reproductive success by mating with as many females as possible. Coerced mating is more common among mammals, though it generally is an alternative strategy seen mostly in young and subordinate males. Older dominant males can try to attract females by signalling as in elk or some African antelopes, or they can aggressively defend a harem of females from other males as in Elephant Seals and horses. When females can hide from dominant males, they may seek matings with other males. This has been observed in Rhesus Macaques where females will sometimes sneak off into dense vegetation for a quick mating with younger males. This may benefit females by increasing the genetic diversity of their offspring. It is hard to define clear rules because for every rule there is an exception.
When I've seen this type of issue in the past, many times the complexity emerges from a set of simple rules. It's like chess of go: two games with simple rules but devilishly hard emerging complexity. The more rules, and the harder it is to gather data, the harder it will be to distill the rules. Doesn't mean they don't exist.
Why are birds so helpless when they're born? How does that change per bird? Why isn't the mallard duck like that?
You asked why newly hatched birds are helpless (referred to as altricial) as opposed to other birds like mallards whose young are able to fend for themselves soon after hatching (precocial). Mother bird has to invest a lot of protein in an egg to support enough development of the fetuses so that they can walk and feed on their own soon after birth. In seed, fruit, and nectar eating birds it may be difficult for mother to find enough protein to invest in the egg for that much development. Precocial young in birds, mammals, and other groups have the advantage of being able to flee predators soon after hatching, whereas altricial young are helpless and depend on hiding to avoid predation. This is probably why ground nesting species like ducks and ostriches have precocial young... they need to be mobile to try to escape ground predators. Ungulates also have precocial young, probably for the same reason of escaping predators. Think antelopes on the Serengetti plain in Africa, with big cats, hyenas, and hunting dogs all looking for a meal. Primates are unusual among mammals in having helpless young and perhaps this is due to a physicial limit on how big a head can fit through the mother's birth canal.
Ah Tomas, there you go being all integrative and synthetic again! You raise several interesting points. There aren't an infinite number of "rules" here, more lots of variations on several basic themes as you suggest. Biology is an emergent phenomenon building from physics and chemistry. There are some relatively straightforward principles like the relationship between volume, surface area, and energy/metabolism. But other principles, like natural selection, are not simple or easily predicted from physics. Interactions between organisms of the same and different species, and with the physical environment, add levels of complexity in a non-linear way. This isn't to say that understanding biological systems is impossible, just very challenging. As for psychology, that's outside my zone of comfort and I will leave that one alone!
Biology isn't like chess! Much messier and more variable than chess strategy. Breeding behavior in any species evolves in response to numerous factors including risk of predation of parents and vulnerable young, opportunity to find mates, distribution of food and sites for raising young, whether a species is adapted to maximize the # of young in a variable environment or the survival to adulthood of a smaller number of young in a more stable environment, and different aspects of local ecology. The complexity/variability seen in animal mating behavior is expected given the variation in these factors. I don't think there are simple rules hiding in this complexity.
At the core level, it's pretty simple: It's natural selection.
The complexity emerges from the different habitats in which natural selection happens.
These happen to be very varied—usually because of another source of emergent complexity: physics.
Physics is pretty simple. You have 4 laws (maybe just one?) that unifies nearly everything, but then these laws have an emergent complexity that creates many different types of worlds and climates.
The combination of physics plus natural selection brings and even more complex set of emergent complexity. It might be hard to see through it, the same way as we believed physics was created by gods because we didn't understand any better.
I intuit that the same is true for biology. You mention some of the variables of environments that nudge natural selection in different directions. There probably are many indeed. But just to take a few of your examples:
- Risk of predation, opportunity to find mates, and distribution of food are probably very interconnected. I'm going to guess they are all the result of a high density of heat, water, and nutrients. It's unsurprising that the highest biodiversity is found in tropical rainforests. All together, they generate more food, which generates more herbivores, and carnivores. So more opportunity to find mates but also more predators.
- Temperature is probably another variable, since colder temps will require more insulation, so a higher volume-to-surface ratio, so bigger, fatter animals
- There are different strategies that might work in the same environment. For example, optimizing for quantity of offspring vs quality. Humans famously optimize for quality, but fruit flies optimize for quantity, and they're pretty good at it. So this might be a rule that creates a spectrum of species rather than nudging them in one direction or the other.
- Similarly, there's probably another gradient of aggregation. You can be disaggregated but successful (eg bacteria, viruses), or very highly aggregated (multi-cellular bodies, social species), or anything in between, and many of these variations might fit the environment.
So I think we agree that there's many such rules. What I'm arguing is that there's a *finite number* of these rules, and that it's probably closer to 10 than it is to 100, to explain the vast majority of natural selection.
Another comparison might be what's happening with psychology right now, where hundreds of cognitive biases are being summarized into a few core biases.
Fascinating concept here "Since males can’t control the female, and the female cheats, males need to find ways to increase the probability that they are the fathers" which likely explains the prevalence of sexual violence committed by groups of left behind men in communities where the women are doing economically better or have potential mate choices from a higher social class.
I've seen areas with poor socio economic prospects, especially those that were once better off, tend to have much higher rates of sexual violence against women. It tends to be done in groups, by low status men. Inevitably against women who appear to be heading off to higher status or better prospects.
Hmm group violence on women doesn't increase the confidence on paternity. It does increase the likelihood of siring offspring.
This sounds like it falls in the standard case of "in the absence of other institutions that hinder their behavior, men will coerce women into sex". Especially true for men who will have a hard time aspiring to a long-term mate—ie low status. So what you say is true, but maybe not due to confidence on paternity
Another interesting contribution to this series. Once again weighing in as a biologist, I think the 2D vs 3D perspective is an over simplification. There are many exceptions. Birds with flight have a 3D life history, but one finds a wide range of mating systems from life-time monogamy to extreme polygyny. A more important factor is the distribution of resources essential to breeding and a male's ability to defend resources. When resources like good nest sites or food are unevenly distributed, then a dominant male may be able to defend high quality territories and attract multiple females to mate polygynously, as in red-winged blackbirds. When nesting and feeding resources are more uniformly distributed, as in tropical rainforests, then monogamy is the more likely mating system since male contributions to rearing chicks is more important. Even in monogamous species, however, both sexes can increase the genetic diversity of their offspring through sneaky extra pair copulation. And then there are lek mating systems, where males gather in communal display areas to signal, and females visit only to obtain sperm from one male and then leave to rear offspring entirely on their own. Leks can be 2D, as in frogs and grouse, or 3D as in birds of paradise and some bats. Hard to come up with dimensional contributions to leks. Add in scramble competition mating systems when large numbers of males and females congregate for a single seasonal mating event, as in gnats and wood frogs - no rules here, it's every frog or gnat for itself. The more I've learned about mating in the myriad of different animal groups over my career, the less confident I am in coming up with "rules" to teach students.
Thank you!
What you point out is probably important: Key resources like nesting and food sound reasonable as ways to influence the behavior of males and females. I assume however that how easy it is to hide from the partner, and how hard it is to coerce for sex, will be too important variables independent from food or nesting.
Do you think these rules don't exist, or rather that it's hard to tell based on all the factors at play? Sounds like very complex for us to tell, but I'd be surprised if they didn't exist
Interesting points. Coerced mating is uncommon among birds, with only a few examples like mallard ducks. Since most bird chicks are helpless at hatching, males can make a significant contribution to their survival by helping to feed them. The situation is very different in mammals. Newborns depend on mother's milk. Males can't help to feed the young and so are more free to seek other mates than are adult male birds. This is why long term monogamy is relatively rare in mammals but common in birds . Males in most mammalian species maximize their reproductive success by mating with as many females as possible. Coerced mating is more common among mammals, though it generally is an alternative strategy seen mostly in young and subordinate males. Older dominant males can try to attract females by signalling as in elk or some African antelopes, or they can aggressively defend a harem of females from other males as in Elephant Seals and horses. When females can hide from dominant males, they may seek matings with other males. This has been observed in Rhesus Macaques where females will sometimes sneak off into dense vegetation for a quick mating with younger males. This may benefit females by increasing the genetic diversity of their offspring. It is hard to define clear rules because for every rule there is an exception.
When I've seen this type of issue in the past, many times the complexity emerges from a set of simple rules. It's like chess of go: two games with simple rules but devilishly hard emerging complexity. The more rules, and the harder it is to gather data, the harder it will be to distill the rules. Doesn't mean they don't exist.
Why are birds so helpless when they're born? How does that change per bird? Why isn't the mallard duck like that?
You asked why newly hatched birds are helpless (referred to as altricial) as opposed to other birds like mallards whose young are able to fend for themselves soon after hatching (precocial). Mother bird has to invest a lot of protein in an egg to support enough development of the fetuses so that they can walk and feed on their own soon after birth. In seed, fruit, and nectar eating birds it may be difficult for mother to find enough protein to invest in the egg for that much development. Precocial young in birds, mammals, and other groups have the advantage of being able to flee predators soon after hatching, whereas altricial young are helpless and depend on hiding to avoid predation. This is probably why ground nesting species like ducks and ostriches have precocial young... they need to be mobile to try to escape ground predators. Ungulates also have precocial young, probably for the same reason of escaping predators. Think antelopes on the Serengetti plain in Africa, with big cats, hyenas, and hunting dogs all looking for a meal. Primates are unusual among mammals in having helpless young and perhaps this is due to a physicial limit on how big a head can fit through the mother's birth canal.
Love this. Thanks!
You're welcome
great article, Tomas! Thanks!
A little off topic but check it out.
https://twitter.com/_borriss_/status/1707412406048063788?s=46&t=61KYCU9tDNp8gxhQcUiO4w
I’m following oh so closely
Me too. Racing to keep up!
Fascinante y especial forma de explicar las relaciones animales
Ah Tomas, there you go being all integrative and synthetic again! You raise several interesting points. There aren't an infinite number of "rules" here, more lots of variations on several basic themes as you suggest. Biology is an emergent phenomenon building from physics and chemistry. There are some relatively straightforward principles like the relationship between volume, surface area, and energy/metabolism. But other principles, like natural selection, are not simple or easily predicted from physics. Interactions between organisms of the same and different species, and with the physical environment, add levels of complexity in a non-linear way. This isn't to say that understanding biological systems is impossible, just very challenging. As for psychology, that's outside my zone of comfort and I will leave that one alone!
Biology isn't like chess! Much messier and more variable than chess strategy. Breeding behavior in any species evolves in response to numerous factors including risk of predation of parents and vulnerable young, opportunity to find mates, distribution of food and sites for raising young, whether a species is adapted to maximize the # of young in a variable environment or the survival to adulthood of a smaller number of young in a more stable environment, and different aspects of local ecology. The complexity/variability seen in animal mating behavior is expected given the variation in these factors. I don't think there are simple rules hiding in this complexity.
At the core level, it's pretty simple: It's natural selection.
The complexity emerges from the different habitats in which natural selection happens.
These happen to be very varied—usually because of another source of emergent complexity: physics.
Physics is pretty simple. You have 4 laws (maybe just one?) that unifies nearly everything, but then these laws have an emergent complexity that creates many different types of worlds and climates.
The combination of physics plus natural selection brings and even more complex set of emergent complexity. It might be hard to see through it, the same way as we believed physics was created by gods because we didn't understand any better.
I intuit that the same is true for biology. You mention some of the variables of environments that nudge natural selection in different directions. There probably are many indeed. But just to take a few of your examples:
- Risk of predation, opportunity to find mates, and distribution of food are probably very interconnected. I'm going to guess they are all the result of a high density of heat, water, and nutrients. It's unsurprising that the highest biodiversity is found in tropical rainforests. All together, they generate more food, which generates more herbivores, and carnivores. So more opportunity to find mates but also more predators.
- Temperature is probably another variable, since colder temps will require more insulation, so a higher volume-to-surface ratio, so bigger, fatter animals
- There are different strategies that might work in the same environment. For example, optimizing for quantity of offspring vs quality. Humans famously optimize for quality, but fruit flies optimize for quantity, and they're pretty good at it. So this might be a rule that creates a spectrum of species rather than nudging them in one direction or the other.
- Similarly, there's probably another gradient of aggregation. You can be disaggregated but successful (eg bacteria, viruses), or very highly aggregated (multi-cellular bodies, social species), or anything in between, and many of these variations might fit the environment.
So I think we agree that there's many such rules. What I'm arguing is that there's a *finite number* of these rules, and that it's probably closer to 10 than it is to 100, to explain the vast majority of natural selection.
Another comparison might be what's happening with psychology right now, where hundreds of cognitive biases are being summarized into a few core biases.
Fascinating concept here "Since males can’t control the female, and the female cheats, males need to find ways to increase the probability that they are the fathers" which likely explains the prevalence of sexual violence committed by groups of left behind men in communities where the women are doing economically better or have potential mate choices from a higher social class.
Not sure I follow
I've seen areas with poor socio economic prospects, especially those that were once better off, tend to have much higher rates of sexual violence against women. It tends to be done in groups, by low status men. Inevitably against women who appear to be heading off to higher status or better prospects.
Hmm group violence on women doesn't increase the confidence on paternity. It does increase the likelihood of siring offspring.
This sounds like it falls in the standard case of "in the absence of other institutions that hinder their behavior, men will coerce women into sex". Especially true for men who will have a hard time aspiring to a long-term mate—ie low status. So what you say is true, but maybe not due to confidence on paternity