Inbreeding: mechanisms to counter it?

(from an interested layman)I was thinking a bit about how the first steps in speciation would go, in case of geographic seperation for example. The first question that came to me was whether inbreeding would be a problem, and whether maybe there are evolutionary mechanisms against it apparent in animals.Does the isolated population have to be of minimum size to not "collapse" under degeneration?Do we recognize some sort of evolved "aversion" within related animals to mate with each other, or are they totally blind for this? What is known about how humans fare in this respect, if any social or cultural influences are eliminated. Are brothers and sisters or other close relatives (in general) somehow not attracted to each other, like they can be to not related individuals?This sounded to me like an interesting topic..

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Are brothers and sisters or other close relatives (in general) somehow not attracted to each other, like they can be to not related individuals?

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Hoo boy. The whole topic of how much human behavior is based on innate drives or instincts vs how much of it is learned is pretty controversial and fraught with peril.In my opinion, if incest avoidance were instinctive then the strong taboos that proscribe it would not be necessary.I do believe that as far as the "lower" animals go, there are some species that can recognize near kin by scent and do tend to avoid breeding with them. On the other hand, many people who own pets can tell you that incest avoidance is not a necessarily strong instinct.I think that any single pair (male/female) can potentially lead to a viable population. The main problem with inbreeding is that the genetic variability of the population is reduced, so that the population may not be able to respond to even minor environmental changes. Also, if the species (like humans) only produces a small number of offspring during the lifetime of the breeding adult, then a brother/sister pairing may result in all the offspring being homozygous for deleterious alleles, which ends the reproductive history of that line right there.

Chiroptera writes:

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On the other hand, many people who own pets can tell you that incest avoidance is not a necessarily strong instinct.

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This makes sense from an evolutionary and reproductive point of view: inbreeding may result in a population with lowered adaptability, but that is better than no population at all. The reproductive opportunities of pets are frequently artificially constrained, so it is no surprise that incest would occur in those conditions.Similarly, the bar to hydridization in avian species (e.g., finch species on the Galapagos Islands) drops considerably lower under the selective pressure of limited food resources (i.e., a bad year via drought, etc.).The primary mechanism seems to be a lower number of available mates; not surprisingly, creatures will mate with those they can, and if the only available mate is a member of a different, albeit closely related, "species"...well...love will find a way.The beauty of this is that the hybrids will increase variability, thus filling additional niches (in this example, via beak size/shape, etc.), maximizing the exploitation of limited food resources without any intention or design. Although the Russian proverb claims that "Wolves eat dogs," and, indeed, the reintroducton of wolves into the U.S. Rocky Mountains has curtailed the coyote population, the Eastern coyote has been demonstrated via DNA analysis to be a wolf-coyote hybrid; a good friend in upstate New York adores his bobcat/domestic cat hybrid, Killer (who frightens me, even though he seems to like me alright)...aren't these interesting cases for questions of species?As an inveterate observer of waterfowl, I can tell you that male mallard ducks are sluts: they will copulate with Canada geese, domestic geese, exotic ducks, ANYTHING. The bumper sticker that says, "If I don't get laid soon, somebody is gonna get hurt!" was made for mallard ducks.Am I OT yet? Has anyone else read, "If All Men Were Brothers, Would You Let One Marry Your Sister?"

So I take it that in my thought experiment, I'm overestimating the detrimental effect of inbreeding on the fitness of organisms and therefore the viability of these early populations? Mind you, this is based on small anecdotes (maybe even not true) like how the English nobility has a significantly higher incidence of lunacy than the general population. adel

adel writes:

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So I take it that in my thought experiment, I'm overestimating the detrimental effect of inbreeding on the fitness of organisms and therefore the viability of these early populations? Mind you, this is based on small anecdotes (maybe even not true) like how the English nobility has a significantly higher incidence of lunacy than the general population. adel

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It seems to me that if the inbreeding is successful, that is to say, fecund, then selective pressure will cull out the problematic individuals. Eventually, sexual chromosome shuffling, mutation, and selective pressures will promote variability.As to English nobility, they don't seem any loonier than our general U.S. population: just read the polls.