> The ancient ancestor of the first black widow might not have been some peculiar middle ground between benign and lethal, yet the random mutation of offspring which proliferated merely happened to be highly deadly.
This is possible but not very likely in reality.
We expect evolution to be incremental, for the following reasons:
First of all, it's very unlikely that any mutation would get to "Surprise! Lethal!" venom unless the species is already geared up to produce something venom-like, and also to store venom and to protect itself from its own venom. There's a whole bunch of new functions that are needed to be venomous, and it's vanishingly unlikely that they will all suddenly appear at the same time, even at evolutionary scale.
IMO mutations normally have small positive effects and large negative effects: they are more likely to delete or - if you're lucky - alter some existing function and very unlikely to build a whole new function (compare: a small random change to your computer code).
Even if super-lethal venom was to somehow appear overnight, then in order to reach 100% prevalence it must provide such an immediate advantage that the non-lethal spiders die out and only super-lethal spiders proliferate.
But the non-lethal spiders were surviving pretty well in order to reach that point. So, there's no reason to believe the non-lethal spiders were in particular danger or that lethal venom was needed - normally, the "Surprise! Lethal!" variant line would just quietly die out (as almost all variants do) leaving the wild non-lethal type.
As I say, the random mutation explanation is possible but not really practical.
A far more plausible scenario is an "arms race" - where venomous functions develop over time, while predators and prey develop immunity over time - as the predators (honey badger) start evolving coping mechanisms, stronger venom is needed.
This is possible but not very likely in reality.
We expect evolution to be incremental, for the following reasons:
First of all, it's very unlikely that any mutation would get to "Surprise! Lethal!" venom unless the species is already geared up to produce something venom-like, and also to store venom and to protect itself from its own venom. There's a whole bunch of new functions that are needed to be venomous, and it's vanishingly unlikely that they will all suddenly appear at the same time, even at evolutionary scale.
IMO mutations normally have small positive effects and large negative effects: they are more likely to delete or - if you're lucky - alter some existing function and very unlikely to build a whole new function (compare: a small random change to your computer code).
Even if super-lethal venom was to somehow appear overnight, then in order to reach 100% prevalence it must provide such an immediate advantage that the non-lethal spiders die out and only super-lethal spiders proliferate.
But the non-lethal spiders were surviving pretty well in order to reach that point. So, there's no reason to believe the non-lethal spiders were in particular danger or that lethal venom was needed - normally, the "Surprise! Lethal!" variant line would just quietly die out (as almost all variants do) leaving the wild non-lethal type.
As I say, the random mutation explanation is possible but not really practical.
A far more plausible scenario is an "arms race" - where venomous functions develop over time, while predators and prey develop immunity over time - as the predators (honey badger) start evolving coping mechanisms, stronger venom is needed.