5 ms·

The notion of frameshift mutations is interesting. Though, for the example he gives, I don't see why the initial mutation (large jaw, small jaw muscles) succee

by endtime 18y ago

The notion of frameshift mutations is interesting. Though, for the example he gives, I don't see why the initial mutation (large jaw, small jaw muscles) succeeded. Why wouldn't the primates with big, weak jaws be outbred before they could evolve smaller jaws and larger brains? Ah, maybe there was no real benefit to having a stronger jaw? Only solution I can think of.

deleted 18y ago
[deleted]
wolfish 18y ago
I think people often think of natural selection as only allowing the best to exist, when really it allows what can exist to exist, even if the mutation provides no benefit.
- Scriptor 18y ago
  When you get down to it, natural selection is merely about who is able to create the most successful offspring. The fact that the offspring have very similar traits as their parents is the reason why these offspring are themselves likely to reproduce successfully. The question then is weaker jaw muscles somehow became more prevalent than stronger ones. As I explained in another comment, this might be because the trait was able to survive recessively until a good genetic environment was available.
  - wolfish 18y ago
    I don't think its necessary to create the most successful offspring, merely offspring that can reproduce before they die.
- endtime 18y ago
  Well, doesn't it depend on how harsh the environment is? For example, if there's not enough food for the population then only those most capable of acquiring food will survive. But today, where we have great plenty (in some parts of the world) and advanced medical care etc, what you said is certainly true.
Scriptor 18y ago
I had the same question. It is possible that the trait survived as a recessive one for a long time. In the same way that sickle-cell is only lethal if a person has the defect in both sets of chromosomes (homozygous recessive), the weaker jaw muscles would only be a disadvantage for big-jawed primates if they were homozygous recessive. Later, when alleles for smaller jaws appeared, the weak-jaw-muscle allele had a higher chance of being propagated. Another possibility is that the myosin heavy chain, or a related regulatory function, induces larger jaws. Without this the jaw was not given enough stimulus to grow large enough.
tokenadult 18y ago
To answer your question, a lot of paleontologists believe that hominid dietary changes from cooking, which came before Homo sapiens and somewhat after the genetic change mentioned in the submitted article, eliminated selection pressure in favor of strong chewing power, because food became softer, more digestible, and thus more nourishing. This allowed the ancestral line to Homo sapiens to devote more total bodily energy to growing a large brain (also enabled by the mechanisms mentioned in the submitted article) and much less energy to developing a hindgut that can digest raw vegetable foods. So there were several synergistic influences that allowed a diverging body plan between the chimpanzee line and the Homo sapiens line. This Economist article (previously submitted to HN) http://www.economist.com/science/displaystory.cfm?story_id=13139619 http://www.economist.com/science/displaystory.cfm?story_id=1... tells part of the story. HN discussion here: http://news.ycombinator.com/item?id=490292 http://news.ycombinator.com/item?id=490292
biohacker42 18y ago
I am not an evolutionary biologist (I do write software for a lot of research biologists) but I don't think there was anyone walking around with tiny jaw muscles and a huge jaw. I suspect the development of the jaw is related to the same gene. What that article attempts to say, and fails to do it, is that HUGE changes often happen in a single generation. There's a contagious non lethal dog tumor that used to be a dog, as in an individual dog.

by endtime 18y ago

deleted 18y ago

[deleted]

wolfish 18y ago

I think people often think of natural selection as only allowing the best to exist, when really it allows what can exist to exist, even if the mutation provides no benefit.

Scriptor 18y ago
When you get down to it, natural selection is merely about who is able to create the most successful offspring. The fact that the offspring have very similar traits as their parents is the reason why these offspring are themselves likely to reproduce successfully. The question then is weaker jaw muscles somehow became more prevalent than stronger ones. As I explained in another comment, this might be because the trait was able to survive recessively until a good genetic environment was available.
- wolfish 18y ago
  I don't think its necessary to create the most successful offspring, merely offspring that can reproduce before they die.
endtime 18y ago
Well, doesn't it depend on how harsh the environment is? For example, if there's not enough food for the population then only those most capable of acquiring food will survive. But today, where we have great plenty (in some parts of the world) and advanced medical care etc, what you said is certainly true.

Scriptor 18y ago

I had the same question. It is possible that the trait survived as a recessive one for a long time. In the same way that sickle-cell is only lethal if a person has the defect in both sets of chromosomes (homozygous recessive), the weaker jaw muscles would only be a disadvantage for big-jawed primates if they were homozygous recessive. Later, when alleles for smaller jaws appeared, the weak-jaw-muscle allele had a higher chance of being propagated. Another possibility is that the myosin heavy chain, or a related regulatory function, induces larger jaws. Without this the jaw was not given enough stimulus to grow large enough.

tokenadult 18y ago

To answer your question, a lot of paleontologists believe that hominid dietary changes from cooking, which came before Homo sapiens and somewhat after the genetic change mentioned in the submitted article, eliminated selection pressure in favor of strong chewing power, because food became softer, more digestible, and thus more nourishing. This allowed the ancestral line to Homo sapiens to devote more total bodily energy to growing a large brain (also enabled by the mechanisms mentioned in the submitted article) and much less energy to developing a hindgut that can digest raw vegetable foods. So there were several synergistic influences that allowed a diverging body plan between the chimpanzee line and the Homo sapiens line. This Economist article (previously submitted to HN) http://www.economist.com/science/displaystory.cfm?story_id=13139619 http://www.economist.com/science/displaystory.cfm?story_id=1... tells part of the story. HN discussion here: http://news.ycombinator.com/item?id=490292 http://news.ycombinator.com/item?id=490292

biohacker42 18y ago

I am not an evolutionary biologist (I do write software for a lot of research biologists) but I don't think there was anyone walking around with tiny jaw muscles and a huge jaw. I suspect the development of the jaw is related to the same gene. What that article attempts to say, and fails to do it, is that HUGE changes often happen in a single generation. There's a contagious non lethal dog tumor that used to be a dog, as in an individual dog.