Tree of Life: What Creature Was at the Fork?

[rush1169]

I can show you creatures with only 80% matching DNA that have been separated for millions of years that are brought back together and breed just fine. I can also show you creatures with 99.9% identical DNA that cannot breed. These examples that I show you will confirm that there is no correlation between matching DNA and ability to breed

Please show me

Take a look at this paper:

Evolutionary animation: How do molecular phylogenies compare to Mayr's reconstruction of speciation patterns in the sea?

It's a nice summary showing how the rate of gamete evolution is decoupled from the rate of genomic evolution in sea urchins. In other words, you can have species with very similar DNA that are incompatible and others with dissimilar DNA that are compatible. Let me know if you want more.

That paper demonstrates neither. It was about divergent evolution in sea urchins that divided 250,000 to 13,000,000 years ago. Sometimes divergent sea urchins can't breed because of a changed gamete protein and sometimes they can't breed because they've been separated for a long time.

Hopefully we can return to topic.

It's a little difficult to have a conversation with one person (Loudmouth) who says there was never an individual born with human-compatible gametes and another person (CabVet) who says, "I'll play. . .yes there was an individual born with human-compatible gametes. . . .There is no such thing as a first individual of a species. Yes, at some point a single individual became compatible with us. . ."

I'd really like to discuss the arrival of the first human gamete producer. However, if neither of you think a first human gamete producer ever existed, then I suppose we just have to agree to disagree.

 

[CabVet]

That paper demonstrates neither. It was about divergent evolution in sea urchins that divided 250,000 to 13,000,000 years ago. Sometimes divergent sea urchins can't breed because of a changed gamete protein and sometimes they can't breed because they've been separated for a long time.

You didn't read the paper. You didn't even read the abstract. In sea urchins, genetic distance is not related to gamete compatibility. And that was your original question.

Hopefully we can return to topic.

It's a little difficult to have a conversation with one person (Loudmouth) who says there was never an individual born with human-compatible gametes and another person (CabVet) who says, "I'll play. . .yes there was an individual born with human-compatible gametes. . . .There is no such thing as a first individual of a species. Yes, at some point a single individual became compatible with us. . ."

We are saying the same thing. That person who was human compatible was also compatible with every member of the species living with him or her. Biology is not black and white, with very few exceptions, there is no single point in time where a species "begins". There is no answer to the question: what came first, the chicken or the egg?

I'd really like to discuss the arrival of the first human gamete producer. However, if neither of you think a first human gamete producer ever existed, then I suppose we just have to agree to disagree.

I already said such a person existed. I also said that person was also compatible with what came before. Therefore it was an intermediate. What else do you want to discuss about it?

 

[mzungu]

It's a little difficult to have a conversation with one person (Loudmouth) who says there was never an individual born with human-compatible gametes and another person (CabVet) who says, "I'll play. . .yes there was an individual born with human-compatible gametes. . . .There is no such thing as a first individual of a species. Yes, at some point a single individual became compatible with us. . ."

I'd really like to discuss the arrival of the first human gamete producer. However, if neither of you think a first human gamete producer ever existed, then I suppose we just have to agree to disagree.

That "first" individual was also compatible with the previous generations therefore he qualifies as human too. Thus your argument falls short. There is no first human as per your argument.

 

[Loudmouth]

It's a little difficult to have a conversation with one person (Loudmouth) who says there was never an individual born with human-compatible gametes . . .

You are putting words in my mouth.

1. Which individuals you label as human or non-human is a matter of semantics, so it is irrelevant to this discussion.

2. If you go back in time you will find individuals with reduced compatibility compared to modern humans. What I have said is that it would be nearly impossible to ensure 100% incompatibility through experimentation.

I'd really like to discuss the arrival of the first human gamete producer.

What you label human and non-human is entirely arbitrary. I would just leave the label off.

 

[rush1169]

So there was a first individual born that produces a gamete that could mate with a human. This individual could mate with creatures that cannot mate with humans or it could mate with humans. Either case results in a fertile, viable offspring. This individual gained human compatibility due to a mutation in it's DNA. While that mutation didn't affect it's ability to breed with it's contemporaries, that mutation does prevent humans from mating with it's contemporaries. This individual is the first intermediate between non-humans and humans.

Would this individual be consider two different species?

If that individual was found in a grave, skeleton intact, would the bones indicate it was human or would the bones indicate that it was some other? What is your best guess?

 

[Loudmouth]

So there was a first individual born that produces a gamete that could mate with a human. This individual could mate with creatures that cannot mate with humans or it could mate with humans. Either case results in a fertile, viable offspring. This individual gained human compatibility due to a mutation in it's DNA. While that mutation didn't affect it's ability to breed with it's contemporaries, that mutation does prevent humans from mating with it's contemporaries. This individual is the first intermediate between non-humans and humans.

Again, just leave the label "human" out of your description and try it again. The line you draw between human and non-human is driven by your conclusion, not the data.

Would this individual be consider two different species?

Species are populations, not individuals.

If that individual was found in a grave, skeleton intact, would the bones indicate it was human or would the bones indicate that it was some other? What is your best guess?

My guess is that you still don't understand the arbitrary nature of dividing a lineage into separate species along a time span. It is just as arbitrary as separating humans into two groups: short and tall. Where people draw the line will be to their own liking and not a real dividing line that exists in nature.

 

[mzungu]

So there was a first individual born that produces a gamete that could mate with a human. This individual could mate with creatures that cannot mate with humans or it could mate with humans. Either case results in a fertile, viable offspring. This individual gained human compatibility due to a mutation in it's DNA. While that mutation didn't affect it's ability to breed with it's contemporaries, that mutation does prevent humans from mating with it's contemporaries. This individual is the first intermediate between non-humans and humans.

Would this individual be consider two different species?

If that individual was found in a grave, skeleton intact, would the bones indicate it was human or would the bones indicate that it was some other? What is your best guess?

A creature that mates with a human and produces an offspring is a human. But wait, the same creature also mates with another creature from the previous generation and also produces an offspring but this other creature is not human because it cannot produce an offspring with a human.

Now we have a serious problem. How can the middle creature be human and yet mate with a non human creature and produce an offspring?

The only way out of this Rush is to remove the label human.

Do you see what I mean Rush?

 

[Kylie]

So there was a first individual born that produces a gamete that could mate with a human. This individual could mate with creatures that cannot mate with humans or it could mate with humans. Either case results in a fertile, viable offspring. This individual gained human compatibility due to a mutation in it's DNA. While that mutation didn't affect it's ability to breed with it's contemporaries, that mutation does prevent humans from mating with it's contemporaries. This individual is the first intermediate between non-humans and humans.

Not quite. The changes are so gradual that if one member of a population could interbreed with humans, most likely all the members of that population could.

Would this individual be consider two different species?

No. Any creature that this individual could interbreed with would be considered the same species. But species is an example of that lightswitch yes/no thinking I;ve mentioned.

If that individual was found in a grave, skeleton intact, would the bones indicate it was human or would the bones indicate that it was some other? What is your best guess?

Probably it would appear to be a creature that is very similar to modern humans but not quite the same.

 

[BaconWizard]

I think (personal theory, not proven) that an example of a creature or creatures that are at the fork might be horses vs donkeys

Or tigers vs lions.

Reason being they are still close enough to breed with each other, but their offspring cannot produce another generation except extremely rarely.

So to my thinking, these are two almost-same-but-not-quite species that say 20,000 years ago were probably the same species with just slightly different colouring, and before that, no difference at all.