New answers tagged evolution
0
Ammonites are not strictly defined. One can reffer to ammonites as to the whole group of ammonoids (Ammonoidea, ammonites sensu latto). This is common, but not supported by most researchers. Researchers use the term "ammonoid" for paleozoic ammonoidea and "ammonite" for Jurassic and Cretaceous Ammonoidea (ammonites sensu stricto). Ammonites sensu stricto ...
1
Actually, it's got nothing to do with evolution or even human biology.
Why?
What’s in a name? That which we call a rose,
By any other name would still smell as sweet. William Shakespeare.
First, try to define visible yourself. Next look at the definition of it in various respected dictionaries; in our context it means
that can be seen
Consider the ...
2
is it necessary that a given species must have at least one common ancestor?
You could imagine a species divided into groups, each group having a single common ancestor. In that case, you might ask, do the common ancestors themselves have a common ancestor, somewhere further back? Our current hypothesis is that, if you go back far enough you can find a ...
3
any giving individual alive today will be either an ancestor to ALL of the humans (in that future time) or none of them. What is the rationale behind this?
It's a simple mathematical observation nothing more than that.
One that doesn't actually require doing any math to understand.
Take a few billion people, let them mix & breed freely within the ...
1
What you could do is to take a look at diagrams such as this one:
You can make a google image search for "Cavalli Sforza" and get a lot of similar diagrams. This diagram is using a concept known as genetic distance by fixation index. This is a way to measure how different different ethnic groups are genetically. From the diagram it is easy to see that there ...
6
Welcome to Biology.SE!
Did we evolve from Africans?
Who is "we" in your sentence?
Although, it might not have been your intent, you seem to exclude Africans (and people of recent African descent) from the "we" (which would be rather insulting)!
I will rephrase your question. I will pick "caucasians" (thinking that you might be caucasians and by "we" ...
1
There is a concept known as "heritability" which essentially is a measure of how much of the variability in a certain trait that is due to genetic factors. This is closely related to regression to the mean. Now for length the heritability sometimes is estimated, by measuring the lengths of many parents and their offspring, to be around 0.7. This means that ...
1
Re a fly evolving into a rabbit, theoretically yes, practically no. Insects (and invertebrates in general) made some evolutionary "choices" like having an exoskeleton & breathing through trachea that put serious limits on their maximum size. (And vertebrates, particularly warm-blooded mammals & birds, likewise have limits on their minimum size.) ...
1
The two groups that you mention belong to two separated branches in the animal kingdom. The fly and all insects are protostomes and the rabbit and all mammals are deuterostomes. In the first, the embryonic opening (the blastopore) becomes the mouth, while in the second, it becomes the anus. Wiki
At first glance, it seems like a simple difference. But it ...
2
Insects and mammals diverged from one-another over 500 million years ago. For most of Earths 4.5 billion year history, life was single-celled, or organized into colonies of single-celled organisms. Likely sometime shortly before the Cambrian, multicellular animals evolved. The first multi-celled animals were likely a kind of colony that was not ...
3
There are several purposes for log transformations, but one of the most common that occurs in biology is when changes are relative aka multiplicative. See for example this answer from CrossValidated.
If I told you that one lizard has a tail 5 cm longer than another lizard, that doesn't actually tell you much about how different it is. If the first lizard ...
1
Plants were almost always considered a separate group from fungi and animals.
As per the latest classification both animals and plants are included in the clade Opisthokonta: animals and related unicellular organisms (holozoa) form a sister clade with holomycota (contains fungi and Cristidiscoidea).
Plants (archaeplastida), aveolates and rhizaria are now ...
0
In brittle environments we often find very large range lands(grasslands, savanna etc) that are inhabited by mixed mega herds of numerous, large, grazing herbivores. It takes pack hunters to successfully predate upon these herds. Note that all the apex predators in the more densely forested biomes of non brittle environments are solitary hunters(Tiger, Jaguar,...
0
We could try to cut the answer out:
the Population Reference Bureau estimates that about 107 billion
people have ever lived
today's population is about 7.6 billion
only 0-14 of them which are in your direct linage (parents up to grand-grand parents) are alive
world population of year 1500, when exponential growth started, is estimated to about 425 million
(...
2
The polymorphism in the gene product of the human ABO locus seems
to provide an example of what the question demands. It does not
involve a gene duplication or recovery from loss of function; rather it involves changes that cause
interactions with a different ligand, and the mutations that produce
these changes have been identified and examined at a ...
4
Generally speaking, parsimony consists in not making unnecessary ad hoc hypotheses.
In the case of phylogeny, parsimony can be used at two stages: when inferring the number of character changes for a given topology and then when choosing among topologies.
One does not expect parsimony to provide the right phylogeny in any situation. It is just the most ...
3
There are very many details to address in this question. I will try to keep it brief and keep the scope of your question in mind, which is rather narrow. I also think your friend is over-simplifying and misleading you, assuming he is honest about the explanation he gave you.
We are talking about sexual reproduction, correct? Firstly, with 3+ parents:
it's ...
8
The idea of parsimony is that when constructing phylogenetic trees a simple hypothesis (e.g., four evolutionary changes are necessary to connect two taxa) is more likely to be true than a more complex hypothesis (e.g., 15 evolutionary changes) (source: Berkeley University).
The reason is that for a certain taxon to evolve, there must be a certain number of ...
-2
Perhaps they have significantly more developed aggression circuits? Maybe the parts of the brain responsible for producing aggressive behavior are excited by hormones which are much more prevalent in donkeys?
Unless you want to dismiss the causal role of biology in animal behavior, the answer to the question "Is there something about the physiology of a ...
0
Several reasons have been proposed.
We suggest that complex cycles in helminths without penetrative infective stages evolve by two essentially different processes, depending on where in the cycle a new host is inserted. In ‘upward incorporation’, a new definitive host, typically higher up a food web and which preys on the original definitive host, is ...
2
You change one thing and you have to change everything else to compensate.
Lets look at what organs are not symmetric in tetrapods, the heart and the digestive system, everything else is symmetric. Note these are symmetric in more basal vertebrates like fish.
the heart starts symmetrical in vertebrates but that changes when animals evolve independent ...
Top 50 recent answers are included
