The review says: ‘Brooks asks the question: what is life? Again, scientists don’t know. There are inanimate objects. And then there living things. But no scientist on earth can tell you where the fundamental difference between thses two states lies. One definition might be that living things reproduce themselves. But then, so do some non living things, such as computer viruses.** And some living things, such as mules, do not**.’ Is that correct: mules don’t reproduce?
mules are the offspring from a cross species mating (male donkeys and female horses)
since the two diffrent species have diffrent numbers of cromosomes the offspring is infertile (most of them)
Apparently, some female mules are capable of reproduction, but no male mules are. I remember hearing about at least one instance a few years ago. It’s rare, but it can happen.
Mules have fully functional reproductive organs, but (generally) the sperm and eggs they produce are not capable uniting with each other to create a viable embryo. A female mule has ovaries which produce mature egg cells and a uterus which can sustain a pregnancy (via embryo transfer or the exceedingly rare natural pregnancy), and experiences heat cycles. A male mule has testicles which produce sperm and testosterone, and should be gelded to avoid unwanted stallion behavior. To the best of my knowledge, a male mule cannot impregnate a female mule, a female donkey, or a female horse; the few cases of pregnant female mules result from mating with a male horse or donkey.
“Living things reproduce themselves” is a poor definition at best. Many thing that are clearly alive, such as mules and domestic banana plants, can’t reproduce in the sense that they’re (functionally) infertile. The dichotomy between “inanimate objects” and “living things” seems odd as well. There’s no reason you couldn’t have a life form that doesn’t move, or even reproduce, but which is nevertheless alive in the sense that it metabolizes nutrients that it acquires from its environment.
The word mule has a connotation of sterile in and of itself. There are very rare instances of mules giving birth, but it happens less than one incident in a century. Horses and donkeys have different numbers of chromosomes, causing sterility. A boy mule is a jackass. A girl mule is a jenny.
A jackass is a male donkey (also called a jack or donkey jack). A male mule is a john mule or a jack mule. Some people use “john mule” to refer only to a male mule who has been gelded.
A jenny is a female donkey. As broomstick pointed out, a female mule is a molly or molly mule.
A male mule is often called a jack, if you happen to holding a conversation with someone intimately involved with mules. But the term ‘jackass’ means a male ass, i.e., a male animal of the donkey or burro species (Equus hemionus, IIRC). Connotatively, a jack or jenny ass usually refers to the full-size horse-sized animal, formerly a draft animal but now (IIRC) usually kept only for mule production, while burro and usually donkey refer to the pony-sized non-draft breeds within that species.
Of course, even though mules (and bananas) can’t reproduce, they’re composed of things that can and do. Mule cells can divide just like any other cell, or they wouldn’t be able to grow or heal wounds.
No. It’s the most common ‘mule’ (in the metaphorical usage) cross, hence the use of the name to describe such crosses. Interspecies crosses within a mammal genus usually but not always are infertile. (My layman’s guess is that interspecies crosses in birds among other classes tend to be fertile more commonly.) Dog-wolf and dog-coyote crosses are fairly common and fertile. (Speaking of carnivore interspecies crosses, the common name for one species derives from a mistaken belief it was a cross: Panthera leo is the lion, panthera pardus is what was in Shakespeare’s time the pard, hence the trivial name. But it was believed by 17th century biologists that the typical P. pardus was a cross between the leo and the pard, hence it was called the leopard.)
No. Many other interspecific hybrids are sterile, such the liger and tigon, crosses between lion and tiger (although as in mules females are sometimes fertile), donkey-zebra crossses, etc.
In the naked mole-rat only one female in a colony breeds, the others being functionally sterile and serving as “workers” as in ant colonies. However, this condition is temporary due to hormonal suppression by the “queen”; the workers are genetically capable of breeding if a queen is not present.
