Best Answer:<span> </span><span>Before DNA, taxonomists use detailed comparative anatomy. As Louis Dollo, one of the greatest anatomists of all time, points out, evolution is irreversible.
Dollo's principle states:
"An organism is unable to return, even partially, to a previous stage already realized in the ranks of its ancestors.". According to this hypothesis a structure or organ that has been lost or discarded through the process of evolution will not reappear in exactly the same form in that line of organisms."
It means, that, no matter how closely two organisms may resemble one another, the products of convergent evolution can never resemble one another in every single detail. By examining them closely, evidence of separate ancestry will always reveal themselves. Dollo's principle has served taxonomy very well, although some taxonomists have unwisely abandoned comparative anatomy and rely instead on superficial similarity. They claim, for example, that bird hands must be the same as theropod hands because both of them have 3 fingers. Comparative anatomists, OTOH, would point out that bird hands have fingers 2-3-4 because of evidence from developmental biology and the 3 fingers of theropod hands are 1-2-3 based on fossil evidence, since primitive theropods such as Eoraptor and Herrerasaurus have vestigial fingers 4 and 5. Therefore, using Dollo's principle, we have determined that birds and theropods have evolved their 3 fingered hands independently of each other from a common ancestor with a 5 fingered hand.
Finally, to answer the question of whether snakes and worms share a recent common ancestor, we apply Dollo's principle by examining both animals in detail. Snakes have a vertebral column. They have jaws. Snakes have a lung and they have scales made of beta keratin. These structures are absent from worms. OTOH, these same structures are found only in vertebrates, but not in all vertebrates. The particular subgroup of vertebrates that have these uniquely shared characters are in fact the reptiles. Snakes therefore are reptiles, not worms. Further, since snakes and lizards share the unique character of paired hemipenes, snakes are in fact close relatives of lizards. Using Dollo's principle to study worms, we can also determine that not all worms share a recent common ancestor either. Some worms for example, have a coelom, but some have a pseudocoelom while others, such as the flat worms, have no coelom at all. Using comparative anatomy, it has been determined that annelid worms are in fact more closely related to arthropods and molluscs than they are to the round or nematode worms.
Dollo's principle has in fact resulted in a highly stable and useful classification. However, many contemporary taxonomists are either ignorant of it or disdains its use. The result is taxonomic chaos generated by those who fail to realize how powerful and useful Dollo's principle really is.</span>
Human reproduction<span> takes place as internal fertilisation by sexual intercourse. During this </span>process<span>, the male inserts his penis, which needs to be erect, into the female's vagina, and then either partner initiates rhythmic pelvic thrusts until the male ejaculates semen, which contains sperm, into the vaginal canal.</span>
Answer; Insulin and the growth hormone The hormones that are involved in building and maintaining healthy bone tissues are Insulin and growth hormone
Explanation; Insulin has some anabolic properties for bone. It is uncertain whether insulin stimulates bone directly or indirectly by increasing muscle work and thus skeletal loading. Growth hormone is a peptide hormone secreted from the pituitary gland under the control of hypothalamus. It directly and through IGF-I stimulates osteoblast proliferation and activity, promoting bone formation. Additionally it stimulates osteoclast differentiation and activity,promoting bone resorption.
Institutional review board protects the rights of human research.
They are involved with reviewing of all research that involves the use of humans before it is conducted and protect the welfare of the human involve and the privacy.
The member of the board must be 5 and above and it include people from different fields that are knowledgeable and will provide findings on human research. A non scientist is also involve and someone from other field.
Body functions stimulated by the parasympathetic nervous system (PSNS) include sexual arousal, salivation, lacrimation, urination, digestion, and defecation. The PSNS primarily uses acetylcholine as its neurotransmitter. Peptides (such as cholecystokinin) may also act on the PSNS as neurotransmitters. The parasympathetic nervous system is composed mainly of the cranial and sacral spinal nerves.
