Because Hra'vakh are genetically baseline to humans, hybridization is possible. The first hybrid born was Julianne Flaherty, who later went on to become the Earthling ambassador to Hra. Other notable hybrids include Damian Wheeler and Saia Fallwell-Sturgis.
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The differences between hra'vakh and hybrids mostly come from the human DNA, and can be grouped into developmental, physical, and psychological categories.
The gestation period for a hybrid depends on the mother: if she is a human, it is forty weeks; if she is hra'vakh, it is two Hra years, or approximately twenty-six weeks. But regardless of the mother's species, at birth the hybrid babies are virtually the same between the two. The major developmental differences between the children and their pure-blooded parents happen postpartum.
The biggest difference between the development of hra'vakh and hybrids is the growth rate itself. Native hra'vakh grow on a logarithmic curve that approaches the human growth rate on average at around age twenty-five. This means that when a hra'vakh reaches age twenty-five on Hra, he or she is as mature as a twenty-five-year-old human; yet has taken only six human years to achieve this. Hybrids, however, regardless of the mother's species, follow the human growth rate, be they born on Earth or Hra. Etahi Fallwell-Sturgis discovered this anomaly when her daughter Saia seemed to be developing too slowly. The pediatrician said she was developing perfectly for a human, however. This sparked a study into hybrids' genetics that Etahi conducted on two of her three children once they gave consent.
Another difference in development is that hybrids don't follow Piaget's theory of cognitive development to a T; they go through the stages at a rate of roughly three times what Piaget observed. By age 4, hybrids have already reached the concrete operational stage, and generally by age seven they reach the formal operational stage.
Because hra'vakh DNA is a "aggressive", hybrids are predisposed to conditions like Dur'ashakh Syndrome, and always manifest psi powers. Because humans and hra'vakh have the same number of chromosomes, the hybridization is the same regardless of whether the sperm or egg is hra'vakh. (There are negligible developmental differences between hybrids whose fathers are hra'vakh and those whose mothers are hra'vakh.)
While Dur'ashakh Syndrome is rare among full-blooded hra'vakh, genetics and the aggressiveness of DNA predispose hybrids to be greater risks for the condition. For a full-blooded hra'vakh to manifest D'aS, he or she has to be a homozygous dominant for the gene as follows:
If both parents are carriers (heterozygous)...
| D | d | |
|---|---|---|
| D | DD | Dd |
| d | Dd | dd |
...then the probability of a child suffering from D'aS is 25%. Likewise, if one parent is a carrier and the other is homozygous recessive...
| D | d | |
|---|---|---|
| d | Dd | dd |
| d | Dd | dd |
...then no children will manifest the condition, but the probability of being a carrier would be 50%.
Here's a table of all the possible permutations:
| Parent 1 | Parent 2 | Carrier probability | Sufferer probability | Clean probability |
|---|---|---|---|---|
| DD | DD | 0% | 100% | 0% |
| DD | Dd | 50% | 50% | 0% |
| DD | dd | 100% | 0% | 0% |
| Dd | Dd | 50% | 25% | 25% |
| Dd | dd | 50% | 0% | 50% |
| dd | dd | 0% | 0% | 100% |
It is estimated that 30% of societal hra'vakh are carriers, 2% are sufferers, and the other 68% are clean. Instances are much higher among water-dwelling tribal hra'vakh due to frequent inbreeding. The desert-dwelling tribals are genetically diverse enough to have similar statistics to the societals.
Because of the nature of hra'vakh DNA, the probability that a child of a carrier and a human would manifest the disease is 50% (shown by a DH):
| D | d | |
|---|---|---|
| H | DH | dH |
| H | DH | dH |
If a full-blooded sufferer were to reproduce with a human, the probability of a D'aS suffering child escalates to 100%:
| D | D | |
|---|---|---|
| H | DH | DH |
| H | DH | DH |
However, if a "clean" hra'vakh were to reproduce with a human, no children would manifest the disease: only a higher predilection for various psi powers would result. Given the estimate that 30% of hra'vakh are carriers and 2% are sufferers, it would be logical to assume that hybrids have a 17% chance of manifesting the disease, a substantial increase from figures of full-blooded hra'vakh.